1 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

2  Manipulation of light  matter 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

3  Synergistic photon absorption enhancement (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.

4  Synergistic dynamics (creation of entangled double excitons) m-th n-th m-th n-th m-th n-th

5  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.

6 (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

7  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). (9) (10) (8)  Beer-Lambert law

8 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.

9 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, P A and P B )

10 Mysteries of photosynthesis  Under ambient sunlight, photon absorption rate of each chlorophyll molecule is ~ 10 s  1 (0.1 s  1 at dim light level).  The optimized turnover rate of each reaction center is ~ 1000 s  1.  Multiple electron-transfer reactions (METR) in photosynthetic units (PSII): (CH 2  CH=C  CH 2 ) 9 H CH 3 +2H + 2e2e (CH 2  CH=C  CH 2 ) 9 H CH 3 1) plastoquinone A (Q) plastohydroquinone A (QH 2 )

11 2) H2OH2O Mn complex 2e2e O + 2H + (water oxidation, proposed mechanism) O + O OEC O2O2 3) SP +2 SP 2e2e  METR should be completed within a short period of time (ps, ns).  Could the METR be concerted? (proposed)

12 Light harvesting strategy  1 reaction center 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).

13  Absorption photometry studies on green algae (Chlorella vulgaris) in vivo green algae in vivo (1.11  10 7 cell mL  1 ) NiSO 4 aqueous solutions (0.192 M)

14  PMT outputs of transmitted cw beams at nm, green algae (blue), Ni ++ aqueous solution (red), pure water (black) Algae cell concentrations: (A) 3.7  10 5, (B) 6.2  10 5, (C) 9.9  10 5 cell mL  1

15  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).

16  Photon flux dependence of the absorption coefficients of green algae in vivo and NiSO 4 aqueous solution at nm. Ni ++ solution (red, 4.2  10  2 M), algae (blue: 9.9  10 5 cell mL  1, black: 6.2  10 5 cell mL  1, green: 3.7  10 5 cell mL  1 )

17  The slope of the straight line in (B) is 1.1  Å 4 ( per one algae cell at nm).    10 3.

18 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 nm was determined to be 10 3, 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.

19  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.

20 Acknowledgements NSC and National Sun Yat-sen University for financial supports. Co-workers Dr. Yu-wei Chen Mr. Ting-fong Gao