11

TO MY TO MY

PRE-PhD PUBLIC SEMINERPRE-PhD PUBLIC SEMINER

22

““Photo Physical Studies of Organized Molecular Photo Physical Studies of Organized Molecular Assemblies in Langmuir Blodgett Films”Assemblies in Langmuir Blodgett Films”

PRESENTED BY:PRESENTED BY:Syed Arshad HussainSyed Arshad HussainDepartment of PhysicsDepartment of PhysicsTripura UniversityTripura UniversitySuryamaninagar-799 130Suryamaninagar-799 130Tripura, IndiaTripura, India..

UNDER THE SUPERVISION OF:UNDER THE SUPERVISION OF:Dr. D. BhattacharjeeDr. D. BhattacharjeeLecturerLecturerDepartment of PhysicsDepartment of PhysicsTripura UniversityTripura UniversitySuryamaninagar-799 130Suryamaninagar-799 130Tripura, IndiaTripura, India

33

List of my publications:List of my publications:

1.1. “Spectroscopic Characterizations of non-amphiphilic “Spectroscopic Characterizations of non-amphiphilic 2-(4- biphenylyl)-6-phenyl benzoxazole molecules at 2-(4- biphenylyl)-6-phenyl benzoxazole molecules at the air-water interface and in Langmuir-Blodgett the air-water interface and in Langmuir-Blodgett Films”.Films”. Journal of LuminescenceJournal of Luminescence (Elsevier science)(Elsevier science) 114 (2005) 114 (2005) 197-206.197-206.

2.2. “Langmuir Blodgett Films of 9-phenyl anthracene “Langmuir Blodgett Films of 9-phenyl anthracene molecules incorporated into different matrices”.molecules incorporated into different matrices”.Spectrochimica Acta Part-ASpectrochimica Acta Part-A (Elsevier science),(Elsevier science), 61 (2005) 61 (2005) 2448-2454.2448-2454.

3.3. “Role of microenvironment in the mixed Langmuir- “Role of microenvironment in the mixed Langmuir-Blodgett films”.Blodgett films”. Journal of Colloid and Interface ScienceJournal of Colloid and Interface Science (Elsevier (Elsevier science)science)(Accepted for publication, Manuscript no. JCIS-05-1209R1)(Accepted for publication, Manuscript no. JCIS-05-1209R1)

44

Following are the published papers where I Following are the published papers where I have significant contributionhave significant contribution::

1. Spectroscopic Characterizations of the mixed Langmuir-Blodgett (LB) films of 2,2'-biquinoline molecules: evidence of dimer formation.

S.Deb, S.Biswas, S.A.Hussain and D.Bhattacharjee

Chem. Phys. Letts. 405, 323-329 (2005)

2. Ageing effect of mixed Langmuir-Blodgett film of 9-Phenyl anthracene in PMMA and SA matrices.

S. Deb, S. Biswas, S. A. Hussain and D. Bhattacharjee

Ind. J. Phys. 79 (9) 1027-1031 (2005)

3. Formation of complex films with water-soluble CTAB molecules S. Biswas, S. A. Hussain, S. Deb, R. K. Nath, D. Bhattacharjee

Spectrochimica Acta Part-A (accepted for publication)

4. Langmuir-Blodgett films of p-terphenyl in different matrices: Evidence of dimer formation

S. Deb, S. A. Hussain, S. Biswas, D. Bhattacharjee

Chem Phys. Letts. (Communicated)

55

Paper presented in national Paper presented in national seminar/symposium:seminar/symposium:

1.1. “Spectroscopic study of nonamphiphilic “Spectroscopic study of nonamphiphilic buPBD assembled onto Langmuir-Blodgett buPBD assembled onto Langmuir-Blodgett Films”.Films”.Third Regional Conference on Physics Research in Third Regional Conference on Physics Research in North East India.North East India.November 09, 2002November 09, 2002Organized by Department of Physics, Dibrugarh Organized by Department of Physics, Dibrugarh UniversityUniversity

Dibrugarh-786004, Assam, INDIADibrugarh-786004, Assam, INDIA..

2.2. “Photophysical characteristics of mixed “Photophysical characteristics of mixed Langmuir Blodgett films of PBBO Langmuir Blodgett films of PBBO molecules”.molecules”.CMDAYS-04CMDAYS-04August 25-27, 2004August 25-27, 2004Department of Physics, NEHU, Shillong-793022Department of Physics, NEHU, Shillong-793022

66

Contd….Contd….3.3. “Time dependent change in mixed Langmuir-Blodgett “Time dependent change in mixed Langmuir-Blodgett

films of 9-Phenyl Anthracene in PMMA and SA films of 9-Phenyl Anthracene in PMMA and SA matrices”.matrices”.National Symposium on Impact of Chemistry on Life and National Symposium on Impact of Chemistry on Life and Society (NSICLS)Society (NSICLS)October 1-3, 2004October 1-3, 2004Department of Chemistry, Tripura UniversityDepartment of Chemistry, Tripura UniversitySuryamaninagar-799130, TripuraSuryamaninagar-799130, Tripura

4.4. “Photophysical studies of mixed Langmuir-Blodgett “Photophysical studies of mixed Langmuir-Blodgett films of molecules mixed with two different matrices”.films of molecules mixed with two different matrices”.PANE conference - 2004PANE conference - 2004November 5 & 6, 2004November 5 & 6, 2004Department of Physics, Gurucharan CollegeDepartment of Physics, Gurucharan CollegeSilchar-788004, AssamSilchar-788004, Assam

5.5. “Pressure effect studies of mixed Langmuir-Blodgett “Pressure effect studies of mixed Langmuir-Blodgett films of 2-2/ biquinoline molecules mixed with SA films of 2-2/ biquinoline molecules mixed with SA matrix”.matrix”.50th Annual Technical session and National Conference on 50th Annual Technical session and National Conference on Current Trends of research in Science and Technology under Current Trends of research in Science and Technology under the auspices of Assam Science Societythe auspices of Assam Science SocietyJanuary 28 & 29, 2005January 28 & 29, 2005Department of Physics, Guwahati University, GuwahatiDepartment of Physics, Guwahati University, Guwahati

7

IntroductionIntroduction::► Thin films of thickness of few nanometers Thin films of thickness of few nanometers

(monolayer/ multilayer) are the source of high (monolayer/ multilayer) are the source of high expectations as being useful components in many expectations as being useful components in many practical and commercial applications such as practical and commercial applications such as sensors, detectors, optoelectronics devices and sensors, detectors, optoelectronics devices and molecular electronics devices.molecular electronics devices.

► A thin film can be deposited on a solid substrate by A thin film can be deposited on a solid substrate by various techniques. However Langmuir-Blodgett (LB) various techniques. However Langmuir-Blodgett (LB) technique is one of the most promising techniques technique is one of the most promising techniques for preparing thin films as it offers:for preparing thin films as it offers:

► (a) the precise control of the monolayer thickness, (a) the precise control of the monolayer thickness, (b) homogeneous deposition of the monolayer over (b) homogeneous deposition of the monolayer over large areas (c) the possibility to make multilayer large areas (c) the possibility to make multilayer structures with varying layer composition. (d) The structures with varying layer composition. (d) The crystal parameter & packing of the film can be crystal parameter & packing of the film can be controlled by changing various LB parameter. Also by controlled by changing various LB parameter. Also by LB technique monolayer can be deposited on almost LB technique monolayer can be deposited on almost any kind of solid substrates. any kind of solid substrates.

88

Historical Perspective:Historical Perspective: Sir Benjamin Franklin described some experiments on

spreading oil films on water surface (1774)

Lord Rayleigh showed that these films are one molecular thick

Agnes Pockel reported that oil film can be controlled by movable barrier

Irving Langmuir developed the theoritical and experimental concept (1920) (Nobel prize)

Katherine Blodgett made sequential transfer of monolayer onto solids.

H. Khun (Late 1960’s) demonstrated LB films with designated properties.

First international conference on LB films was held in 1979.

