Exploring the Boundaries of Porphyrin Materials Synthesis ... · Exploring the Boundaries of Porphyrin Materials Synthesis by Ionic Self-Assembly i i i Acknowledgments Many people

Exploring the

Boundaries of

Porphyrin Materials

Synthesis by Ionic

Self-Assembly

João Pedro Gomes dos Santos

Mestrado em Bioquímica

Química e Bioquímica

2015

Orientador

Craig Medforth, Principal Investigator, UCIBIO@REQUIMTE

Departamento de Química e Bioquímica

Faculdade de Ciências, Universidade do Porto

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FCUP Exploring the Boundaries of Porphyrin Materials Synthesis by Ionic Self-Assembly

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Acknowledgments

Many people contributed to the success of my Master’s degree and this section is

dedicated to them.

To my family for all the support and teachings in all these years

To my girlfriend and friends for making this journey much easier and pleasant.

To Craig for accepting me into this project and for his help and teaching throughout.

To Pedro and Miguel for their help in the lab.

To Filipa and Beatriz for letting me be a teacher for the first time.

iv FCUP Exploring the Boundaries of Porphyrin Materials Synthesis by Ionic Self-Assembly


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Resumo

As porfirinas são componentes atrativos para serem usados em fotónica, catálise,

células solares e fotossíntese artificial devido as suas características catalíticas,

eletrónicas e óticas. Como resultado a síntese e possíveis aplicações de nanomateriais

de porfirinas emergiram como uma área de interesse científico nos últimos anos. Vários

métodos, tais como reprecipitação e polimerização de coordenação têm sido usados

para produzir nanomateriais constituídos por um único tipo de porfirina e a auto

montagem iónica (Ionic Self-assembly, ISA) de porfirinas com cargas opostas tem sido

usado para preparar nanomateriais catalíticos de dois tipos de porfirinas diferentes.

Neste trabalho é explorada em solução aquosa e a pH 2 a auto montagem iónica de

uma nova grande porfirina octocatiónica (LOCP) com a tetra(4-sulfonatofenil)-porfirina

(TPPS).

As reações entre as formas metálicas da TPPS (MTPPS) e a LOCP produzem materiais

que são consistentes com ISA apesar de mostrarem características estranhas não

anteriormente notadas para ISA de porfirinas.

As imagens de microscopia de transmissão eletrónica (TEM) e microscopia eletrónica

de varrimento mostram nanopartículas e placas com micrómetros de tamanho.

As reações entre a H4TPPS e a LOCP também produzem precipitados com

nanopartículas e “bolachas” com mícrones de tamanho, apesar de as reações não

demonstrarem um comportamento de ISA.

As reações entre a LOCP e dois tipos diferentes de MTPPS são também produzidas,

numa tentativa bem-sucedida de formar nanomateriais ternários de porfirina usando a

alta carga da LOCP

Palavras-chave: Porfirina, ISA, nanopartícula, LOCP, TPPS

vi FCUP Exploring the Boundaries of Porphyrin Materials Synthesis by Ionic Self-Assembly


vii

Abstract

Porphyrins are attractive components to be used in photonics, catalysis, solar cells and

artificial photosynthesis due to their catalytic, electronic and optical properties. As a result

the synthesis and possible applications of porphyrins nanomaterials have emerged as

an area of research interest in recent years. Various methods, such as reprecipitation

and coordination polymerization have been used to produce nanomaterials containing a

single porphyrin type and Ionic Self Assembly (ISA) of oppositely charged porphyrins

has been used to prepare catalytic binary porphyrin nanomaterials.

In this Master thesis, the ISA reactions of a novel Large Octacationic Porphyrin (LOCP)

with tetra (4-sulfonatophenyl)-porphyrin (TPPS) are explored in aqueous solutions at pH

2.

Reactions between Metal TPPS (MTPPS) and LOCP produce materials that are

consistent with ISA but display some unusual features not previously noted for porphyrin

ISA. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM)

images show nanoparticles and micro-sized wafers.

Reactions between H4TPPS and LOCP also produce precipitates with nanoparticles and

micro-sized wafers, although the reactions do not display ISA behaviour.

Reactions between LOCP and two different MTPPS are also performed in a successful

attempt to form ternary porphyrin nanomaterials using the high charge of LOCP.

Key words: Porphyrin, ISA, nanoparticle, LOCP, TPPS

viii FCUP Exploring the Boundaries of Porphyrin Materials Synthesis by Ionic Self-Assembly

Table of Contents

Acknowledgments ............................................................................................................ iii

Resumo..............................................................................................................................v

Abstract ............................................................................................................................ vii

Table List .......................................................................................................................... ix

Figure List ..........................................................................................................................x

List of abbreviations ........................................................................................................ xiii

1. Introduction ................................................................................................................ 1

1.1. Porphyrins .......................................................................................................... 1

1.2. Porphyrin Nanostructures .................................................................................. 2

1.3. Goals of this work .............................................................................................. 4

2. Materials and Methods .............................................................................................. 6

2.1. Porphyrins .......................................................................................................... 6

2.2. Solvents ............................................................................................................. 6

2.3. Stock solution preparation ................................................................................. 6

2.4. Sample preparation............................................................................................ 7

2.5. Ultraviolet/Visible Spectrophotometry (UV/Vis) ................................................. 7

2.6. Inductively-coupled plasma mass spectrometry (ICP-MS) ............................... 7

2.7. Transmission Electron Microscopy (TEM)......................................................... 8

2.8. Scanning Electron Microscopy (SEM) ............................................................... 8

3. Ionic Self-assembly (ISA) of Large Octacationic Porphyrin (LOCP) ...................... 10

3.1. ISA of LOCP with MTPPS ............................................................................... 10

3.2. ISA of LOCP with H4TPPS .............................................................................. 17

3.3. ISA of LOCP with two different MTPPS .......................................................... 23

4. Conclusions ............................................................................................................. 31

5. References .............................................................................................................. 33


ix

Table List

Table 1 – Substituents and important properties of in all porphyrins used in this work. . 9

Table 2 – MicroMolar concentrations and ratios used in the reactions. ........................ 10

Table 3 – Ratios determined by ICP-MS for the precipitates of reactions involving LOCP

and various MTPPS for ratios 1 to 4. ............................................................................. 11

Table 4 – Main peaks seen in UV-Vis spectra of reactant, and precipitates from reactions

of LOCP-TPPS. .............................................................................................................. 12

Table 5 – Ratios and Micro Molar concentration of Porphyrin used in the reactant

solutions and determined for the precipitates of LOCP and H4TPPS for low

H4TPPS/LOCP ratios ...................................................................................................... 17

Table 6 – Ratios and Micro Molar concentration of Porphyrin used in the reactant

solutions and determined for the precipitates of LOCP and H4TPPS for high

H4TPPS:LOCP ratios ...................................................................................................... 17

Table 7– Main peaks seen in UV-Vis spectra of stock solutions and in the

precipitates/nanostructures of various reactions. .......................................................... 17

Table 8 – Ratios in the precipitates from reactions of LOCP and various combinations of

MTPPS. The porphyrin ratios were 1:1:1 (40µM each porphyrin) ................................. 23

Table 9 – Main peaks seen in UV-Vis spectra of stock solutions and in the precipitates

of reactions of LOCP with M1TPPS and M2TPPS. ......................................................... 24

x FCUP Exploring the Boundaries of Porphyrin Materials Synthesis by Ionic Self-Assembly

Figure List

Figure 1 – Structural formula of Porphine ........................................................................ 1

Figure 2 – From left to right structural formulas of Porphine, Porphodimethane,

Porphyrinogen, ChIorin, Bacteriochlorin, lsobacteriochlorin ............................................ 1

