11

Synergistic photon absorption enhancement in

Kuo-mei Chen

Department of Chemistry, NSYSU

Kaohsiung, Taiwan

OSU International Symposium on Molecular Spectroscopy

Columbus, Ohio, USA

nanostructured molecular assemblies

22

Manipulation of lightmatter interactions in plasmonic nanostructures

localized surface plasmon resonance(Adapted from Willets, Van Duyne, Annu. Rev. Phys. Chem. 58, 267 (2007))

field intensities in shaped metal nanoparticles (Adapted from Angulo, Noguez, Schatz, J. Phys. Chem. Lett. 2, 1978 (2011))

Enhanced photon absorption in plasmonic nanostructures

photovoltaics

single molecule detection

synthetic chemistry

33

Synergistic photon absorption enhancement

tdtttti It IImn

IImndt

td Imn )](],)( ),([[)]( ),0([

0 21)( HHH

IEET

Irad

I VtVt )()(H

tnm

In

Imnnmnm

Imnnm egtteeeetee

dtd

0 )()([)(

21

tdcceetge nmIradnmnm

IEETnm VgeVeg .].)(

(1)

(2)

(3)

Equation of motion of the density matrix of two adjacent molecular assemblies

Combined effects of photon-molecule interaction and electronic energy transfer (EET)

Rate of change of synergistic photon absorption after the initiation of the first photon absorption

Molecular photoabsorption enhancement under ambient solar radiation can improve efficiency substantially in renewable energy production.

44

nmIn

Imnm egttee )()(

nmIEETnm geVeg

nmIradnm eetVge )(

Synergistic dynamics (creation of entangled double excitons)

m-th n-th

m-th n-th

m-th n-th

55

The molecular mechanism of the synergistic dynamics is called a

coherence-electronic-energy-transfer-mediated (CEETRAM) photon

absorption process of nanostructured molecular assemblies.

The enhanced photon absorption process in nanostructured molecular

assemblies opens a doorway to create double excitons by incoherent

solar radiations.

66

nmImnnmnmmnnm eeteeeetee

dtd

dtd )()(

)s 1(][ 2Im))(Re(2

radWEETEET VVh

0IWrad

)()(

122

0

22 eeggradrad gVeW

)s 1()]([ 20Im))(Re()(

2IIeeee EETEET VV

ht

dtd

nmmnnm

ISPA

][ Im))(Re(2

EETEET VVh

(4)

(6)

(7)

(5)

Rate of change of synergistic photon absorption

Transition rate of one-photon absorption process

Experimental absorption cross section

Synergistic photon absorption cross section & enhancement factor

)s 1(20 ISPA

77

Experimental evidences of the synergistic photon absorption

enhancement

Nonlinear dependences of the absorption coefficient on photon flux.

At low photon fluxes, transmitted signals follow Eq. (10).

IcdlIdI )]s 1(1[ 00

fluxes)photon low(at )s 1(1 020

0 clISS

(9)

(10)

31010 ,Re2

EETV

h(8)

Beer-Lambert law

)s 1(1 020

0 clISS

88

PHOTOSYNTHETIC APPARATUS OF PURPLE BACTERIA

Adapted from Hu, Ritz, Damjanović, Autenrieth, and Schulten, Quarterly Reviews of

Biophysics, 35, 1 (2002).

Photosynthetic organisms are natural, nanostructured molecular assemblies

with an efficient EET dynamics.

99

Schematic of pigment architecture of reaction center, LH-I, and

LH-II of purple bacteria

Adapted from Humphrey, Dalke, and Schulten, J. Mol. Graphics, 14, 33

(1996).

EET (Electronic Energy Transfer)

CHARGE SEPARATION (RC Special Pair, PA and PB)

1010

Mysteries of photosynthesis

Under ambient sunlight, photon absorption rate of each chlorophyll molecule

is ~ 10 s1 (0.1 s1 at dim light level).

The optimized turnover rate of each reaction center is ~ 1000 s1.

Multiple electron-transfer reactions (METR) in photosynthetic units (PSII):

HH3C

H3C

O

O

(CH2CH=CCH2)9H

CH3

H3C

H3C

OH

OH

H

+2H+ 2e

(CH2CH=CCH2)9H

CH3

1)

plastoquinone A (Q) plastohydroquinone A (QH2)

1111

2)

H2OMncomplex

2eO + 2H+ (water oxidation, proposed mechanism)

O + O OEC O2

3)

SP+2 SP2e

METR should be completed within a short period of time (ps, ns).

Could the METR be concerted?

(proposed)

1212

Light harvesting strategy

1 reaction center + 200 bacteriochlorophyll molecules + 50

carotenoids Ultrafast, vectorial EET energy transfer to the reaction center

Not classical hopping but extonic motion

(pump-probe experiments)

Wavelike energy transfer through quantum coherence (wavepacket)

(two-dimensional electronic spectroscopy)*

*Engel, Calhoun, Read, Ahu, Mančal, Cheng, Blackenship, and Fleming, Nature, 446, 782 (2007).

Collini, Wong, Wilk, Curmi, Brumer, and Scholes, Nature, 463, 644 (2010).

1313

Absorption photometry studies on green algae (Chlorella vulgaris) in vivo

green algae in vivo (1.11107 cell mL1) NiSO4 aqueous solutions (0.192 M)

1414

PMT outputs of transmitted cw beams at 632.8 nm, green algae

(blue), Ni++ aqueous solution (red), pure water (black)

Algae cell concentrations: (A) 3.7105, (B) 6.2105, (C) 9.9105 cell mL1

1515

Experimental evidences of the synergistic photon absorption

enhancement

Nonlinear dependences of the absorption coefficient on photon flux.

At low photon fluxes, transmitted signals follow Eq. (10).

)s 1(1 020

0 clISS

1616

Photon flux dependence of the absorption coefficients of green algae in vivo

and NiSO4 aqueous solution at 632.8 nm. Ni++ solution (red, 4.2102 M),

algae (blue: 9.9105 cell mL1, black: 6.2105 cell mL1, green: 3.7105 cell

mL1)

1717

The slope of the straight line in (B) is 1.11013 Å4 ( per one algae cell

at 632.8 nm).

20

103.

1818

Summary

The molecular mechanism of the synergistic photon absorption

enhancement in nanostructured molecular assemblies is attributed to a

CEETRAM process.

The enhancement factor of green algae in vivo at 632.8 nm was

determined to be 103, consistent with the theoretical prediction.

The spatially and temporally adjacent double excitons which are

generated by the CEETRAM mechanism are quantum mechanically

entangled.

The two qubit quantum state is robust and can execute quantum

algorithm when searching for the most efficient route to reach the

reaction center in photosynthetic organisms.

The CEETRAM mechanism dictates that multiple electron transfer

reactions of quinone reduction and water oxidation in photosynthesis

are concerted.

1919

Functionally designed, nanostructured molecular assemblies can

exhibit synergistic photon absorption enhancement under

incoherent solar radiations by the CEETRAM mechanism, and

should contribute significantly to the renewable energy

production, be it synthetic or hybrid apparatuses.

2020

Acknowledgements

NSC and National Sun Yat-sen University for financial supports.

Co-workers

Dr. Yu-wei Chen

Mr. Ting-fong Gao