99

Scientific interest:Scientific interest:After Katherine Blodgett’s successful transfer of a monolayer from water surface to a glass plate in 1934, the scientific interest in LB films After Katherine Blodgett’s successful transfer of a monolayer from water surface to a glass plate in 1934, the scientific interest in LB films

have been intensified in recent years. have been intensified in recent years. There is much current interest in the ultra thin films fabricated by the LB technique as it offers the simplest yet the most elegant method of There is much current interest in the ultra thin films fabricated by the LB technique as it offers the simplest yet the most elegant method of

obtaining highly organized molecular assemblies which have their potential applications in sensors, optoelectronic, optical signal processing, obtaining highly organized molecular assemblies which have their potential applications in sensors, optoelectronic, optical signal processing, digital optical switching devices and as models mimicking biological membranesdigital optical switching devices and as models mimicking biological membranes..

Extensive studies on LB films have been conducted after the pioneering works of Kuhn and co-workers (late 1960’s)Extensive studies on LB films have been conducted after the pioneering works of Kuhn and co-workers (late 1960’s) Although these studies have received considerable attention, the role of ultra structure as well as domain structure and also the electrical Although these studies have received considerable attention, the role of ultra structure as well as domain structure and also the electrical

and optical properties of such films is a topic of fundamental importance.and optical properties of such films is a topic of fundamental importance.In recent year nanocrystalline films obtained by Langmuir-Blodgett technique which have a great potential towards the formation of In recent year nanocrystalline films obtained by Langmuir-Blodgett technique which have a great potential towards the formation of

nanoscale devices.nanoscale devices.Detailed investigations of LB films with different molecules are important to understand the basic physics involved in such system.Detailed investigations of LB films with different molecules are important to understand the basic physics involved in such system.

1010

Figure 1: Number of publications per year with "monolayer" in the title.

1322 in 1998

1111

Insoluble amphiphilies at the air-water interface:Insoluble amphiphilies at the air-water interface:(Ideal LB compatible material)(Ideal LB compatible material)

Amphiphilic molecule

Hydrophilic part

Hydrophobic part

Hydrophobic part:Hydrophobic part: Long hydrocarbon / Fluorocarbon chain Long hydrocarbon / Fluorocarbon chainHydrophilic part:Hydrophilic part: Polar group ( -OH, -CN, -COOH, -NH3 Polar group ( -OH, -CN, -COOH, -NH3++, -, -PO4PO4--, , (CH2) (CH2)22NHNH33

++ etc, heavy metal ion ) etc, heavy metal ion )

1212

Langmuir-Blodgett (LB) film Langmuir-Blodgett (LB) film deposition instrument ( LB APEX-deposition instrument ( LB APEX-

2000C)2000C) Go to LB troughGo to LB trough

1313

Formation of monolayer on the subphase:

The Environment

The LB trough must be installed in a clean dust – free environment.

The Subphase

Water, Mercury, glycerol are most commonly used subphase.

Preparation of Film material

Standard solution of the materials of our interest was prepared in highly volatile water -insoluble organic solvent such as chloroform, benzene etc.

1414

Formation of monolayer on the subphase(Contd…) Monolayer Spreading

Known quantity of solution was spread at the air - water interface and sufficient time was given to evaporate the solvent and then the molecule remains at the air-water interface hapazardly.

1515

SURFACE PRESSURE:SURFACE PRESSURE:

o Surface pressure () can be defined as = o -

Where o = surface tension of clean subphase

= surface tension in presence of

impurity.

Surface tension of pure water is 70 mN/m.Addition of impurity causes decrease in surface tension.In LB technique this decrease in surface tension is referred to as an increase in surface pressure i.e., numerically these two are same. The surface tension of pure water is taken as the reference level.

Thus it is possible to monitor the surface pressure as a function of the area occupied by a single molecule provided that the number of molecules deposited on the surface is known.

1616

LANGMUIR-BLODGETT LANGMUIR-BLODGETT (LB) TECHNIQUE(LB) TECHNIQUE

Enlarged form of the LB troughEnlarged form of the LB troughView LB instrument

1717

Monolayer PhasesMonolayer Phases When the molecules are first spread on the water surface, When the molecules are first spread on the water surface,

they are loosely packed and form a so-called gas phase.they are loosely packed and form a so-called gas phase. Increasing the surface pressure by compressing the barrier Increasing the surface pressure by compressing the barrier

causes a transition to a liquid phase.causes a transition to a liquid phase. Further increases in pressure bring about a last Further increases in pressure bring about a last

compressibility change that is associated to a solid phase compressibility change that is associated to a solid phase transition. Further decrease in area per molecule causes transition. Further decrease in area per molecule causes collapse of monolayer.collapse of monolayer.

Molecular area (nm2/molecule)

Su

rface

pre

ssu

re (

mN

/m)

Gas phase

Liquid phase

Solid phase

1818

Langmuir Film:Langmuir Film:The two dimensional crystalline arrangement of The two dimensional crystalline arrangement of

molecules at the air- water interface is known as molecules at the air- water interface is known as Langmuir filmLangmuir film..

Langmuir-Blodgett (LB) FilmLangmuir-Blodgett (LB) Film::When the mono- or multilayers of Langmuir films When the mono- or multilayers of Langmuir films

were transferred onto a solid substrate it is called were transferred onto a solid substrate it is called Langmuir-Blodgett (LB) film.Langmuir-Blodgett (LB) film.

Deposition of Langmuir film onto solid substrate:Deposition of Langmuir film onto solid substrate:

There are three deposition schemes commonly used There are three deposition schemes commonly used to transfer Langmuir film onto solid substrate to to transfer Langmuir film onto solid substrate to form Langmuir-Blodgett (LB) film.form Langmuir-Blodgett (LB) film.

These areThese are::

Y-Type depositionY-Type deposition

X-Type depositionX-Type deposition

Z-Type depositionZ-Type deposition

19

Langmuir-Blodgett Film DepositionLangmuir-Blodgett Film Deposition• The substrates:

– Hydrophilic• Glass and quartz• Metal plates composed of oxides of chromium, aluminium, or

tin• Silver and gold (conductive substrates)• Silicon or gallium arsenide plates (semiconductive)

– Hydrophobic• Mica, HOPG & teflon coated glass etc.

• Y-Type deposition:(up & down strokes)

Hydrophilic-hydrophilic or hydrophobic-hydrophobic interaction

20

• X-Type deposition(Down stroke)

• Z-Type deposition(Upstroke)

Hydrophilic-hydrophobic interaction (X & Z type)

21

Y, X AND Z-TYPE LANGMUIR-BLODGETT FILMS:

Y-type film on a hydrophobic surface

22

Film Investigation: Once the films are formed, several techniques can be utilized to characterize

them: Pressure-Area isotherms; provides information on the miscibility of

heterogeneous phases. Spectroscopy; provides information on the chemical composition and

nature of the aggregation on the films. UV-Vis Steady state fluoresecnce spectroscopy FTIR NMR Raman etc.

X-ray diffraction; provides insights as to the arrangement of heterogeneous films.

Microscopy; enables to get a visual representation of the film surface. AFM SEM TEM

Other parameters include changes in conductivity, pH & Temperature of sub phase, molefraction, pressure of lifting, thickness etc.…

SEM imageCA-SA mixed

LB film.

23

• Recent scientific investigations suggest that Recent scientific investigations suggest that certain non-amphiphilic molecules can also form certain non-amphiphilic molecules can also form excellent Langmuir monolayer at the air-water excellent Langmuir monolayer at the air-water interface when they are mixed with long chain interface when they are mixed with long chain fatty acids such as stearic acid (SA), Arachidic fatty acids such as stearic acid (SA), Arachidic acid (AA), or some inert polymer such as acid (AA), or some inert polymer such as Polymethyl methacrylate (PMMA) or polystyrene Polymethyl methacrylate (PMMA) or polystyrene (PSt).(PSt).