Figure 3 – Crystal structure of LOCP. Adapted from Jiang, L. et al. ............................... 4

Figure 4 – Structural formula of LOCP ............................................................................. 4

Figure 5 – Structural formula of H4TPPS ......................................................................... 5

Figure 6 – From left to right, representations of: Side and top view of a monomer of

H4TPPS2-, side and top view of a J-aggregate................................................................. 5

Figure 7 – Structural formula of the Porphyrin that serves as a base for the porphyrins in

this work ............................................................................................................................ 6

Figure 8 – Unprotonated (left) and protonated (right) form of LOCP ............................ 10

Figure 9 – UV-Vis spectra obtained in the reaction of LOCP with SnIVTPPS in a ratio of

1:1 and 2:1 and the SnIVTPPS porphyrin. ...................................................................... 13

Figure 10 – UV-Vis spectra of the nanostructure obtained for the reaction of LOCP with

CuIITPPS in a ratio of 2:1 and the two starting porphyrins. ........................................... 13


NiIITPPS in a ratio of 2:1 and the two starting porphyrins. ............................................ 14


FeIIITPPS in a ratio of 2:1 and the two starting porphyrins. ........................................... 14


SnIVTPPS in a ratio of 2:1 and the two starting porphyrins............................................ 15


MnIVTPPS in a ratio of 2:1 and the two starting porphyrins. .......................................... 15

Figure 15 – TEM (a,b) and optical microscopy (c) images of LOCP + MTPPS

nanostructures. In the SEM image each grid has a side of 100 µm.............................. 16

Figure 16 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with

H4TPPS in a ratio of 4:1 and the two starting porphyrins. ............................................. 18


H4TPPS in ratios1 to 4. .................................................................................................. 19

Figure 18 – Representation of two hypothetical different aggregation conformations for

a reaction between H4TPPS (small diamond shape) and LOCP (large octahedrons) in a

2:1 ratio producing J-aggregates (right) or not (left). ..................................................... 19

Figure 19 – Representation of three hypothetical different aggregation conformations for

a reaction between H4TPPS (small diamond shape) and LOCP (large octahedrons) in a

4:1 ratio producing J-aggregates (middle and right) or not (left). .................................. 20


xi

Figure 20 – Representation of two hypothetical different aggregation conformations for

a reaction between H4TPPS (small diamond shaped) and LOCP (large octahedrons) in

a 16:1 ratio (left) and demonstrating the nanostructures in equilibrium with free porphyrin

(right). .............................................................................................................................. 20


H4TPPS in ratios 4 to 8. ................................................................................................. 21

Figure 22 – Plot showing the various H4TPPS: Porphyrin1 ratios expected and the one

obtained .......................................................................................................................... 21

Figure 23 – TEM(a) and SEM(b) images of LOCP and H4TPPS nanostructures ........ 22


CuTPPS and NiTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the

nanostructures of the reactions of LOCP with CuTPPS (1:2 ratio) or NiTPPS (1:2 ratio).

........................................................................................................................................ 25


CuTPPS and FeTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the

nanostructures of the reactions of LOCP with CuTPPS (1:2 ratio) or FeTPPS (1:2 ratio).

........................................................................................................................................ 25


CuTPPS and SnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the

nanostructures of the reactions of LOCP with CuTPPS (1:2 ratio) or SnTPPS (1:2 ratio).

........................................................................................................................................ 26


CuTPPS and MnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the

nanostructures of the reactions of LOCP with CuTPPS (1:2 ratio) or MnTPPS (1:2 ratio).

........................................................................................................................................ 26


NiTPPS and FeTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the

nanostructures of the reactions of LOCP with NiTPPS (1:2 ratio) or FeTPPS (1:2 ratio).

........................................................................................................................................ 27


NiTPPS and SnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the

nanostructures of the reactions of LOCP with NiTPPS (1:2 ratio) or SnTPPS (1:2 ratio).

Note: Reaction done at pH 1 and this results in the extra Soret band at 439 nm. ........ 27


NiTPPS and MnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the

nanostructures of the reactions of LOCP with NiTPPS (1:2 ratio) or MnTPPS (1:2 ratio).

........................................................................................................................................ 28

xii FCUP Exploring the Boundaries of Porphyrin Materials Synthesis by Ionic Self-Assembly


FeTPPS and SnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the

nanostructures of the reactions of LOCP with FeTPPS (1:2 ratio) or SnTPPS (1:2 ratio).

........................................................................................................................................ 28


FeTPPS and MnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the

nanostructures of the reactions of LOCP with FeTPPS (1:2 ratio) or MnTPPS (1:2 ratio).

........................................................................................................................................ 29


SnTPPS and MnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the

nanostructures of the reactions of LOCP with SnTPPS (1:2 ratio) or MnTPPS (1:2 ratio).

........................................................................................................................................ 29

Figure 34 – TEM images of LOCP, CuIITPPS and FeIIITPPS nanostructures at two

different magnifications. ................................................................................................. 30

Figure 35 – Structural formula of Br8TPPS .................................................................... 32

Figure 36 – Structural formula of Br8TMPyP .................................................................. 32


xiii

List of abbreviations

BIPNs Binary Ionic Porphyrin Nanomaterials

CBI Cooperative Binary Ionic

ICP-MS Inductively-coupled plasma mass spectrometry

ISA Ionic Self-Assembly

ITAPs Ionic tetraarylporphyrins

LED Light emitting diode

UV/Vis Ultraviolet/Visible Spectrophotometry

TEM Transmission Electron Microscopy

SEM Scanning Electron Microscopy

Br8TMPyP 2,3,7,8,12,13,17,18-octabromotetra(N-methyl-4-pyridyl)porphyrin

Br8TPPS 2,3,7,8,12,13,17,18-octabromotetra(4-sulfonatophenyl)porphyrin

CuIITPPS Copper (II) tetra(4-sulfonatophenyl)-porphyrin

FeIIITPPS Iron (III) tetra(4-sulfonatophenyl)-porphyrin

H4TPPS Tetra(4-sulfonatophenyl)-porphyrin dication

LOCP Large Octacationic Porphyrin

MnIIITPPS Manganese (III) tetra(4-sulfonatophenyl)-porphyrin

MTPPS Metal tetra(4-sulfonatophenyl)-porphyrin

NiIITPPS Nickel (II) tetra(4-sulfonatophenyl)-porphyrin

SbVO-TPP Oxo-antimony(V) tetraphenylporphyrin

SnIVTPPS Tin (IV) tetra(4-sulfonatophenyl)-porphyrin

SnIVTPyP Tin (IV) tetra(4-pyridyl)porphyrin

SnIVTMPyP Tin (IV) tetra(N-methyl-4-pyridyl)porphyrin

TEtOHPyP Tetra(2-hydroxyethyl-4-Pyridyl)porphyrin

TMPyP Meso-tetra(N-methyl-4-pyridyl)porphyrin

TPPS Tetra(4-sulfonatophenyl)-porphyrin

ZnIITPPS Zinc (II) tetra(4-sulfonatophenyl)-porphyrin


1

1. Introduction

1.1. Porphyrins

Porphyrins are heterocyclic macrocycles composed of four

pyrrole subunits interconnected at the α-carbon by methine

bridges. Porphyrins are aromatic, their macrocycle has 26

delocalized π electrons in total and 18 in the shortest ring

(following Hückel's rule 4n+2 for aromaticity with n=4). This

makes them highly conjugated systems and as a

consequence they usually have very intense absorption

peaks in the visible region. The most intense of these peaks

is the Soret band, usually found around 400 nm. The name

porphyrin is derived from its colour, as it comes from the Greek porphyros meaning

purple.

