1Nagoya University

http://qc.chem.nagoya-u.ac.jp

1

2Universität Regensburg

PACCON 2013

Bangsaen Beach, Chon Buri, Thailand

January 24, 2013

Origin of theSize-Dependent Fluorescence

Blueshift in [n]Cycloparaphenylene

Stephan Irle,1Cristopher Camacho,1 Thomas Niehaus,2Kenichiro Itami1

2Electron Dynamics in Complex Systems Group,

Universität Regensburg

1Quantum Chemistry of Complex Systems,

Nagoya University

2

[n]Cycloparaphenylenes (Collaboration with Itami Group)

We have a dream:

Omachi, Matsuura, Segawa, Itami, Angew. Chem. Int. Ed. 49, 10202 (2011)

Prof. Itami

Ground state PES

3Segawa, Omachi, Itami, Org. Lett. 12, 2262 (2010) (Supporting Material)

Linear relationship between strain energy and size n

q

Similar to carbon nanotubes!cf. Kudinet al., Phys. Rev. B61,

235406 (2001)

Absorption and Emission Spectra

4Iwamoto, Watanabe, Sakomoto, Suzuki, Yamago, JACS 133, 8354 (2011)

Blueshift in emission

with increasing n!

Absorption and Emission Spectra

5

“Nomal” redshift in open-polyparaphenylenes

TD-CAM-B3LYP/SV(P)

Biphenyl p-MOs

6

Constant amplitude, a+2b

Constant amplitudes, a-2b

2ba

HOMO = -

LUMO = +

p-bond!

CPP frontier MO’s

• MO level diagram n=12, D6d symmetry:

• HOMO-LUMO excitation is symmetry-forbidden!

• e MOs behave like x and y functions

• LUMO+1HOMO and LUMOHOMO-1 excited states are both of

E1 symmetry, they mix!

• 4 states:

e1

a2

a1

e1LUMO+1

LUMO

HOMO

HOMO-1x y HOMO-2

LUMO+2

nodal plane

(LUMO+1xHOMO)+(LUMOHOMO-1x)

(LUMO+1yHOMO)+(LUMOHOMO-1y)

(LUMO+1xHOMO)-(LUMOHOMO-1x)

(LUMO+1yHOMO)-(LUMOHOMO-1y)

1E1

2E1 7

e

Bright!

Dark!

[n]CPP frontier MO’s

8

CAM-B3LYP/SV(P) at ground state optimized structures (all alternating conformations)

No Blue-shift inbright

transitions!

HOMO-LUMO gap increasing with increasing n!

9

[n]cPP: [2n]cPP cut in half, fixed geometry

[n]CPP frontier MO’s

[n]OPP: [2n]cPP cut in half but linear, optzd.

HOMO-LUMO gap in [3]OPP

Stronger p-antibonding

Stronger p-bonding

in [n]CPP

[∞] OPP HOMO

CAM-B3LYP/SV(P) @ S0opt’d geometries

[∞] OPP LUMO

10

Energy [eV]

1A1

21E1

11E1

1A’1A’

Qq

2 1Bx

-Qq

1 1Bx

3 1By

4 1By

2 1By

1 1By

3 1Bx

4 1Bx

Qq = x2-y2

-Qq= -(x2-y2)

Jahn Teller Energy Diagram (schematic)

11

Jahn Teller DistortionCoordinates Qe&Qq

nodal plane

-Qq = -x2+y2Qe = xy

[10]CPP

Absorption and Emission Spectra

12

1E1

Absorption: 1 peak

Emission: at least 2 intensive peaks!

Absorption and Emission Spectra

13

1E1

Absorption: 1 peak Emission: at least 2 peaks!

S0

S0’

S1

S1’

S0, S0’: ground state

S1, S1’: lowest excited singlet stateene

rgy / h

art

ree

coordinate

Energy diagram Method

TURBOMOLE, GAMESS, DALTON

B3LYP/SV(P) level

sequence of calculations

1. optimization in the ground state

2. TD-DFT calculation at S0 structure

3. optimization in the excited state

TD-DFT calculation at S1’ structure

1

2

absorption

3

fluorescence

TD-DFT Methods

14

Geometry optimization in excited state

Ground state geometries

15Segawa, Omachi, Itami, Org. Lett. 12, 2262 (2010)

2 local conformers:

Many conformational isomers …

[12]CPP [12]CPP [12]CPP

[kcal/mol]

B3LYP/6-31G(d)

Ground state PES

16Segawa, Omachi, Itami, Org. Lett. 12, 2262 (2010)