The The interesting featuresinteresting features of these molecules are: of these molecules are:– they are easily available and very easy to they are easily available and very easy to

synthesize,synthesize,– their spectroscopic and aggregating properties their spectroscopic and aggregating properties

are very much similar to their amphiphilic are very much similar to their amphiphilic counterparts,counterparts,

– these molecules are cheap and these molecules are cheap and – they can form highly stable Langmuir monolayer they can form highly stable Langmuir monolayer

at the air-water interface when incorporated into at the air-water interface when incorporated into suitable supporting matrices.suitable supporting matrices.

– Their electrical & photophysical characterizations Their electrical & photophysical characterizations are changed markedly when they are incorporated are changed markedly when they are incorporated in to the restricted geometry of LB filmsin to the restricted geometry of LB films

24

Activities of our Group:Activities of our Group:• Photophysical characterizations of Langmuir Blodgett

(LB) films of various polymeric, organic, metallo organic and other materials having interesting optical and electrical properties.

• My research work is mainly concentrated on the photophysical studies of organized molecular assemblies in mono- and multilayer Langmuir-Blodgett films.

• Studies of these materials are done by changing various parameters such as molefraction, surface pressure of lifting, thickness of the films, ageing effect etc.

• For photophysical characterizations we have used the traditional and convensional spectroscopic instruments such as UV-Vis absorption spectrophotometer (Perkin Elmer, Lambda-25) and Fluorescence spectrophotometer (Perkin Elmer, LS-55). In some cases to visualize the domain structure of the mixed LB films a traditional imaging method namely scanning electron microscopy (SEM) has been employed (model S-415A)

25

Activities of our Group:(contd….)

In my Pre-PhD research work, I have already studied the photophysical characteristics of mixed LB films of the following non-amphiphilic molecules mixed with inert fatty acid (stearic acid) & inert polymer matrix (polymethyl methacrylate).

(i) 2-(4-biphenylyl)-6-phenyl benzoxazole (PBBO) (ii) 9-Phenyl Anthracene (PA)

(iii) Carbazole (CA)

[ Recently work on two more systems have already been completed and are now in the process of communication.]

26

(i) “Spectroscopic characterizations of non-amphiphilic 2-(4-biphenylyl)-6-phenyl benzoxazole molecules at the air-water interface and in Langmuir-Blodgett films” Published in Journal of Luminescences, Elsevier science 114 (2005) 197-206

2-(4-biphenylyl)-6-phenyl benzoxazole abbreviated as PBBO a well-known oxazole derivative have intense fluorescence and are used in-

Light emitting diodes, solar energy concentrators and in thin film electro-luminescent devices [1.1, 1.2].

Ultra fast optical amplitude limit material and UV-laser dye due to their non-linear transmission property [1.3].

Photophysical characterization of non-amphiphilic PBBO molecules mixed with SA and PMMA have never been studied in Langmuir Blodgett films.

Figure:1 Molecular structure of PBBO

N

O

27

2(a) 2(b)Figures 2(a) and 2(b) represent the Isotherm characteristics of PBBO mixed with PMMA and SA respectively along with pure PMMA and SA & PBBO. The numbers denote the molefractions of PBBO in PMMA or SA. The inset shows the area per molecule versus molefraction plot.

0.0 0.1 0.2 0.3 0.4 0.50

10

20

30

BO .8 .6 .4 .2 PM

Su

rfa

ce p

ress

ure

(m

N/m

)

Area per molecule (nm2)

0.0 0.2 0.4 0.6 0.8 1.0

0.04

0.06

0.08

0.10

0.12

0.14

Are

a p

er

mo

lecu

le (

nm2

)

Mole fraction of PBBO

0.0 0.1 0.2 0.3 0.4 0.50

5

10

15

20

25

30

35

40

45

BO .8 .6 .4 .2 SA

Su

rfa

ce

pre

ssu

re (

mN

/m)

Area per molecule (nm2)

0.0 0.2 0.4 0.6 0.8 1.00.00

0.05

0.10

0.15

0.20

0.25

Are

a p

er

mo

lecu

le (

nm2 )

Molefraction of PBBO

2828

From the Isotherm characteristics of fig 2(a) From the Isotherm characteristics of fig 2(a) & 2(b) we observe that:& 2(b) we observe that:

For pure PBBO isotherm the pressure rises up to 19 For pure PBBO isotherm the pressure rises up to 19 mN/m only & repeated attempt to transfer this film mN/m only & repeated attempt to transfer this film onto quartz substrate was failed.onto quartz substrate was failed.

PBBO mixed with PMMA/SA form stable Langmuir PBBO mixed with PMMA/SA form stable Langmuir monolayer at the air-water interface.monolayer at the air-water interface.

In both the cases, the area per molecules In both the cases, the area per molecules systematically decreases with the rise in surface systematically decreases with the rise in surface pressure.pressure.

Isotherm studies as well as area per molecule Isotherm studies as well as area per molecule versus mole fraction study of PBBO (inset of 2a & versus mole fraction study of PBBO (inset of 2a & 2b) indicate either ideal mixing or complete 2b) indicate either ideal mixing or complete demixing of the binary components. demixing of the binary components.

However complete demixing of the binary However complete demixing of the binary components was revealed by UV-Vis absorption components was revealed by UV-Vis absorption study of the mixed LB films.study of the mixed LB films.

view fig 2a & 2bview fig 2a & 2b

2929

Figure 3: Schematic representation of molecular Figure 3: Schematic representation of molecular organization of PBBO molecules in the mixed LB organization of PBBO molecules in the mixed LB films.films.

30

200 250 300 350 400 450 5000.0

0.5

1.0

1.5

2.0

2.5

3.0

EtOH

0.70.6

0.5

0.40.3

0.2

0.1

MC

Inte

nsity

(a.u

.)

Wavelength(nm)200 250 300 350 400 450 500

0.0

0.5

1.0

1.5

2.0

2.5

3.0

EtOH

0.1

0.2

0.30.40.5

0.6

0.7

MCIn

tens

ity(a

.u.)

Wavelength (nm)

The absorption spectra at various molefractions of The absorption spectra at various molefractions of PBBO in both the matrices are almost similar to the PBBO PBBO in both the matrices are almost similar to the PBBO microcrystal spectrum having identical peak position. microcrystal spectrum having identical peak position.

However the absorption bands of mixed LB films are However the absorption bands of mixed LB films are red shifted and show broadened spectral profile with respect red shifted and show broadened spectral profile with respect to the PBBO solution spectrum.to the PBBO solution spectrum.

The broadening of the absorption bands accompanied The broadening of the absorption bands accompanied with the red shift in the mixed LB films of PBBO, seems to be with the red shift in the mixed LB films of PBBO, seems to be due to the formation of J-aggregatesdue to the formation of J-aggregates..

4(b)4(b)4(a)4(a)

31

300 350 400 450 500 5500.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

MC

EtOH

0.7

0.60.5

0.4

0.3

0.2

0.1

Inte

nsity

(a.u

.)

Wavelength (nm)

300 350 400 450 500 5500.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

EtOH

0.1

0.2

0.3

0.4

0.5

0.60.7

MC

Inte

nsity

(a.u

.)

Wavelength (nm)

5(a)5(a) 5(b)5(b)

The fluorescence spectra of PBBO-PMMA mixed LB films show two The fluorescence spectra of PBBO-PMMA mixed LB films show two well resolved vibrational peaks. well resolved vibrational peaks.

However the fluorescence spectra of PBBO-SA mixed LB films do However the fluorescence spectra of PBBO-SA mixed LB films do not consist of any prominent vibrational structure. In this case the not consist of any prominent vibrational structure. In this case the fluorescence spectra have distinct similarity with that of the microcrystal fluorescence spectra have distinct similarity with that of the microcrystal spectrum. spectrum.

Moreover the fluorescence spectra of the mixed LB films of PBBO Moreover the fluorescence spectra of the mixed LB films of PBBO for both the matrices show a broadened spectral profile. for both the matrices show a broadened spectral profile.

This may be due to the excimeric emission occurring from the This may be due to the excimeric emission occurring from the microcrystalline aggregates of PBBO, which is later confirmed by microcrystalline aggregates of PBBO, which is later confirmed by excitation spectroscopic studies.excitation spectroscopic studies.