Porphyrins were first synthetized in the 1930´s by the German team of Hans Fischer and

Wilhelm Gleim1 and the English team of Paul Rothemund2,3, using pyrroles and

aldehydes (formaldehyde, acetaldehyde and furfural)2 to form Porphine (Figure 1), the

simplest porphyrin, and other meso substituted porphyrins. This synthesis was further

improved in the 1960’s4, and through green chemistry approaches, such as making

porphyrins using microwaves in a dry medium5 and using pyrroles and aldehydes in the

gaseous state without solvents or catalysts6.

As it was previously said, porphyrins are very conjugated systems, so they have a high

resonance energy of roughly 1670-2500 kJ mol-1 7. This makes meso-hydrogenated

derivatives such as porphodimethanes and porphyrinogens (Figure 2)

thermodynamically unfavourable and therefore porphyrins are usually quite stable. Other

common derivatives are obtained from adding two and four hydrogen atoms to the beta

position of porphyrin, originating chIorin and bacteriochlorin or isobacteriochlorin

respectively, which are also aromatic macrocycles with the same number of π electrons

in the shortest ring.

Figure 2 – From left to right structural formulas of Porphine, Porphodimethane, Porphyrinogen, ChIorin, Bacteriochlorin, lsobacteriochlorin

Np

Figure 1 – Structural formula of Porphine


1.1.1. Biological importance

In biological systems, porphyrins and related tetrapyrroles such as chlorophylls are very

important when incorporated into proteins. There, they play a central role in many

essential processes. Maybe their most important role is in the energy reactions of

advanced life, namely photosynthesis and respiration. In photosynthesis, Chlorophylls

and porphyrins are responsible for the capture of photons and the transfer of electrons,

essential to the production of energy for almost all life on earth8,9. In contrast, the

porphyrin heme contained in Cytochrome C oxidase and other enzymes are responsible

for energy production during cellular respiration10.

Porphyrins also perform other catalytic roles such as catalysis in nitric oxide synthase,

catalase, and oxygen transport and storage in the haemoglobin and myoglobin proteins.

In fact, it’s the porphyrin in haemoglobin that gives blood its red colour10.

1.1.2. Applications

Apart from their role in biological systems, porphyrins have also been used in various

technological and medical applications. In medicine, vertporphyn has been used to treat

eye macular degeneration by phototherapy11, and the presence of abnormal amounts of

porphyrins constitutes a disease called porphyria12, famous for its incidence in European

aristocracy. In the technology area, porphyrins have been used to try and simulate

photosynthesis11,12, in dye-sensitized solar cells13-15, in LEDs16, in photonic devices17 (for

information transfer with light) and optoelectronics18, as catalysts and photocatalysts for

the fixation and trans-formation of carbon dioxide19, and as potential tools for

delignification20 for the wood industry.

1.2. Porphyrin Nanostructures

There are various ways to make porphyrins self-assemble into nanostructures. Three of

the most used procedures are the reprecipitation method, coordination polymerization

and ionic self-assembly (ISA). In the reprecipitation method, one porphyrin species

dissolved in a solvent where it is soluble is quickly mixed into a much greater quantity of

solvent where it is insoluble leading to its precipitation. This method is probably the

simplest of the three and the most commonly used to produce nanostructures of a single

type of porphyrin21-24. In the coordination polymerization method, metals are used to

make the linking bridge between different porphyrins. There are 2 types, type A in which

the metal is contained in the porphyrin and where the links are between it and ligating


3

peripheral substituents of the same kind of porphyrin25, and type B were an external

metal is added to solution and serves as a link between the ligating peripheral

substituents of the porphyrin26. In ISA the soluble porphyrin ion is neutralized by an

oppositely charged porphyrin or ion. This neutralization makes the system insoluble,

leading to the formation of crystalline or amorphous solids27-30. The resulting binary

organic solids can combine different porphyrin properties and are of increased interest.

In classical ISA reactions, the main interactions that lead to aggregation are coloumbic

interactions and the fitting of the diverse secondary structure of the elements involved,

which leads to the solids being made of only the starting material in ratios only defined

by their charge30.

The ISA method is used in this work and, therefore, some structures prepared to date

with porphyrins using this technique should be enumerated to serve as a framework for

this work.

Porphyrins nanotubes/nanorods

The first porphyrin nanostructures produced by ISA, reported in 2004 by Wang et

al.31 and further investigated by others32. The ones produced by the Wang team

used H4TPPS2- and SnIVTPyP4+/5+.

Porphyrin nanofibers and nanofiber bundles

Reported in 2006 by Wang et al33, using H2TPPS4- and SbVOTPP5+.

Porphyrin four-leaf clover-like dendritic structures

Reported in 2010 by Martin et al.34 the structures are formed by various metal

combinations of TEtOHPyP4+ and TPPS4−,and resemble four leaf clovers or four

sided ninja stars that can be slightly modulated in shape by changing the metals

or altering the temperature in the reactions.

Nanosheets: First X-ray structure of a CBI solid

Made with ZnTPPS4- porphyrins and with SnTMPyP4+ a system very similar to

the one used to obtain the previous structures being the only difference a methyl

group instead of an ethyl in the Sn porphyrin. Some of this nanosheets where so

large that there was obtained a crystal large enough for X-ray crystallography,

that was the first for Cooperative Binary Ionic (CBI) solids35.

Two interesting techniques used to increase the complexity and potential uses of solids

obtained by ISA are the variation of the pH of the reaction medium, that makes it possible

to obtain various compositions and structures from the same material, or the growing of

structures on top of other structures (this works by mixing two different porphyrins,

allowing them form a structure, and then adding a solution that contains two new

porphyrins that react on top of it).


1.3. Goals of this work

Binary Ionic Porphyrin Nanomaterials

produced by ISA are relatively new. To

date studies have mainly focused on

readily available ionic tetraarylporphyrins

(ITAPs) such as TMPyP4+ and TPPS4- 36.

Therefore very little is known about ISA

reactions of Porphyrin tectons with novel

and unusual structures and properties. In

this work the limits of porphyrin ISA are

studied by trying to use an unusual Large

Octacationic Porphyrin (LOCP) (Figure 3

and Figure 4)37.

LOCP has an extended π-system of the

tetrabenzoporphyrin class, with each

benzene substituent having two extra aryl

substituents. In addition, there are also

Aryl substituents at the meso position that

contribute to a significant steric crowding

of the periphery of the porphyrin. This is

relieved by deformation of the ring into a

non-planar conformation, making the

shape of LOCP similar to a horse saddle as depicted in Figure 3. Both of these

characteristics, extension of the π-system and non-planarity might be useful for

designing a material with specific light absorption features or specific oxidation or

reduction potentials. Additionally, LOCP also has an unusually high charge when all its

substituents are protonated (8+ at pH 2, the pKa of pyridine is 5,2538) compared to

previously investigated ITAPs36.

The work with LOCP was started with no knowledge of its capacity to form any kind of

nanostructure. It could very well be that the unusual characteristics of this porphyrin

could contribute to increased stability in water, or in the solid state, either disfavouring or

favouring the formation of ionic solids precipitates. To try to increase the odds of

precipitate formation, reactions were prepared with the metal and metal-free forms of the

aforementioned well studied porphyrins (TPPS4-) (Figure 5), which have been used to

prepare several other porphyrin ionic solid complexes.

Figure 3 – Crystal structure of LOCP. Adapted from Jiang, L. et al.