Ground state transition states for phenyl group rotation around f

[12]CPP

B3LYP/6-31G(d)f

f

[n]CPP UV/Vis spectra

17

Absorption: red

Emission: red

18

[n]CPP UV/Vis spectra

Absorption: artificially constant

Emission: still red

19

[n]CPP UV/Vis spectra

Absorption: ~constant

Emission: ~constant

20

[n]CPP UV/Vis spectra

Absorption: ~constant

Emission: ~constant

21

[n]CPP UV/Vis spectra

1E1

Absorption: ~constant

Emission: ~constant

Alternative to DFT: Approximate DFT

Density-Functional Tight-Binding: Method using atomic parameters

from DFT (PBE, GGA-type), diatomic repulsive potentials from B3LYP

•Seifert, Eschrig (1980-86): minimum

STO-LCAO; 2-center approximation

•Porezag, Frauenheim, et al. (1995):

efficient parameterization scheme: NCC-

DFTB

•Elstneret al. (1998): charge self-consistency: SCC-DFTB

•Köhleret al. (2001): spin-polarized DFTB: SDFTB

Marcus Elstner

ChristofKöhler

Helmut

EschrigGotthard

SeifertThomas

Frauenheim

22

MD in excited state

Thomas

Niehaus

Linear response:

TD-DFTB

23

CAM-B3LYPTD-DFTB/MD

Electron Dynamics in Complex Systems Group,

Universität Regensburg

Linear response

TD-DFTB:

Thomas Niehaus

Method

TD-DFTB w/mio-1-1 parameters

8 states considered, dynamics performed for S0, S1, S2/S3

MD:

1. starting from optimized geometries

2. NVT 0.5 ps equilibration at 298 K

3. NVE for 4.7 ps, production runs

4. CAM-B3LYP/SV(P) single point excited state calculations

(up to 32 sample points)

24

Simulated [n]CPP UV/Vis spectra

CAM-B3LYP/SV(P)TD-

DFTB-MD snapshots

Energy

Energy

Yes blueshift!

Yes blueshift!

Yes blueshift!

25

PESs during excited state dynamics

f-fdihedral angle

S2

S1

S0

S2-S0

S1-S0

S2

S1

S0

S2-S0

S1-S0

State energies during MD

CAM-B3LYP/SV(P)TD-DFTB-MDTransition energies during MD

26

PESs during excited state dynamics

State energies during MD Transition energies during MD

CAM-B3LYP/SV(P)TD-DFTB-MD

27

Why Emission from S2?

Energy difference between S1 and S2 very small, around

1 eV or smaller. Higher population of S2 than in usual

organic molecules.

Vibronic coupling matrix elements between S2 (u-type

symmetry) and S0/S1 (g-type symmetry) since low energy

molecular vibrations of circles behave as x2, y2 (g-type)

radiationless decay from S2 “blocked”

Consequence:

-Emission from S2 easily possible in case of large n,

while small CPP with ndistort also in x,y and emission

becomes possible from S1.

-Red shift for small n> red shift for large n

appearance of “blue shift” with increasing size n

Published in: C. Camacho, Th. Niehaus, K. Itami, SI, Chem. Sci. 4, 187 (2013)

ggu

Absorption and Emission Spectra Explained

28

Absorption: 1 peak

Dynamic blue-

shift, emission from

S2/S3

Static blue-shift,

emission from S1

Prof. Dr. Stephan Irle

sirle@chem.nagoya-u.ac.jp

Assist. Prof. Dr. Daisuke Yokogawa

d.yokogawa@chem.nagoya-u.ac.jp

WPI-Institute of Transformative Bio-Molecules &

Department of Chemistry, Nagoya University

of Complex Systems

November 5, 2012

Back row: Yoshifumi Nishimura (D3), KosukeUsui (M2), Jun Kato (B4), Tim Kowalczyk (JSPS,

PhD,), Cristopher Camacho-Leandro (PhD), Yoshio Nishimoto (JSPS, D1)

Front row: Takayo Noguchi (secty), Naoto Baba (B4), Matt Addicoat (JSPS, PhD), SI, Arifin (G30,

D1), Daisuke Yokogawa (Assist. Prof.)

OUR GOAL is to develop “transformative bio-molecules”, innovative functional

molecules that make a marked change in the form and nature of biological science and

technology.

Institute of Transformative Bio-

Molecules (Nagoya University)

EXPECTED OUTCOME

Our ten-year campaign will culminate in a wealth

of synthetic bio-molecules that will be key to

solving urgent problems at the interface of

chemistry and biology. The innovation in

food/biomass production, optical technologies,

and generation of new bio-energy can be

imagined as our dream.

THE IDENTITYof the Center is its capability to

synthesize completely new bio-functional

molecules with carefully designed functions.

OUR UNIQUE APPROACH is to apply our

cutting-edge synthesis (molecule-activation

chemistry), with the support of computational

chemistry, to synthesize key molecules to explore

advanced systems biology in plants and

animals.

Several Postdoc positions open at the WPI!

2 positions in my group, specialty: biofluorescence, binding free

energies (advertized on CCL.net)

Institute of Transformative Bio-

Molecules (Nagoya University)

33

Promotion

http://admissions.g30.nagoya-u.ac.jp

Undergraduate and Graduate Courses in Physics,

Chemistry, and Biology in ENGLISH!

Admissions for 2013 are currently ongoing.

Nagoya University Toyota Auditorium

JR Towers

Nagoya Castle

Thank you for your attention!

34