32

225 250 275 300 325 350 375 400

EtOH

0.1

0.2

0.30.40.5

0.6

0.7

MC

Inte

nsity

(a.

u.)

Wavelength (nm)225 250 275 300 325 350 375 400

EtOH0.1

0.2

0.3

0.40.5

0.6

0.7

MC

Inte

nsity

(a.

u.)

Wavelength (nm)

225 250 275 300 325 350 375 400

EtOH

0.10.2

0.30.4

0.5

0.6

0.7

MC

Inte

nsity

(a.u

.)

Wavelength (nm)

225 250 275 300 325 350 375 400

EtOH

0.1

0.2

0.30.4

0.5

0.6

0.7

MC

Inte

nsity

(a.

u.)

Wavelength (nm)

7(a)7(a) 7(b)7(b)6(b)6(b)6(a)6(a)

Figure 6(a) & 6(b): Figure 6(a) & 6(b): Excitation spectra of Excitation spectra of mixed LB films of PBBO mixed LB films of PBBO in PMMA & SA in PMMA & SA respectively; Striking respectively; Striking wavelength = 380wavelength = 380

Figure 7(a) & 7(b): Figure 7(a) & 7(b): Excitation spectra of Excitation spectra of mixed LB films of PBBO mixed LB films of PBBO in PMMA & SA in PMMA & SA respectively; Striking respectively; Striking wavelength = 415wavelength = 415

Excitation spectra

3333

From the figures it is observed From the figures it is observed that:that:

The excitation spectra are almost similar The excitation spectra are almost similar irrespective of the monitoring wavelength. irrespective of the monitoring wavelength.

Moreover the excitation spectra give Moreover the excitation spectra give broadened spectral profile and support broadened spectral profile and support the various band positions of absorption the various band positions of absorption spectra.spectra.

The close similarity of the excitation The close similarity of the excitation spectra monitoring at high energy and spectra monitoring at high energy and longer wavelength band gives the longer wavelength band gives the conclusion that the broadened spectral conclusion that the broadened spectral profile of emission spectra originates due profile of emission spectra originates due to the formation of excimer in the mixed to the formation of excimer in the mixed LB filmsLB films. .

View Excitation spectraView Excitation spectra

3434

Conclusion:Conclusion:• Non-amphiphilic PBBO mixed with PMMA or SA form

excellent monolayers at the air-water interface. • Isotherm studies as well as area per molecule versus

mole fraction study of PBBO indicate either ideal mixing or complete demixing of the binary components.

• The UV-Vis absorption study of the mixed LB films of PBBO reveal the nature of complete demixing of the binary components of the sample molecules PBBO and PMMA or SA which leads to the formation of clusters or aggregates.

• Fluorescence spectroscopic studies show that excimer emission occurs from the microcrystalline aggregates of PBBO.

• Excitation spectroscopic study confirms the formation of only excimeric sites.

3535

References:References:• 1.11.1.. S. J. Bai, C. C. Wu, T. D. Dang, F.E. S. J. Bai, C. C. Wu, T. D. Dang, F.E. Arnold and D. Sakaran, Appl. Phys. Lett. 84 Arnold and D. Sakaran, Appl. Phys. Lett. 84 (2004) 1656.(2004) 1656.

• 1.2.1.2. Tania M. H. Costa, Vater Stefani, Tania M. H. Costa, Vater Stefani, Marcia R. Gallas, Naira M. Balzaretti and Marcia R. Gallas, Naira M. Balzaretti and Joao A.H. da Jornada, J. Mater. Chem. 11 Joao A.H. da Jornada, J. Mater. Chem. 11 (2001) 3377.(2001) 3377.

• 1.3.1.3. Dong Xiao, Guilan Zhang, Haiyan Wang, Dong Xiao, Guilan Zhang, Haiyan Wang, Guoqing Tang and Wenju Chen, J. Nonlinear Guoqing Tang and Wenju Chen, J. Nonlinear Opt. Phys. Mat. 93 (2000) 309.Opt. Phys. Mat. 93 (2000) 309.

• 1.4.1.4. • (i)(i) Gaines, G. L, Ed. Insoluble Monolayers Gaines, G. L, Ed. Insoluble Monolayers at Liquid-Gas Interfaces Wiley Interscience, at Liquid-Gas Interfaces Wiley Interscience, New York, 1966.New York, 1966.

• (ii).(ii). Dorfler, H. D. Adv. Colloid Interface Dorfler, H. D. Adv. Colloid Interface Sci. 31 (1990) 1Sci. 31 (1990) 1

• (iii)(iii) Barnes, G.T., J. Colloid Interface Barnes, G.T., J. Colloid Interface Sci. 144 (1991) 299. Sci. 144 (1991) 299.

36

(ii) “(ii) “Langmuir-Blodgett films of 9-phenyl Langmuir-Blodgett films of 9-phenyl anthracene molecules incorporated into anthracene molecules incorporated into

different matricesdifferent matrices”.”.(The paper is published in (The paper is published in Spectrochimica Acta Part-A , Spectrochimica Acta Part-A ,

Elsevier scienceElsevier science 61 (2005) 2448-2454). 61 (2005) 2448-2454).

• Anthracene and its derivatives have rigid molecular structure and interesting spectroscopic and photo conducting properties as well as also have high fluorescence intensity.

• Moreover the properties of these derivatives are highly sensitive to the microenvironment in which they are incorporated.

• However detailed study of 9-phenyl anthracene in various matrices have never been done before.

37

0.0 0.1 0.2 0.3 0.40

10

20

30

40

8 6 4 2 PM

Sur

face

pre

ssur

e (m

N/m

)

Area per molecule (nm2)0.0 0.2 0.4

0

10

20

30

40

8 6 4 2 SA

Su

rfa

ce p

ress

ure

(m

N/m

)

Area per molecule (nm2)

1(a) 1(b)

Figure 1(a) & 1(b): -A isotherm of PA mixed with PMMA & SA respectively, alongwith pure PMMA & SA isotherm. Number denotes corresponding molefraction. Inset shows molecular structure of PA.

3838

The isotherm characteristics (The isotherm characteristics (figure 1a & 1bfigure 1a & 1b), ), show that the area per molecule for pure show that the area per molecule for pure PMMA and SA are 0.11 nm2 and 0.225 nm2 PMMA and SA are 0.11 nm2 and 0.225 nm2 respectively at a surface pressure of 15 respectively at a surface pressure of 15 mN/m. mN/m.

Also the area per molecule decreases Also the area per molecule decreases consistently with the increase in consistently with the increase in molefraction of PA in both the matrices, molefraction of PA in both the matrices, which confirms the successful incorporation which confirms the successful incorporation of PA molecules into the mixed Langmuir-of PA molecules into the mixed Langmuir-Blodgett films.Blodgett films.

The area per molecule vs. molefraction The area per molecule vs. molefraction study (figure not given) also confirms that study (figure not given) also confirms that the PA molecules have been successfully in the PA molecules have been successfully in corporated in the mixed films which are corporated in the mixed films which are consistent with the behaviour of other non-consistent with the behaviour of other non-amphiphilesamphiphiles..

View fig 1a & 1bView fig 1a & 1b

39

200 250 300 350 400 450 500 550 600

EtOH

1

2

3

4

5

6

7

MC

EtOH1

2

3

4

5

6

7

MC

Inte

nsity

(au

)

Wavelength (nm)

Figure 2(a) & 2(b): UV-Vis absorption & steady state Figure 2(a) & 2(b): UV-Vis absorption & steady state fluorescence spectra of mixed LB films of PA in PMMA fluorescence spectra of mixed LB films of PA in PMMA & SA respectively, along with their solution and & SA respectively, along with their solution and microcrystal spectra. microcrystal spectra.

2(a)2(a) 2(b)2(b)200 250 300 350 400 450 500 550 600

MC

7

6

5

4

3

2

1

EtOH EtOH

1

2

3

4

5

6

7

MC

Inte

nsity

(a.

u.)