Figure 4 – Structural formula of LOCP


5

The reactions with Metal complexes of

TPPS are discussed in Section 3.1. The

metals used were CuII, NiII FeIII, SnIV, MnIII

and the reactions were carried out at pH 2

to guarantee that LOCP is fully

protonated. In these reactions the Metal

TPPSs (MTPPSs) should be present as

tetraanaions (due to the toluene sulfonic

acid having a pKa of -2.8)39 (effective

charge 4-) with mostly planar macrocycles.

The reactions with H4TPPS (Figure 5)

gave very different results from the ones

with MTPPSs so they are discussed

separately in section 3.2. In these reactions, the TPPS complexes should also be a

tetraanion but because it is diprotonated in the core, due to the reaction being carried

out at pH 2 (pK3 4.99, pK4 4.7640) the charge will be 2-. Contrary to MTPPSs, this gives

rise to a very nonplanar structure for H4TPPS2- due to the steric crowding of protons in

the core of the porphyrin,41 making this reaction also exceptional as a rare example of

ionic self-assembly between two very nonplanar porphyrin tectons.

The different results obtained with H4TPPS2- are likely due to the tendency that this

porphyrin has to self-aggregate and form what are called J-aggregates at high ionic

strengths.42-44 This tendency arises from the fact that, at low pH values, this porphyrin

has four negative charges on the outside and two positive charges on the inside. This

characteristic makes it easy to form structures as the ones represented in Figure 6,

where the porphyrins stack diagonally on top of each other to form long nano-strands.

Figure 6 – From left to right, representations of: Side and top view of a monomer of H4TPPS2-, side and top view of a J-

aggregate

Figure 5 – Structural formula of H4TPPS


After gaining some understanding of the system with the two previous reactions, we tried

to take advantage of the high charge of LOCP to react it with two different MTPPSs at

the same time. If successful, this would give rise to Ternary Porphyrin Ionic Solids (the

first of their kind). This would be a very valuable addition to the portfolio of possible

different porphyrin solids, as it would be an easy way to bring close together up to three

different porphyrin for purposes such as light harvesting or catalysis.

2. Materials and Methods

2.1. Porphyrins

The porphyrins used in this work are all derived

from the basic Porphyrin in Figure 7. Details

about the substituents of each porphyrin and

other important characteristics are shown on

Table 1 (page 9).

LOCP was supplied by by Prof. Hong Wang

(University of Miami, Ohio, USA) and the other

porphyrins were purchased from Frontier

Scientific.

2.2. Solvents

NanopureTM water was used for all reactant mixtures. The pH was adjusted with

hydrochloric acid and sodium hydroxide solutions. Chloroform and trifluoroacetic acid

were used to prepare the stock solution of LOCP. A solution of 68% nitric acid

(TraceSELECT® grade) was used for ICP-MS analysis. Acetone was used to clean UV-

Vis cuvettes after every measurement to prevent contaminations. All solvents and

reagents were purchased from Sigma Aldrich.

2.3. Stock solution preparation

Note that LOCP was not soluble in 0.01 M HCl so we had to form a salt first. In order to

do this LOCP was dissolved in 1ml of chloroform. Then, two drops of trifluoroacetic acid

were added to fully protonate the porphyrin and the solution was evaporated using a

Figure 7 – Structural formula of the Porphyrin that serves as a base for the porphyrins in this work


7

rotary evaporator and vacuum dried overnight to remove the residual chloroform and

trifluoroacetic acid. It was then dissolved in 0.01M HCl for the experiment. All other

porphyrins were dissolved directly in 0.01M HCl. The stock solutions prepared had the

following concentrations: LOCP 100 µM, MTPPS 400 µM, H4TPPS 400 µM and 2 mM.

2.4. Sample preparation

Two or three different porphyrin solutions were combined in a glass vial (5 or 18 mL

capacity) using appropriate volumes to obtain the desired concentrations. The volume

was always adjusted to 2 mL and the solutions were left undisturbed and in the dark for

a week to allow the formation of precipitates. LOCP target concentration was always 40

µM except in the case of H4TPPS:LOCP high-ratio reactions where 16 µM were used to

avoid a need for stock solutions of excessively high concentration.

For example, to make the reaction solution of CuTPPS:LOCP (80:40), starting with stock

solutions 400 µM and 100 µM respectively, 0.8 mL of LOCP and 0.4 mL of CuTPPS were

mixed with 0.8 mL of 0.01 M HCl in a glass vial.

2.5. Ultraviolet/Visible Spectrophotometry (UV/Vis)

Samples were prepared by collecting 1 mL or 500 µL of the homogenised solution and

centrifuging it at 18000 g for 10 minutes in an Eppendorf microtube. The supernatant

was collected and placed in a different tube while the precipitate was re-suspended in

0.01m HCl. The supernatant and precipitate were then diluted with 0.01M HCl to allow

the analysis of the peaks of interest. UV-Vis spectra were obtained using a Shimadzu

UV-3600 Spectrophotometer. For this thesis all graphs were scaled to have a max

absorbance of 1 for better comparison between the bands.

2.6. Inductively-coupled plasma mass spectrometry (ICP-MS)

Samples were prepared by collecting 1 mL of homogenized reaction solution and

centrifuging at 18000 g for 10 minutes. The supernatant was discarded and the

precipitate was re-suspended in 1 mL of 68% nitric acid (TraceSELECT® grade). Then,

it was transferred to a Falcon tube and the volume adjusted to 5 mL by adding

NanopureTM water. Control samples were prepared by diluting 1 mL nitric acid to 5 mL

using NanopureTM water. ICP-MS samples were then taken to REQUIMTE Analysis


Laboratory in the Department of Chemistry at the Universidade Nova de Lisboa where

the analysis was performed.

2.7. Transmission Electron Microscopy (TEM)

Samples were prepared by collecting 1 mL of homogenized reaction solution and

centrifuging it at 18000 g for 10 minutes. The supernatant was discarded and the

precipitate was re-suspended in 1mL of 0.01 M HCl. Then, 10µL either from the re-

suspended precipitate or a 10X dilution (depending on the amount of precipitate), was

collected with a pipette and placed on a carbon-coated copper grid for TEM analysis.

This grid was left to dry at room temperature for one day. TEM was performed using a

HITACHI H-8100 microscope operated at 200 kV.

In some samples Energy-dispersive X-ray spectroscopy (EDX) was performed using a

ThermoNoran EDS scanner to try and determine the relative amounts of different metals

in the nanostructures.

2.8. Scanning Electron Microscopy (SEM)

Samples were prepared in a similar way to those of the TEM samples, using carbon

coated copper grids. The analysis was then performed using a FEI Quanta 400 FEG

scanning electron microscope (CEMUP, University of Porto) typically operated at 15 kV

and at 10 mm working distance. The SEM data shown are from secondary electron

images.


9

Table

1 –

Substitu

ents

and im

porta

nt p

ropertie

s o

f all p

orp

hyrin

s u

sed in

this

work

.

R

1 R

2 R

3 M

ole

cu

lar w

eig

ht

λ(ε×

10

-3) pH

2

Ch

arg

e a

t pH

2

LO

CP

Ni

16

56

.68

46

1 (1

18

,6)

8+

H4 T

PP

S

H

4H

9

30

.05

43

5 (4

09

.5)

2-

Cu

TP

PS

C

u

99

2.4

8

41

2 (2

74

.7)

4-

NiT

PP

S

Ni

98

7.6

3

40

9 (1

60

.5)

4-

Fe

TP

PS

F

e

98

4.7

2

39

4 (1

21

.6)

4-

Sn

TP

PS

S

n

10

47

.64

41

6 (5

33

.3)

4-

Mn

TP

PS

M

n

98

3.8

7

46

8 (7

7.8

) 4

-


3. Ionic Self-assembly (ISA) of Large

Octacationic Porphyrin (LOCP)

All the reactions using this porphyrin were made at pH 2 to ensure that the pyridine

groups of LOCP are completely protonated, generating the octacationic species (Figure

8).

Figure 8 – Unprotonated (left) and protonated (right) form of LOCP

3.1. ISA of LOCP with MTPPS

Previous work has shown that the charges of the porphyrin tectons control the ratios in

ITAP based nanomaterials31,33,34,45, so in this reaction a solid formula of

(LOCP)(MTPPS)2 was expected for ionic self-assembly, as MTPPS has a charge of 4-

and LOCP of 8+. The expected ratio was MTPPS:LOCP 2:1, but, to study the system

and test for ISA (where constant ratio in the solid is expected irrespective of the reactant

ratio), reactions were prepared with the reactant ratios shown in Table 2.

Table 2 – MicroMolar concentrations and ratios used in the reactions.

MTPPS:LOCP µM 40:40 80:40 120:40 160:40

Ratio 1:1 2:1 3:1 4:1

Contrary to our expectations not all the reactions formed precipitates. In fact, the yield of

the reactions varied depending on the ratios and metal used. None of the 1:1 reactions


11

gave precipitates. For the Cu and Ni Porphyrins, the 2:1 reaction was the one with the

highest yield, with very little precipitate found in the 3:1 and 4:1 reactions. For the Sn and

Mn the reverse was observed, with a very low yield for the 2:1 reaction and a growing

amount of precipitate for higher reaction ratios (3:1 and 4:1).

Note that although there was no precipitate obtained from the CuII/NiIITPPS:LOCP (ratio

3/4) reactions, the amount of unreacted porphyrin left in the supernatant, calculated

using the absorption coefficient for the unreacted porphyrins, was not as much as it

would have been expected. There was 39% and 53% CuIITPPS and 51% and 63%

NiIITPPS unreacted porphyrin for the 3:1 and 4:1 reactions, respectively. This value

should be close to 100% in all of these cases. This discrepancy might be explained by

the presence of LOCP-TPPS soluble agregates that make the TPPS porphyrins have

different absorption coefficients. More so there were extra bands in both the

supernatants that further suggest the porphyrins present are not only the unreacted

starting materials.

3.1.1. ICP–MS

Table 3 – Ratios determined by ICP-MS for the precipitates of reactions involving LOCP and various MTPPS for reactant ratios 1:1 to 4:1.

1 2 3 4

ICP-MS ICP-MS ICP-MS ICP-MS

SnIV n/a n/a 1.93 2.12

FeIII n/a 1.90 1.99 2.23

MnIII n/a n/a 2.47 2.43

CuII n/a 1.98 n/a n/a

NiII n/a n/a n/a n/a

n/a – no precipitate obtained/data not available

The compositions obtained through ICP-MS are shown in Table 3. The precipitates

obtained from the reactions of LOCP with SnIV, FeIII, NiII and CuIITPPS gave

MTPPS:LOCP ratios of approximately 2, which indicate ISA reactions. The only

exception is for the reactions with MnTPPS. Here a higher ratio of approximately 2.45 is

obtained. This suggests the presence of MnTPPS tectons with a charge of less than 4-,

as this reaction is expected to be ISA. This tectons could be MnIIITPPS(OH)(H2O)

(charge 4-, expected LOCP: MTPPS ratio 2.00) and the protonated form

MnIIITPPS(H2O)2 (charge 3-, expected LOCP:MTPPS ratio 2.66), the latter being the

dominant form as the ratio observed is closer to 2.66 than to 2.00. ICP-MS data for the

LOCP:NiIITPPS reaction was not obtained as both porphyrins contain only nickel as a

metal to be analysed.


3.1.2. UV-Vis

In all reactions, the absorption bands seen for the precipitate are broadened and either

blue (CuIITPPS) or red (all other porphyrins) shifted relative to the starting materials, but

easily identifiable (Table 4). UV-Vis spectra from the re-suspended precipitates of the

1:2 reactions are shown in Figures 10 to 14.

Table 4 – Main peaks seen in UV-Vis spectra of reactant, and precipitates from reactions of LOCP-TPPS.

LOCP (Soret) MTPPS (Main band)

Starting material 461 412 (CuII), 409 (NiII), 394 (FeIII),

416 (SnIV), 467 (MnIII)

CuIITPPS:LOCP (2) ~492 408

(3)a ~494 411

(4)a ~495 412

NiIITPPS:LOCP (2) ~500 419

(3)a ~498 410

(4)a und 409

FeIIITPPS:LOCP (2) ~500 418

(3) ~500 418

(4) ~500 418

SnIVTPPS:LOCP (2)a ~483 419

(3) ~477 417

(4) 495 417

MnIIITPPS:LOCP (2)a 470b

(3) 470b

(4) 470b

Und = Peak undetermined as it is occluded by other bands; a = trace amounts obtained; b = bands superimposed

To understand why there where low precipitate yields in the 1:1 reactions and some of

the 2:1 reactions, we analysed the SnTPPS peaks in the 1:1 and 2:1 SnIVTPPS:LOCP

reactions (Figure 9).

As the unreacted porphyrin, SnIVTPPS has a Soret band at 416 nm. In the supernatant

of the 1:1 reaction, the Soret band is at 425 nm, in the re-suspended precipitate of the

2:1 it is at 419 nm and in the supernatant of the 2:1 reaction there are two peaks, one at

418 nm and other at 426 nm. Taken together, these data seem to indicate that the

porphyrin exists in three different states: the free porphyrin (peak at 416 nm), the ionic

solid (peak at 419 nm) and a third state (peak at 425 nm) that probably arises from the

formation of a dimer between SnIVTPPS and LOCP. What may be happening in the 2:1

reaction is that half of the porphyrin is in the form of this dimer (426 nm) and the rest is

either in the unreacted form or is uncentrifugeable.


13

It was also noted that the re-suspended

precipitate of SnIVTPPS:LOCP 2:1 only

had one peak in the SnIVTPPS Soret

band region. This indicates that, although

there is a low tendency to form a

precipitate, this precipitate is relatively

stable and that the dissolution and re-

equilibration of the SnIVTPPS: LOCP

ionic solid is slow on the timescales

studied (several hours).

Our experiments were unable to explain

the differences in yields for the 2:1 – 4:1

reactions, but we think that it may be

related to different coordination

geometries in the metals of TPPSs. CuII

and NiII have coordination number 4 and

FeIII, SnIV and MnIII have coordination

numbers of 5 or 6 but are likely 6-

coordinate in 0.01 M HCl.

Figure 10 – UV-Vis spectra of the nanostructure obtained for the reaction of LOCP with CuIITPPS in a ratio of 2:1 and the two starting porphyrins.

Figure 9 – UV-Vis spectra obtained in the reaction of LOCP with SnIVTPPS in a ratio of 1:1 and 2:1 and the SnIVTPPS porphyrin.


Figure 11 – UV-Vis spectra of the nanostructure obtained for the reaction of LOCP with NiIITPPS in a ratio of 2:1 and the two starting porphyrins.

Figure 12 – UV-Vis spectra of the nanostructure obtained for the reaction of LOCP with FeIIITPPS in a ratio of 2:1 and the two starting porphyrins.


15

Figure 13 – UV-Vis spectra of the nanostructure obtained for the reaction of LOCP with SnIVTPPS in a ratio of 2:1 and the two starting porphyrins.

Figure 14 – UV-Vis spectra of the nanostructure obtained for the reaction of LOCP with MnIVTPPS in a ratio of 2:1 and the two starting porphyrins.