Wavelength (nm)

4040

From figure 2a & 2b it is observed From figure 2a & 2b it is observed that:that:

There is There is no shifting of band position of the absorption no shifting of band position of the absorption spectra of PA-PMMA mixed LB filmsspectra of PA-PMMA mixed LB films w.r.to the solution w.r.to the solution absorption spectrum. However absorption spectra of PA-SA absorption spectrum. However absorption spectra of PA-SA mixed LB films show a mixed LB films show a blue shifting for lower molefractionblue shifting for lower molefraction and and no shifting for higher molefractionno shifting for higher molefraction w.r.to the solution w.r.to the solution spectrum.spectrum.

Almost identical peak position in case of PMMA Almost identical peak position in case of PMMA matrix may be due to the formation of matrix may be due to the formation of I-type of aggregates I-type of aggregates of PA in PA-PMMA mixed LB films. of PA in PA-PMMA mixed LB films.

However in case of SA matrix simultaneous blue shifting as However in case of SA matrix simultaneous blue shifting as well as no shifting of the high energy band depending on well as no shifting of the high energy band depending on molefraction may lead to the conclusion that there is a molefraction may lead to the conclusion that there is a competition between two different types of aggregates competition between two different types of aggregates namely namely I-type and H-type play their dominant role in the I-type and H-type play their dominant role in the PA-SA mixed LB films.PA-SA mixed LB films.

The fluorescence spectra (The fluorescence spectra (figure 2a & 2bfigure 2a & 2b) of mixed LB films ) of mixed LB films of PA in both the matrices show distinct similarity with that of PA in both the matrices show distinct similarity with that of solution spectrum. Also the high energy band at 399 nm of solution spectrum. Also the high energy band at 399 nm is considerably reduced in intensity and the band at 417 is considerably reduced in intensity and the band at 417 nm is quite intense. This may be due to the nm is quite intense. This may be due to the reabsorption reabsorption effect owing to the closer association of the molecules.effect owing to the closer association of the molecules.

view fig 2a & 2bview fig 2a & 2b

41

200 250 300 350 400 450 500 550 600

S = StableR = Recent

5 (S)

1 (S)1 (S)

1 (R)

5 (R)

1 (R)

5 (S)

5 (R)

Inte

nsi

ty (

a.u

.)

Wavelength (nm)200 250 300 350 400 450 500 550 600

S = StableR = Recent

5 (S)

1 (S)

5 (R)

1 (R)1 (R)

5 (R)

5 (S)

1 (S)

Inte

nsi

ty (

au)

Wavelength (nm)

3(b)3(b)3(a)3(a)

Figure 3(a) & 3(b): UV-Vis absorption & Figure 3(a) & 3(b): UV-Vis absorption & steady state fluorescence spectra of recent steady state fluorescence spectra of recent & stable LB films of PA in PMMA & SA & stable LB films of PA in PMMA & SA respectively at two different molefractions respectively at two different molefractions of 0.1M & 0.5M.of 0.1M & 0.5M.

Ageing Effect:Ageing Effect:

4242

From the ageing effect study we observe From the ageing effect study we observe that:that:• Once multilayered LB films are deposited onto the quartz Once multilayered LB films are deposited onto the quartz

substrate, it would take several hours substrate, it would take several hours (>200 hours)(>200 hours) to get to get the film in a stable condition. the film in a stable condition.

• UV-Vis absorption spectroscopic study of recently UV-Vis absorption spectroscopic study of recently fabricated (00 h) and stable (> 200 h) LB films of PA in SA fabricated (00 h) and stable (> 200 h) LB films of PA in SA matrix give evidence of the matrix give evidence of the orientational change of orientational change of molecules from I-type to H-type aggregatesmolecules from I-type to H-type aggregates.. Where as Where as their fluorescence spectra remain almost same, suggesting their fluorescence spectra remain almost same, suggesting no translational movementno translational movement of the molecule in the mixed of the molecule in the mixed LB film of PA in SA.LB film of PA in SA.

• UV-Vis absorption spectra of recently lifted and stable PA- UV-Vis absorption spectra of recently lifted and stable PA- PMMA mixed LB films are identical in nature which PMMA mixed LB films are identical in nature which suggests no suggests no orrientational change of molecules took placeorrientational change of molecules took place. . But the fluorescence spectroscopic studies reveal that But the fluorescence spectroscopic studies reveal that recently lifted films at higher molefraction of PA (0.5M) in recently lifted films at higher molefraction of PA (0.5M) in PMMA gives a broad excimeric band whereas stable LB film PMMA gives a broad excimeric band whereas stable LB film of the same gives the well structured vibrational bands of the same gives the well structured vibrational bands which may arise due to the presence of monomeric which may arise due to the presence of monomeric species. That is with increasing species. That is with increasing time monomeric species time monomeric species gradually increases and excimeric species decreases gradually increases and excimeric species decreases suggesting a translational movement of moleculessuggesting a translational movement of molecules take take place in the PA-PMMA mixed LB films so that with the place in the PA-PMMA mixed LB films so that with the passage of time molecules move away from each other to passage of time molecules move away from each other to create monomeric sites. create monomeric sites. Fig 3(a) & 3(b)Fig 3(a) & 3(b)

43

200 250 300 350 400 450 500 550 600

30

25

20

15

30

25

20

15

Inte

nsity

(a.

u.)

wavelength (nm)

300 350 400 450

( 30P, 480 )

( 15P, 480 )

( 30P, 448 )

( 15P, 448 )

(15P, 420 )( 30P, 420 )

Intw

ensi

ty (

a.u.

)

Wavelength (nm)

Figure 4(a):Figure 4(a): UV-Vis absorption and steady state UV-Vis absorption and steady state fluorescence spectra of PA-SA mixed LB films lifted at fluorescence spectra of PA-SA mixed LB films lifted at different surface pressure of 15, 20, 25 & 30 mN/m. different surface pressure of 15, 20, 25 & 30 mN/m. Figure 4(b):Figure 4(b): Excitation spectra of PA-SA mixed LB films Excitation spectra of PA-SA mixed LB films lifted at surface pressure 15 & 30 mN/m; striking lifted at surface pressure 15 & 30 mN/m; striking wavelengths are 420, 448 & 480 nm.wavelengths are 420, 448 & 480 nm.

4(b)4(b)4(a)4(a)

4444

From the pressure effect study we observed that:From the pressure effect study we observed that:

Fluorescence spectra (Fluorescence spectra (figure 4afigure 4a) of LB film ) of LB film lifted at 25 mN/m pressure show that a lifted at 25 mN/m pressure show that a weak hump is developed at about 480 nm weak hump is developed at about 480 nm along with a prominent peak at around 450 along with a prominent peak at around 450 nm and other vibrational bands at 420 and nm and other vibrational bands at 420 and 397 nm. 397 nm.

Although the high energy band at 397 nm Although the high energy band at 397 nm is considerably reduced in intensity. At the is considerably reduced in intensity. At the higher surface pressure of 30 mN/m, 480 higher surface pressure of 30 mN/m, 480 nm band is more prominent along with 450 nm band is more prominent along with 450 nm band. Other vibrational energy bands nm band. Other vibrational energy bands are considerably reduced.are considerably reduced.

View fig 4(a)View fig 4(a) Contd…..Contd…..

4545

pressure effect studypressure effect study

contdcontd ……..…….. The excitation spectra monitoring at 420 nm and 448 nm, The excitation spectra monitoring at 420 nm and 448 nm,

in the 300-420 nm region show prominent and distinct in the 300-420 nm region show prominent and distinct vibrational bands system with identical peak position, vibrational bands system with identical peak position, prototype of absorption spectra. prototype of absorption spectra.

These bands arise due to the These bands arise due to the monomeric/excimeric sites monomeric/excimeric sites present in the LB films. present in the LB films.

However, while monitoring the band position at 480 nm, However, while monitoring the band position at 480 nm, the excitation spectra is somewhat different. The the excitation spectra is somewhat different. The vibrational bands are diffused and only a broadened band vibrational bands are diffused and only a broadened band appears at longer wavelength sides. appears at longer wavelength sides.