3.1.3. TEM

Two different kinds of material were

observed on the TEM grids obtained from

the reactions. One of them, showed in

Figure 15a, consists of nanoparticles and

nanoparticle aggregates. The other

material observed consists of micron-

sized wafers with nanoscale features,

Figure 15b. These wafers are large

enough to be seen in a dried TEM grid

through optical microscopy, Figure 15c.

However we were unable to detect them

when viewing the reaction solutions on a

glass slide. This suggests that the wafers

may form while drying on the TEM grid.

The smallest particles discernible in

Figure 15 are approximately 10 nm wide,

very small considering that the

approximate dimensions of the tectons

are 2 x 2 x 0.5 nm (for MTPPS) and 2 x 2

x 1.5 nm (for LOCP).37

Figure 15 – TEM (a,b) and optical microscopy (c) images of LOCP + MTPPS nanostructures.


17

3.2. ISA of LOCP with H4TPPS

Previous studies have observed a charge of 2- for H4TPPS in ITAP ionic solids31,46, so in

this reaction a solid formula of (LOCP)(H4TPPS)4 was expected. Earlier work showed

that H4TPPS was aggregating with LOCP at unexpected ratios, so much that we studied

reactions with ratios ranging from 1:1 to 1:63 as shown in Table 5 and Table 6.

Table 5 – Ratios and Micro Molar concentrations of Porphyrins used in the reactant solutions and determined for the precipitates of LOCP and H4TPPS for low H4TPPS/LOCP ratios

Ratio Reactant 1 2 3 4 5 6 8

Precipitate 0.68 1.85 2.96 3.7 4.5 5.33 6.59

H4TPPS:LOCP µM

Reaction 40:40 80:40 120:40 160:40

Table 6 – Ratios and Micro Molar concentrations of Porphyrins used in the reactant solutions and determined for the precipitates of LOCP and H4TPPS for high H4TPPS:LOCP ratios

Ratio R 6.3 12.5 25.1 37.6 50.1 62.7

P 5.63 10.2 16.2 23.8 29.9 38.5

H4TPPS:LOCP µM R 100:16 200:16 400:16 600:16 800:16 1000:16

All reactions gave precipitates but there was a much reduced yield for the 1:1 reaction

compared to the other low ration reactions. ICP-MS analysis of the precipitates showed

that LOCP was always almost totally incorporated into the solids (>98% of the expected

Ni present). UV-Vis data showed that the amount of H4TPPS incorporated was very

dependent on the initial reaction ratio. Experimentally determined ratios for the

porphyrins in the solid using the ICP-MS and UV-Vis data are shown in Table 5 and

Table 6.

As seen for the reactions with MTPPS, the band peaks in the precipitate are shifted

relative to the starting materials. However, in this case only the H4TPPS bands are easily

identified, as the LOCP bands are occluded by another peak as explained in the next

paragraph. In Table 7 all different positions for the peaks obtained are shown.

Table 7– Main peaks seen in UV-Vis spectra of stock solutions and in the precipitates/nanostructures of various LOCP/ H4TPPS reactions.

LOCP (Soret) H4TPPS (Soret) H4TPPS (J-aggregate)

Starting material 461 434

H4TPPS:LOCP (1) ~463 418 491

H4TPPS:LOCP (2) und ~424 486

H4TPPS:LOCP (3) und 429 489

H4TPPS:LOCP (4) und 431

491 H4TPPS:LOCP (5) und 433

H4TPPS:LOCP (6) und 433

H4TPPS:LOCP (≥8) und 434

Und = Peak undetermined as it is occluded by other bands


In the 4:1 reaction, the main absorption peaks of the precipitate are seen at 431, 491

and 704 nm (Figure 16). The first peak is in a very similar position to the H4TPPS starting

material and so we assume it arises from it. The second peak is in a position similar to

the initial position of the LOCP starting material, but its intensity is too great for that to be

the case (H4TPPS has an absorption coefficient 5 times greater and it is at a 4 times

greater molar concentration, so the peak at 490 should be around 20 times smaller than

the one at 432 nm). A more plausible explanation is the presence of H4TPPS J-

aggregates that have been shown to have peaks around 490 nm and 700 nm.42-44 This

is not the first time J-aggregates-type spectra have been seen in the UV-Vis spectra of

porphyrin Ionic solids containing H4TPPS.31,46 Resonance Raman studies47 on ITAP

nanotubes of one of those works37 show that the J-aggregate bands arise from H4TPPS

without electronic coupling from the cationic porphyrin, so the absence of observable

bands for LOCP is most likely due to their low relative intensity (this seems to be

corroborated by the presence of a shoulder in the 1:1 reaction at around 463 nm that is

more probably from LOCP).

Figure 16 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with H4TPPS in a ratio of 4:1 and the two starting porphyrins.

The 3, 2 and 1 ratio reactions seem to indicate that at lower ratios of H4TPPS:LOCP the

peak at 432nm gets gradually shifted to around 420nm and the J-aggregate peak also

changes slightly its shape (Figure 17). This can be somewhat explained by all the


19

different ways H4TPPS can interact with

LOCP, thanks to the ability of the former

to form J-aggregates. In Figure 18 we can

see two different organizational structures

for the simplest aggregations of H4TPPS

and LOCP, depending on the formation or

not of J-aggregates at a ratio of 2:1. Each

of the possible structures might contribute

to the spectra in a different way and

changes in the relative amount of different

conformations as the ratios change could

account for shifts in the peaks. Figure 19

shows other conformations that are

possible for the reactions with ratio 4. As

the amount of H4TPPS increases, this

porphyrin should have a greater tendency

to surround LOCP and make J-aggregate

arrangements as the ones depicted in

Figure 20.

Note that the structures represented in Figure 18 would need counter ions (Cl-) to reduce

the charge of LOCP to 4+ to be possible in the solid state. To study if this occurred, EDX

was performed to determine the amount of chloride ions present in the solid of the 2:1

reactions (and the 4:1 reactions as a reference point). The results were inconclusive,

likely due to contaminations of the materials with chloride ions from the HCl used in the

synthesis.

Figure 18 – Representation of two hypothetical different aggregation conformations for a reaction between H4TPPS (small diamond shape) and LOCP (large octahedrons) in a 2:1 ratio producing J-aggregates (right) or not (left).

Figure 17 – UV-Vis spectra of the nanostructure obtained

in the reaction of LOCP with H4TPPS in ratios1 to 4.


Figure 19 – Representation of three hypothetical different aggregation conformations for a reaction between H4TPPS (small diamond shape) and LOCP (large octahedrons) in a 4:1 ratio producing J-aggregates (middle and right) or not (left).

Figure 20 – Representation of two hypothetical different aggregation conformations for a reaction between H4TPPS (small diamond shaped) and LOCP (large octahedrons) in a 16:1 ratio (left) and demonstrating the nanostructures in equilibrium with free porphyrin (right).

The fact that H4TPPS forms J-aggregates is essential to explain the phenomena

witnessed in higher than 4:1 ratios. With them we can speculate that LOCP serves as a

seeding platform, neutralizing only some of the charges of the structure but enough for

it to be more stable than the unreacted porphyrin. However, and as might be expected,


21

this stabilization seems to have some

limits. In UV-Vis spectra of the reactions

with ratios between 4 and 8 there seems

to be a correlation between the relative

intensities of the bands peaking at ~430

nm and ~490, nm and the increase in

ratio. As the ratio increases the first band

also increases in intensity relative to the

other. If we consider that unreacted

H4TPPS has a band with a peak at 434

nm, we can speculate that in our spectra

the band in this region corresponds to

unreacted porphyrin and that the band at

490 nm corresponds to the J-aggregate

structure. Taking this possibility into

account, one possible explanation for the

differences in the ratio between the peaks

is that as the reaction ratio increases LOCP is being increasingly less capable of

maintaining the J-aggregates and that

these de-aggregate in an increasing

amount.