Especially at higher surface pressure Especially at higher surface pressure of 30 mN/m the of 30 mN/m the broadened band is shifted to 400 nm, a shift of about 11 broadened band is shifted to 400 nm, a shift of about 11 nm in comparison to longer wavelength vibrational band at nm in comparison to longer wavelength vibrational band at 389 nm. 389 nm.

Moreover this band is sufficiently broadened and other Moreover this band is sufficiently broadened and other vibrational bands are totally absent. This totally different vibrational bands are totally absent. This totally different nature of excitation spectra while monitoring at 480 nm, nature of excitation spectra while monitoring at 480 nm, definitely brings us to the conclusion that some higher definitely brings us to the conclusion that some higher order n-mers (dimer, trimer, tetramer etc.) species may order n-mers (dimer, trimer, tetramer etc.) species may exist in the LB films. exist in the LB films.

View fig 4(a) & 4(b)View fig 4(a) & 4(b)

4646

Conclusion: Conclusion: Non-amphiphilic 9-phenyl anthracene molecule Non-amphiphilic 9-phenyl anthracene molecule

when mixed with SA or PMMA forms stable when mixed with SA or PMMA forms stable Langmuir films at air-water interface and can be Langmuir films at air-water interface and can be easily transferred onto solid substrate to form easily transferred onto solid substrate to form uniform Langmuir-Blodgett films. uniform Langmuir-Blodgett films.

I-type aggregate is formed in PMMA matrixI-type aggregate is formed in PMMA matrix where as where as both I-type and H-type aggregate both I-type and H-type aggregate forms in SA matrix.forms in SA matrix.

It is also observed that It is also observed that molecular movement molecular movement exist in the recent LB filmsexist in the recent LB films and it takes about and it takes about 200 hour to aged the LB films in a stable 200 hour to aged the LB films in a stable condition. condition.

Dimmers and n-mersDimmers and n-mers are formed in the mixed LB are formed in the mixed LB films of higher mole fraction of PA in SA matrix films of higher mole fraction of PA in SA matrix and which is lifted at higher surface pressure of and which is lifted at higher surface pressure of 30 mN/m.30 mN/m.

4747

(iii) “(iii) “Role of microenvironment in the mixed Role of microenvironment in the mixed Langmuir-Blodgett filmsLangmuir-Blodgett films”.”.

(The paper is accepted by the(The paper is accepted by the Journal of Colloid and Journal of Colloid and Interface ScienceInterface Science for publication (Manuscript no. JCIS-for publication (Manuscript no. JCIS-

05-1209))05-1209))

For this work we have choosen carbazole For this work we have choosen carbazole because-because-

CA and its derivatives have intense CA and its derivatives have intense and well characterized absorption and well characterized absorption and fluorescence spectrum [3.5-3.6].and fluorescence spectrum [3.5-3.6].

Carbazole (CA) and its derivatives are Carbazole (CA) and its derivatives are used in the manufacture of organic used in the manufacture of organic photoconductors [3.1] and photoconductors [3.1] and electroluminescent devices [3.2-3.4]. electroluminescent devices [3.2-3.4].

48

0.0 0.5 1.00

10

20

30

40

50

CA

0.90.70.5

PM0.3

0.1

Su

rfa

ce

Pre

ssu

re (

mN

/m)

Area per molecule (nm 2)

0.0 0.2 0.4 0.6 0.8 1.00

10

20

30

40

50

Colla

pse

pre

ssure

(m

N/m

)

Molefractions of CA in PMMA

0.0 0.1 0.2 0.3 0.40

10

20

30

40

50

CB

0.9 0.7 0.5 0.3 0.1 SA

Su

rfa

ce p

ress

ure

(m

N/m

)

Area per molecule (nm2)

0.0 0.2 0.4 0.6 0.8 1.00

10

20

30

40

50

Col

lap

se p

ress

ure

(mN

/m)

Molefractions of CA in SA

NH

Figure 1(a) 1(b): Isotherm characteristics of CA mixed with Figure 1(a) 1(b): Isotherm characteristics of CA mixed with PMMA or SA respectively, along with pure PMMA & SA PMMA or SA respectively, along with pure PMMA & SA isotherm. Inset shows the collapse pressure vs. molefraction isotherm. Inset shows the collapse pressure vs. molefraction plot and the molecular structure of CA.plot and the molecular structure of CA.

1(a)1(a) 1(b)1(b)

4949

From the isotherm characteristics we observe that:From the isotherm characteristics we observe that:

For CA-PMMA mixed isotherm 0.3 M, the area per molecule of For CA-PMMA mixed isotherm 0.3 M, the area per molecule of mixed film is larger than that of pure PMMA. mixed film is larger than that of pure PMMA.

At 0.4 M and above area per molecule is lower than that of At 0.4 M and above area per molecule is lower than that of PMMA. PMMA.

The reason may be at lower molefractions the repulsive The reason may be at lower molefractions the repulsive interaction between unlike components in the mixed films interaction between unlike components in the mixed films predominates over a greater extent resulted in the phase predominates over a greater extent resulted in the phase separation of unlike molecules. separation of unlike molecules.

Also the predominance of this repulsive interaction at lower Also the predominance of this repulsive interaction at lower molefractions may occur due to conformational and molefractions may occur due to conformational and orientational ordering of molecules.orientational ordering of molecules.

However for both the matrices the area per molecule However for both the matrices the area per molecule gradually decreases with increasing molefractions.gradually decreases with increasing molefractions.

From the collapse pressure vs. molefraction plot it was From the collapse pressure vs. molefraction plot it was observed that the collapse pressure for all the molefraction observed that the collapse pressure for all the molefraction are almost constant and independent of molefractions of CA are almost constant and independent of molefractions of CA in both the matrices and do not match with the ideality (solid in both the matrices and do not match with the ideality (solid line) curve.line) curve.

This indicate that CA molecules and PMMA/SA molecules are This indicate that CA molecules and PMMA/SA molecules are totally immiscible in the mixed monolayer.totally immiscible in the mixed monolayer.

This immiscibility or complete demixing between CA and This immiscibility or complete demixing between CA and PMMA or SA may lead to the formation of crystalline PMMA or SA may lead to the formation of crystalline aggregates of CA molecules in the mixed LB films.aggregates of CA molecules in the mixed LB films.

view fig 1(a) & 1(b) view fig 1(a) & 1(b)

50

Figure 2: Scanning Electron Micrograph (SEM) of 10 layers of CA-SA mixed LB films (mole fraction of CA = 0.5 M) at room temperature.

Scanning Electron Microscopy (SEM) :

5151

From SEM study we observe From SEM study we observe that:that:

The aggregates with sharp and The aggregates with sharp and distinct edges correspond to the distinct edges correspond to the three dimensional aggregates of three dimensional aggregates of CA in LB films. CA in LB films.

The smooth background The smooth background corresponds to the SA matrix. corresponds to the SA matrix.

The formation of distinct The formation of distinct crystalline domains of CA, as crystalline domains of CA, as evidenced from the SEM, provides evidenced from the SEM, provides compelling visual evidence of compelling visual evidence of aggregation of CA in the LB films.aggregation of CA in the LB films.

View figure 2View figure 2

52

200 250 300 350 400 450 500

0.3

0.4

0.5

0.6

0.7

0.8

MC

0.20.1

CHCL0.1

MC

0.8

0.7

0.6

0.5

0.4

0.3

0.2

CHCL

Inte

nsity

(a.

u.)

Wavelength (nm)200 250 300 350 400 450 500

0.4

0.5

0.6

0.7

0.8

MC

0.3

0.2

0.1

CHCL

0.1

MC

0.8

0.7

0.6

0.5

0.4

0.30.2

CHCL

Inte

nsity

(a.

u.)

Wavelength (nm)

Figure 2(a) & 2(b): UV-Vis absorption & steady state Figure 2(a) & 2(b): UV-Vis absorption & steady state fluorescence spectra of CA mixed with PMMA & SA fluorescence spectra of CA mixed with PMMA & SA respectively along with the solution & microcrystal respectively along with the solution & microcrystal spectrum of CA. spectrum of CA.