Another factor that seems to demonstrate

that LOCP doesn’t have an ever

increasing ability to stabilise J-aggregates

of H4TPPS is the greater amount of

unreacted H4TPPS as the reaction ratio

increases, depicted in Figure 22. The best

way to explain the system is considering

that there is always an equilibrium

between various forms of nanostructures

resulting from the aggregation of H4TPPS

with LOCP (where the most significant part

of H4TPPS is in a J-aggregate form) and unreacted H4TPPS. As the ratio increases, this

equilibrium tends to favour more and more the unreacted porphyrin (see Figure 20).

Note that all the representations of porphyrin structures presented in this chapter are

very simple models and are only for illustration purposes, and also that the counter ions

are not shown to keep the images simple.

Figure 21 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with H4TPPS in ratios 4 to 8.

Figure 22 – Plot showing the various H4TPPS: Porphyrin1 ratios expected and the one obtained


3.2.1. TEM

TEM and SEM images showed that the

materials obtained for the H4TPPS:LOCP

reactions were similar to those seen for

the MTPPS:LOCP reactions, consisting of

nanoparticles, nanoparticle aggregates

and micron sized wafers with nanoscale

features (Figure 20a). Yet again, these

wafers are large enough to be seen in a

dried TEM grid through optical

microscopy, and are still undetectable in

the reaction solutions. This suggests, as

previously, that either the wafers only form

while drying in a TEM grid or they have a

refractive index very close to water,

turning them invisible in solution. SEM

images of the wafers (Figure 23b) show

that in some locations there are high

amounts of densely packed and

interlocking wafers, mostly in a

perpendicular orientation to the grid

suggesting that they grow outwards from

the grid as it dries.

Figure 23 – TEM(a) and SEM(b) images of LOCP and H4TPPS nanostructures


23

3.3. ISA of LOCP with two different MTPPS

As noted in Section 3.1, each LOCP is expected to interact with 2 MTPPS in the ionic

solids it forms. This presents the opportunity to assemble 2 different MTPPS porphyrins

with LOCP to produce novel ternary ionic solids.

In these reactions with one equivalent of each porphyrin it might be expected that the

solid (LOCP)(M1TPPS)(M2TPPS) would form. However, given the reactivities of MTPPS

with LOCP observed in section 3.1. solid formulas could vary from (LOCP)(M1TPPS)2 to

(LOCP)(M2TPPS)2. The range of ratios can be represented by the formula

(LOCP)(M1TPPS)2x(M2TPPS)2-2x (0≤x≤1).

The ratio of the porphyrins in the solids can be seen in Table 8. In most reactions the

ratio obtained is effectively 2:1 as the sum of both TPPS amounts to double the amount

of LOCP. The only exceptions are the reaction with MnTPPS, in it the UV/Vis bands for

MnTPPS are in the same place as the band for LOCP and as a result the increased

amount of MnTPPS seen in the supernatant (and reduced in the solid) may be a mixture

of MnTPPS and LOCP.

Table 8 – Ratios in the precipitates from reactions of LOCP and various combinations of MTPPS. The porphyrin ratios were 1:1:1 (40µM each porphyrin)

Reactant solution Measured ratio in solid

ICP-MS UV-Vis

CuIITPPS: NiIITPPS: LOCP n/a 1a:1a:1a

CuIITPPS: FeIIITPPS: LOCP 0.97:0.96:1.00 1a:0.72:1a

CuIITPPS: SnIVTPPS: LOCP 1.08:0.59:1.00 1a:0.74:1a

CuIITPPS: MnIIITPPS. LOCP 1.35:0.43:1.00 1a:0.40:1a/b

NiIITPPS: FeIIITPPS: LOCP n/a 1a:0.81:1a

NiIITPPS: SnIVTPPS: LOCP n/a 1a:0.78:1a

NiIITPPS: MnIIITPPS. LOCP n/a 1a:0.47:1a/b

FeIIITPPS: SnIVTPPS. LOCP n/a 1a:0.71:1a

FeIIITPPS: MnIIITPPS. LOCP n/a 0.57:0.25:1a/b

SnIVTPPS: MnIIITPPS: LOCP n/a n/a

n/a = data not available; a = no porphyrin detected in the supernatant; b = not 2:1 because it is not possible to accurately determine the concentrations of LOCP and MnTPPS due to overlap of the bands

The relative reactivity of LOCP with MTTPS (Table 8) is similar to that found in the

LOCP:MTPPS (Table 3) reactions. CuIITPPS and NiIITPPS are found to bind very

strongly, as these porphyrins are never found in the supernatant. FeIIITPPS seems to

bind almost as strongly as these porphyrins as evidenced by the ICP-MS data. There is

some FeIIITPPS left in the supernatant in some cases. These differences might arise

from the ICP-MS results being collected after only 1 day of reaction and that the UV-Vis


results are from a week of reaction. The other porphyrins (SnIVTPPS/MnIIITPPS) bind to

a lesser extent but they all are included somewhat in the precipitate. This is contrary to

what is observed for the MTPPS:LOCP reaction in a 2:1 ratio where these

metalcomplexes produce very little precipitate, perhaps because there is a cooperative

binding effect in the ternary system.

The UV/Vis spectra of the precipitates are compared with the 2:1 reactions and are

shown in Figures 24 to 33. In all reactions the LOCP band has a large red-shift compared

to the starting material (as seen in section 3.1.). There are frequent overlaps of various

Soret bands for the TPPS complexes, in fact the main band for MnIIITPPS is the only one

clearly distinguishable from the others. The broad soret band of FeIIITPPS:LOCP is not

visible excepting in the FeIIITPP:MnIIITPPS:LOCP where FeIIITPPS is the dominant

species. A better comparison between the main bands and their shifts can be seen in

Table 9. The reaction NiIITPPS:SnIVTPPS:LOCP has an extra peak at 439 nm but this

can be explained by the fact that this reaction was mistakenly made at pH 1 instead of

pH 2. A similar peak was seen in a different CuIITPPS:SnIVTPPS:LOCP reaction not

shown in the graphs. This reaction was also made at pH1 but the peak disappeared at

pH 2.

EDX was performed to try and determine if both MTPPS here indeed mixed in the same

nanostructures but the results were inconclusive because of the lack of sensitivity.

Table 9 – Main peaks seen in UV-Vis spectra of reactant and in the precipitates from reactions of LOCP with M1TPPS and M2TPPS.

Und = Peak undetermined as it is occluded by other bands; a = extra band present due to the reaction being carried out at pH 1

LOCP (Soret) MTPPS (Main band)

Starting material 461 412 (CuII), 409 (NiII), 394

(FeIII), 416 (SnIV), 467 (MnIII)

CuIITPPS: LOCP (2:1) ~492 408

NiIITPPS: LOCP (2:1) ~500 419

FeIIITPPS: LOCP (2:1) und 417

SnIVTPPS: LOCP (2:1) ~472 417

MnIIITPPS: LOCP (2:1) 470

CuIITPPS: NiIITPPS: LOCP (1:1:1) ~498 416 (CuII & NiII)

CuIITPPS: FeIIITPPS: LOCP (1:1:1) ~493 412

CuIITPPS: SnIVTPPS. LOCP (1:1:1) ~496 416 (CuII & SnIV)

CuIITPPS: MnIIITPPS: LOCP (1:1:1) und 412 (CuII), 474 (MnIII)

NiIITPPS: FeIIITPPS: LOCP (1:1:1) 497 418 (NiII)

NiIITPPS: SnIVTPPS: LOCP (1:1:1) 497 416, 439a

NiIITPPS: MnIIITPPS: LOCP (1:1:1) und 418 (NiII), 470 (MnII)

FeIIITPPS: SnIVTPPS: LOCP (1:1:1) ~498 423

FeIIITPPS: MnIIITPPS: LOCP (1:1:1) und 417(FeIII), 467 (MnIII)

SnIVTPPS: MnIIITPPS: LOCP (1:1:1) ~498 418(SnIV),467 (MnIII)


25

Figure 24 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with CuTPPS and NiTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the nanostructures of the reactions of LOCP with CuTPPS (1:2 ratio) or NiTPPS (1:2 ratio).

Figure 25 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with CuTPPS and FeTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the nanostructures of the reactions of LOCP with CuTPPS (1:2 ratio) or FeTPPS (1:2 ratio).


Figure 26 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with CuTPPS and SnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the nanostructures of the reactions of LOCP with CuTPPS (1:2 ratio) or SnTPPS (1:2 ratio).

Figure 27 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with CuTPPS and MnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the nanostructures of the reactions of LOCP with CuTPPS (1:2 ratio) or MnTPPS (1:2 ratio).


27

Figure 28 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with NiTPPS and FeTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the nanostructures of the reactions of LOCP with NiTPPS (1:2 ratio) or FeTPPS (1:2 ratio).

Figure 29 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with NiTPPS and SnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the nanostructures of the reactions of LOCP with NiTPPS (1:2 ratio) or SnTPPS (1:2 ratio). Note: Reaction done at pH 1 and this results in the extra Soret band at 439 nm.


Figure 30 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with NiTPPS and MnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the nanostructures of the reactions of LOCP with NiTPPS (1:2 ratio) or MnTPPS (1:2 ratio).

Figure 31 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with FeTPPS and SnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the nanostructures of the reactions of LOCP with FeTPPS (1:2 ratio) or SnTPPS (1:2 ratio).


29

Figure 32 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with FeTPPS and MnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the nanostructures of the reactions of LOCP with FeTPPS (1:2 ratio) or MnTPPS (1:2 ratio).

Figure 33 – UV-Vis spectra of the nanostructure obtained in the reaction of LOCP with SnTPPS and MnTPPS (1:1:1 ratio) compared with the UV-Vis spectra of the nanostructures of the reactions of LOCP with SnTPPS (1:2 ratio) or MnTPPS (1:2 ratio).


3.3.1. TEM

This time only one type of material was

observed in the TEM images obtained.

These were nanoparticles and

nanoparticles aggregates very similar to

the ones obtained in the reactions of

LOCP with just one type of metal TPPS

complex. Although the lack of a definite

structure might be a problem for the

technological application of this

nanostructures the homogeneity of the

material suggests if not interacting directly

the two MTPPS should at least be in close

proximity as we see no segregation of

materials.

Figure 34 – TEM images of LOCP, CuIITPPS and FeIIITPPS

nanostructures at two different magnifications.


31

4. Conclusions

It was possible to carry out Self-assembly of LOCP and TPPS, although the reactions

studied did not perform in the way predicted for classical ionic self-assembly, as shown

in the previous chapters. If the reaction between MTPPS, H4TPPS and LOCP had

followed classical ISA rules all reaction ratios would have given precipitates with ratios

of 2:1 (MTPPS) and 4:1 (H4TPPS), with the exception of those with MnIIITPPS due to the

possibility of it having charge 3- or 4- (expected ratio between 2.66:1 and 2.00:1

respectively). In the next paragraphs the results obtained are discussed.

For the MTPPS reactions, in the 2/3/4:1 ratio reactions there was a clear division

between the behaviour of Ni/CuTPPS and Fe/Sn/MnTPPS. The former had a complete

reaction in a 2:1 ratio and forming almost no precipitate in the 3/4:1 reactions, and the

latter had the opposite behaviour, with almost no precipitate in the 2:1 reaction and

increasing amounts of precipitates in the 3/4:1 reactions. One possible explanation for

this behaviour is the differences of coordination number and geometry that each of the

metals has in the centre of the porphyrin. Ni and Cu are 4 coordinated and have a square

planar geometry that might impede the connection of additional ligands besides the

internal Nitrogen of TPPS. In contrast Mn, Sn, and Fe can be 5 or 6 coordinated and

have either square pyramidal or octahedral geometries that give them the ability to ligate

one or two extra ligands. However, the mechanism by which the axial ligands modulate

the ability of MTPPS to interact with LOCP or other MTPPS molecules in the ionic solid

to produce the observed reactivities is unknown. In the 1:1 ratios reactions there were

no precipitates whatsoever, likely due to the formation of soluble MTPPS-LOCP dimers.

Even though there were differences between various MTPPS reactions with LOCP, all

TEM images obtained revealed two different types of materials obtained, micro sheets

or nanoparticles (that form some aggregates) regardless of the metal.

The H4TPPS reactions with LOCP were clearly not classical ISA, as the solids obtained

in the reactions did not have a fixed ratio (expected to be 4:1). Instead, the solids

obtained had a ratio that was always dependent on the starting material ratio. The

reactions suggested an equilibrium between the unreacted porphyrins and the solid, the

former becoming more favoured at higher H4TPPS to LOCP ratios. Although not being

made through classical ISA, the materials observed with TEM seemed to be very similar

to the ones from the MTPPS reactions, suggesting that the most important factor for the

shape of the materials formed in this reaction is the TPPS structure and not the presence

of various metals or the way through which the porphyrins come together. This is

surprising after taking into account all the differences and the fact that the H4TPPS:LOCP


solids may not even be binary ionic solids, as counter ions should be present in the solids

at lower than 4:1 ratios and excess H4TPPS in reactions with >4:1 ratios.

In the double-metal reactions with LOCP we obtained solids with an expected 2:1 ratio.

These reactions might seem the ones having a behaviour most similar to a classical ISA

but as the reactions were only attempted in a 2:1 ratio (1 M1TPPS + 1 M2TPPS: 1LOCP)

there is not enough data to be certain. It could be that different ratios such as the ones

tried in the single MTPPS:LOCP reactions might show this reaction to be just as unusual

as those previously discussed. It should be noted that the most important element of

these reactions is that they are capable of producing precipitates in which the high

charge of a porphyrin (LOCP) is used to make it react with two different oppositely

charged porphyrins (MTPPS). Here, the TEM images reveal only a single type of material

similar to the particle and particle aggregate structures obtained for the other two types

of reactions. Of particular interest here is that there is no visible separation of materials

and so there is no obvious segregation between materials formed from MTPPS-LOCP

reactions. Note that there are no large structures which hindered attempts to use EDX

analysis to determine if the two MTPPS were actually coexisting in the same

nanostructure.

Various other reactions are being tried as follow-ups to the work discussed in this thesis.

The more clear follow-ups are the mixture of LOCP with MTPPS and H4TPPS in the

same reaction either in a competitive system (ratio 4:2:1 H4TPPS:MTPPS:LOCP) or in

an attempt to form stoichiometric solids (ratio 2:1:1 H4TPPS:MTPPS:LOCP), as this may

give us the opportunity to better understand the reactions of LOCP. Different ratios for

the two MTPPS:LOCP reaction will be used to try and determine if these reactions really

follow classical ISA or only seem that way because of the ratios used so far. Other follow-

up experiments include investigations of the ISA of two very nonplanar porphyrins,

Br8TMPyP and Br8TPPS, mixed with metal and metal free forms of TPPS and TMPyP to

study the influence of non-planarity in ISA reactions.

Figure 36 – Structural formula of Br8TMPyP Figure 35 – Structural formula of Br8TPPS


33

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