3(b)3(b)3(a)3(a)

UV-Vis absorption and fluorescence spectroscopic study:UV-Vis absorption and fluorescence spectroscopic study:

5353

From the UV-Vis absorption & fluorescence From the UV-Vis absorption & fluorescence spectroscopic study we observe that:spectroscopic study we observe that:

UV-Vis absorption and steady state UV-Vis absorption and steady state fluorescence spectroscopic studies definitely fluorescence spectroscopic studies definitely conclude that CA molecules form conclude that CA molecules form microcrystalline aggregates in the mixed LB microcrystalline aggregates in the mixed LB films in case of both the matrices. films in case of both the matrices.

Fluorescence spectra of mixed LB films of CA Fluorescence spectra of mixed LB films of CA in both the matrices of PMMA and SA at in both the matrices of PMMA and SA at different molefractions reveal two different different molefractions reveal two different band systems in the longer wavelength region band systems in the longer wavelength region and in the shorter wavelength or high-energy and in the shorter wavelength or high-energy region.region.

view fig 3(a) & 3(b)view fig 3(a) & 3(b)

54

Layer effect:Layer effect:

200 250 300 350 400 450 500

0.1L05

0.5L05

0.1L25

0.5L25

0.5L05

0.5L25

0.1L25

0.1L05

Inte

nsity

(a.

u.)

Wavelength (nm)

200 250 300 350 400 450 500

0.1L25

0.5L25

0.5L05

0.1L05

0.5L25

0.1L05

0.5L05

0.1L25

Inte

nsity

(a.

u.)

Wavelength (nm)

Figure 4(a) & 4(b): UV-Vis absorption & steady state Figure 4(a) & 4(b): UV-Vis absorption & steady state fluorescence spectra of different layered mixed LB films of fluorescence spectra of different layered mixed LB films of CA in PMMA & SA respectively at two different molefraction CA in PMMA & SA respectively at two different molefraction of 0.1 & 0.2 M.of 0.1 & 0.2 M.

4(a)4(a) 4(b)4(b)

5555

No appreciable change is observed in the UV-Vis absorption No appreciable change is observed in the UV-Vis absorption spectra of the mixed LB films in both the matrices. spectra of the mixed LB films in both the matrices.

However the fluorescence spectra of CA-PMMA mixed LB However the fluorescence spectra of CA-PMMA mixed LB films show that when the number of layer is small, namely films show that when the number of layer is small, namely five, then at both the molefractions the longer wavelength five, then at both the molefractions the longer wavelength band system with prominent vibrational peaks at 397, 416 band system with prominent vibrational peaks at 397, 416 and 436 nm are quite intense in comparison to the high and 436 nm are quite intense in comparison to the high energy band. energy band.

However 25 layered LB films for both the molefractions However 25 layered LB films for both the molefractions show intense high energy bands with prominent vibrational show intense high energy bands with prominent vibrational peaks at 342 and 353 nm. and quite low intense longer peaks at 342 and 353 nm. and quite low intense longer wavelength band system. wavelength band system.

However in case of SA matrix even in case 25 layered LB However in case of SA matrix even in case 25 layered LB films, both the longer and shorter wavelength band systems films, both the longer and shorter wavelength band systems remain stronger.remain stronger.

The increase in high energy band in case of PMMA matrix at The increase in high energy band in case of PMMA matrix at higher number of layers may be due to the fact that some higher number of layers may be due to the fact that some conformational changes in CA molecules occurs in the conformational changes in CA molecules occurs in the microenvironment of PMMA matrix. As a result, deformation microenvironment of PMMA matrix. As a result, deformation in electronic structure tends to reduce.in electronic structure tends to reduce.

Moreover a comparison of the two different matrices may Moreover a comparison of the two different matrices may definitely led to the conclusion that the conformational and definitely led to the conclusion that the conformational and organizational changes of CA molecules are largely affected organizational changes of CA molecules are largely affected by the different kinds of microenvironmentby the different kinds of microenvironment in two different in two different matrices.matrices.

view fig 4(a) & 4(b)view fig 4(a) & 4(b)

56

Pressure effect:

Figure 5: Fluorescence spectra of CA/SA mixed LB films at different surface pressure of lifting at two different molefractions of 0.1 and 0.5 M of CA. The numbers denote the corresponding surface pressure of lifting and molefraction

300 350 400 450 500

0.5P150.1P20

0.5P25

0.1P30

0.5P30

0.1P25

0.5P20

0.1P15

Inte

nsity

(a.

u.)

Wavelength (nm)

5757

From the pressure effect study (figure 5) we From the pressure effect study (figure 5) we observe that:observe that:

• No appreciable change in fluorescence spectra is observed with change in pressure.

• Only at higher surface pressure of 30 mN/m and also at higher molefraction of 0.5 M the longer wavelength band system becomes intense in comparison to the high energy band.

• A comparison with the microcrystal emission spectrum of CA shows that at higher surface pressure the CA molecules in the mixed LB films organized somewhat in a large dimensional microcrystal form.

5858

From the above studies we conclude From the above studies we conclude that that ::

Carbazole molecules form an excellent Carbazole molecules form an excellent Langmuir & Langmuir-Blodgett (LB) films Langmuir & Langmuir-Blodgett (LB) films when mixed with PMMA/SA.when mixed with PMMA/SA.

The collapse pressure versus molefraction The collapse pressure versus molefraction plot of CA in PMMA/SA mixed films clearly plot of CA in PMMA/SA mixed films clearly reveals the nature of complete demixing of reveals the nature of complete demixing of the binary components in the CA-PMMA/SA the binary components in the CA-PMMA/SA mixed Langmuir films. mixed Langmuir films.

Scanning electron micrograph gives visual Scanning electron micrograph gives visual evidence of microcrystalline aggregates of CA evidence of microcrystalline aggregates of CA molecules in the mixed LB films molecules in the mixed LB films

UV-Vis absorption and steady state UV-Vis absorption and steady state fluorescence spectroscopic studies definitely fluorescence spectroscopic studies definitely conclude that CA molecules form conclude that CA molecules form microcrystalline aggregates in the mixed LB microcrystalline aggregates in the mixed LB films in case of both the matrices. films in case of both the matrices.

5959

ContdContd…..…..

Fluorescence spectra of mixed LB Fluorescence spectra of mixed LB films of CA in both the matrices of films of CA in both the matrices of PMMA and SA at different PMMA and SA at different molefractions reveal two different molefractions reveal two different band systems in the longer band systems in the longer wavelength region and in the shorter wavelength region and in the shorter wavelength or high-energy region.wavelength or high-energy region.

Fluorescence spectroscopic study of Fluorescence spectroscopic study of different number layered mixed LB different number layered mixed LB films in two different matrices reveal films in two different matrices reveal that microenvironment plays an that microenvironment plays an important role in conformational and important role in conformational and organizational changes of CA organizational changes of CA molecules in the mixed LB films.molecules in the mixed LB films.

6060

References:References: 3.1. N. Kim, E. W. Stephen, Macromolecules 18 (1985) 7413.1. N. Kim, E. W. Stephen, Macromolecules 18 (1985) 741 3.2. A. Aoki, Y. Tamagawa, T. Miyashita, Macromolecules 35 (2002) 3.2. A. Aoki, Y. Tamagawa, T. Miyashita, Macromolecules 35 (2002)

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114 (2005) 197114 (2005) 197

6161

Paper published in various reputed Paper published in various reputed journals:journals:11.. “Spectroscopic Characterizations of non-amphiphilic “Spectroscopic Characterizations of non-amphiphilic

2-(4-biphenylyl)-6-phenyl benzoxazole molecules at 2-(4-biphenylyl)-6-phenyl benzoxazole molecules at the air-water interface and in Langmuir-Blodgett the air-water interface and in Langmuir-Blodgett Films”.Films”.

S. A. HussainS. A. Hussain, S.Deb and, S.Deb and D.BhattacharjeeD.Bhattacharjee Journal of LuminescenceJournal of Luminescence, 114 (2005) 197-206., 114 (2005) 197-206.

22.. “Langmuir Blodgett Films of 9-phenyl anthracene “Langmuir Blodgett Films of 9-phenyl anthracene molecules incorporated into different matrices”.molecules incorporated into different matrices”.

S. A. HussainS. A. Hussain, S.Deb, S.Biswas, D.Bhattacharjee, S.Deb, S.Biswas, D.Bhattacharjee Spectrochimica Acta Part-ASpectrochimica Acta Part-A , 61 (2005) 2448-2454. , 61 (2005) 2448-2454.

33.. “Role of microenvironment in the mixed Langmuir- “Role of microenvironment in the mixed Langmuir-Blodgett films”.Blodgett films”.

S. A. HussainS. A. Hussain, P. K. Paul and D. Bhattacharjee , P. K. Paul and D. Bhattacharjee Journal of Colloid and Interface ScienceJournal of Colloid and Interface Science (Accepted for publication,(Accepted for publication, Manuscript no. JCIS-05-Manuscript no. JCIS-05-

1209R1)1209R1)

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Following are the published papers Following are the published papers where I have significant contribution:where I have significant contribution:

1.1. Spectroscopic Characterizations of the mixed Langmuir-Spectroscopic Characterizations of the mixed Langmuir-Blodgett (LB) films of 2,2'-biquinoline molecules: evidence Blodgett (LB) films of 2,2'-biquinoline molecules: evidence of dimer formation.of dimer formation.

S.Deb, S.BiswasS.Deb, S.Biswas,, S.A.Hussain S.A.Hussain and D.Bhattacharjee and D.Bhattacharjee Chem. Phys. Letts.Chem. Phys. Letts. 405, 323-329 (2005) 405, 323-329 (2005)

2.2. Ageing effect of mixed Langmuir-Blodgett film of 9-Phenyl Ageing effect of mixed Langmuir-Blodgett film of 9-Phenyl anthracene in PMMA and SA matrices.anthracene in PMMA and SA matrices.

S. Deb, S. Biswas, S. Deb, S. Biswas, S. A. HussainS. A. Hussain and D. Bhattacharjee and D. Bhattacharjee Ind. J. Phys.Ind. J. Phys. 79 (9) 1027-1031 (2005) 79 (9) 1027-1031 (2005)

33. Formation of complex films with water-soluble CTAB . Formation of complex films with water-soluble CTAB molecules molecules

S. Biswas, S. Biswas, S. A. HussainS. A. Hussain, S. Deb, R. K. Nath, D. , S. Deb, R. K. Nath, D. BhattacharjeeBhattacharjee

Spectrochimica Acta Part-ASpectrochimica Acta Part-A (accepted for publication) (accepted for publication)

4.4. Langmuir-Blodgett films of p-terphenyl in different matrices: Langmuir-Blodgett films of p-terphenyl in different matrices: Evidence of dimer formation Evidence of dimer formation

S. Deb, S. Deb, S. A. HussainS. A. Hussain, S. Biswas, D. Bhattacharjee, S. Biswas, D. BhattacharjeeChem Phys. LettsChem Phys. Letts.. (Communicated) (Communicated)

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Paper presented in national Paper presented in national seminar/symposium:seminar/symposium:

1.1. “Spectroscopic study of nonamphiphilic “Spectroscopic study of nonamphiphilic buPBD assembled onto Langmuir-Blodgett buPBD assembled onto Langmuir-Blodgett Films”.Films”.Third Regional Conference on Physics Research in Third Regional Conference on Physics Research in North East India.North East India.November 09, 2002November 09, 2002Organized by Department of Physics, Dibrugarh Organized by Department of Physics, Dibrugarh UniversityUniversity

Dibrugarh-786004, Assam, INDIADibrugarh-786004, Assam, INDIA..

2.2. “Photophysical characteristics of mixed “Photophysical characteristics of mixed Langmuir Blodgett films of PBBO Langmuir Blodgett films of PBBO molecules”.molecules”.CMDAYS-04CMDAYS-04August 25-27, 2004August 25-27, 2004Department of Physics, NEHU, Shillong-793022Department of Physics, NEHU, Shillong-793022

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Contd….Contd….3.3. “Time dependent change in mixed Langmuir-Blodgett “Time dependent change in mixed Langmuir-Blodgett

films of 9-Phenyl Anthracene in PMMA and SA films of 9-Phenyl Anthracene in PMMA and SA matrices”.matrices”.National Symposium on Impact of Chemistry on Life and National Symposium on Impact of Chemistry on Life and Society (NSICLS)Society (NSICLS)October 1-3, 2004October 1-3, 2004Department of Chemistry, Tripura UniversityDepartment of Chemistry, Tripura UniversitySuryamaninagar-799130, TripuraSuryamaninagar-799130, Tripura

4.4. “Photophysical studies of mixed Langmuir-Blodgett “Photophysical studies of mixed Langmuir-Blodgett films of molecules mixed with two different matrices”.films of molecules mixed with two different matrices”.PANE conference - 2004PANE conference - 2004November 5 & 6, 2004November 5 & 6, 2004Department of Physics, Gurucharan CollegeDepartment of Physics, Gurucharan CollegeSilchar-788004, AssamSilchar-788004, Assam

5.5. “Pressure effect studies of mixed Langmuir-Blodgett “Pressure effect studies of mixed Langmuir-Blodgett films of 2-2/ biquinoline molecules mixed with SA films of 2-2/ biquinoline molecules mixed with SA matrix”.matrix”.50th Annual Technical session and National Conference on 50th Annual Technical session and National Conference on Current Trends of research in Science and Technology under Current Trends of research in Science and Technology under the auspices of Assam Science Societythe auspices of Assam Science SocietyJanuary 28 & 29, 2005January 28 & 29, 2005Department of Physics, Guwahati University, GuwahatiDepartment of Physics, Guwahati University, Guwahati

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AcknowledgementAcknowledgementMy road to this place has been long and never certain. So many My road to this place has been long and never certain. So many

people have played significant roles that resulted in my arrival and people have played significant roles that resulted in my arrival and some times my survival. My gratitude is greater than my memory, so I some times my survival. My gratitude is greater than my memory, so I leave them all in my heart.leave them all in my heart.

I must acknowledge, foremost, my supervisor I must acknowledge, foremost, my supervisor Dr. D. Dr. D. BhattacharjeeBhattacharjee for his active guidance, advice, help, encouragement and for his active guidance, advice, help, encouragement and valuable suggestions. I have not envied his role at times, and I have valuable suggestions. I have not envied his role at times, and I have benefited richly for it. I believe that my greatest intellectual gains in benefited richly for it. I believe that my greatest intellectual gains in the study of physics have come directly from my involvement in this the study of physics have come directly from my involvement in this research and the discussions that we have had. From him, I have research and the discussions that we have had. From him, I have learned many writing skills and methods of presenting my thoughts so learned many writing skills and methods of presenting my thoughts so that they may be expressed concisely and clearly. that they may be expressed concisely and clearly.

I am also grateful to I am also grateful to Prof. B. K. DeProf. B. K. De, Head, Department of , Head, Department of physics, Tripura University, for his kind help and support in various physics, Tripura University, for his kind help and support in various ways.ways.

I would like to acknowledge my fellow research worker I would like to acknowledge my fellow research worker Mr. S. Mr. S. Deb, Mr. S. Biswas and Mr. P. K. Paul Deb, Mr. S. Biswas and Mr. P. K. Paul for their cooperationfor their cooperation..

I would also like to acknowledge all the I would also like to acknowledge all the research scholarsresearch scholars of the of the Atmospheric Science Research group for their nice accompany and Atmospheric Science Research group for their nice accompany and friendship.friendship.

I am also interested to acknowledge all the I am also interested to acknowledge all the staffs ofstaffs of the the department of physics for their nice cooperation. department of physics for their nice cooperation.

I would like to acknowledge my I would like to acknowledge my father and motherfather and mother, whose , whose influence is significantly related to my academic gains.influence is significantly related to my academic gains.

Finally I am grateful to Tripura University for providing me all Finally I am grateful to Tripura University for providing me all the facilities required to carryout my research work.the facilities required to carryout my research work.

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