Miyasaka Laboratory Yusuke Satoh

1. Application of transient anisotropy measurement to direct detection ofexcitation energy migration in the same kind of molecules H. S. Cho et al. Journal of American Chemical Society, 2003, vol.125, P5849-5860 Y. Nakamura et al. Journal of American Chemical Society, 2005, vol.127, P236-246 Miyasaka Laboratory Yusuke Satoh

2. Photosynthesis hu 6H2O + 6CO2 →　C6H12O6 + 6O2 hu Reaction Center Sun e- Light-harvesting antenna Photosynthesis is origin of most of our foods and energies. Excitation energy transfer Subsequent chemical reaction Scheme a. Photosynthesis system

3. Light-harvesting system LHⅠ,LHⅡ : Light-harvesting antenna RC:Reaction Center Scheme b. Light-harvesting system Light-harvesting system has a very beautiful structure that is arranged to achieve an excellent efficiency.

4. Artificial molecular system of photosynthesis Purpose of construction light-harvesting antenna molecules ・To construct artificial photosynthetic systems by mimicking natural systems. ・The comprehensive understanding of the relation between the structure and the functionality in the natural antenna systems

5. Contents • Introduction What’s the Light-harvesting system? How to evaluate high efficiency function of artificial 　　 molecular. • Results and Discussion The effects of the inter-chromophore distance, angles, and the kinds of chemical bonds, on the energy transfer rates • Summary

6. Principle of anisotropy measurement Polarized excitation →Production of excited molecules along with polarized light Difference of the number of the excited states along with X and Y axis transient anisotropy Time profile of transient anisotropy ● Rotational defusion （rotational motion of the excited molecules in fluid solution） ● Excitation migration hopping or charge hopping Polarized light Z X Y Hopping Rotation

7. Time-resolved fluorescence anisotropy Polarized excitation I// Detector I┴ Sample ・Time-resolved fluorescence anisotropy system ・Time-resolved fluorescence anisotropy ・・・1 I//(t)・・・parallel I┴(t)・・・perpendicular

8. Transient absorption anisotropy measurement ・Transient absorption anisotropy measurement system ・Transient absorption anisotropy DA//(t)・・・parallel DA┴(t)・・・perpendicular ・・・2

9. Articles 1. Excitation Energy Transport Processes of Porphyrin Monomer, Dimer, Cyclic Trimer, and Hexamer Probed by Ultrafast Fluorescence Anistropy Decay H. S. Cho et al. J. Am. Chem. Soc. (2003), vol.125, 5849-5860 2. Directly meso-meso Linked Porphyrin Rings: Synthesis, Charcterization, and Efficient Excitation Energy Hopping Y. Nakamura et al. J. Am. Chem. Soc. (2005), Vol.127, 236-246

10. Structures of porphyrin arrays • Excitation Energy Transport Processes of Porphyrin Monomer, Dimer, Cyclic Trimer, and Hexamer Probed by Ultrafast Fluorescence Anistropy Decay o-dimer m-trimer hexamer

11. Absorption and Fluorescense spectra B-band: Red-shifted absorption peak because of stronger interaction Q-band: Absorption peak doesn’t shift because of weaker interaction.

12. Energy hopping process khop kf P2 khop P1 P3 khop P6 P5 P4 ・・・3 khop:Energy hopping rate [P１]、[P２]、[P３]・・・concentration of excited porphyrin P1, P2, P3・・・ Scheme c. Energy hopping process of hexamer

13. Time-resolved S2 (B-band) fluorescence anisotropy The anisotropy decays of the o-dimer m-trimer and hexamer can be expressed by three components: Table a. The anisotropy decays of the o-dimer m- trimer and hexamer (B-band) For a ring structure without disorder, the analytical depolarization time was obtained by Leegwater. N:Number of hopping sites tdep:depolarization time,thop:hopping time Figure 7. Anisotropy decay profiles of the B-band emission following 405-nm photoexcitation of the monomer, o-dimer, m-trimer, and hexamer from top to bottom. ・・・4

14. Time-resolved S1 (Q-band) fluorescence anisotropy Two decay components t1:to arise from the Excitation energy transfer(EET) between porphyrin moieties in the Q-state t2:rotational diffusion dynamics thop:Energy hopping rate Table b. The anisotropy decays of the o-dimer m- trimer and hexamer (Q-band) Figure 8. Anisotropy decay profiles of the Q-band emission following 580-nm photoexcitation of the o-dimer, m-trimer, and hexamer from top to bottom.

15. Comparison of S2 hopping rate and S1 hopping rate Table c. Hopping time obtained by fluorescence anisotoropy The hopping rates in the B-band is faster than in the Q-band, because interaction between porphyrin units in the B-band is stronger than those in the Q-band.

16. Förster model and Dexter model Förster model Dexter model Förster model Energy transfer by dipole-dipole interaction Dexter model Through-bond interactions arising from p-conjugation R・・・Distance between porphyrin unit

17. Discussion n :the refractive index of the solvent, R :the center-to-center distance between the energy donor and acceptor, t :the fluorescence lifetime of the energy donor, k :the dipole-dipole orientation factor, J¢ :the spectral overlap integral, F(n) :the normalized fluorescence spectrum of the energy donor, e(n) : the absorption spectrum of the energy acceptor Table d. The calculated energy hopping rates by Förster equation

18. Discussion ・o-dimer and hexamer through-space (Förster-type) dipole-dipole interaction ・m-trimer the electronic communication contribution through phenyl groups induced by p-electronic conjugation (through-bond(Dexter-type) interaction) is required Table e. The energy hopping rates by anisotropy decay and the calculated energy hopping rates by Förster equation

19. Structures of porphyrin rings 2. Directly meso-meso Linked Porphyrin Rings: Synthesis, Charcterization, and Efficient Excitation Energy Hopping Character： Porphyrin arrays is cyclic structure

20. Absorption and Fluorescense spectra Figure 6. Fluorescence spectra of CZ4, CZ6, and CZ8 taken for excitation at 455 nm in THF. Figure 5. Absorption spectra of porphyrin arrays in THF; (b) CZ4, CZ6, and CZ8. The broad and structureless Soret bands indicate that there are some heterogeneities in dipole-dipole coupling between the porphyrin units.

21. Transient absorption of porphyrin rings Table d. Two decay components t1: S1-S1 annihilation time t2: S1 lifetime The pump-power dependence on the transient absorption decay is indicative of the S1-S1 annihilation process. the S1-S1 annihilation process should be a direct evidence of the Förster-type incoherent excitation energy transfer process within the cyclic array. Figure 9. Transient absorption decay profiles of CZ4, CZ6, and CZ8 that include pump-power dependences in THF, where the pump and probe wavelengths are 583 and 460 nm.

22. Transient absorption anisotropy of porphyrin rings Rise component : Depolarization time tdepolarization Figure 10. Transient absorption anisotropy decay profiles of CZ4, CZ6,and CZ8 in THF, The pump and probe wavelengths are 583 and 460 nm

23. Discussion The two different experimental observables ,S1-S1 annihilation and anisotropy depolarization, result in the similar EEH times between zinc(Ⅱ) porphyrin units. ・・・5 ・・・6 N: Number of hopping sites a:the angle between the adjacent trasition dipoles

24. Summary ・Excitation energy hopping rate increases with increase in molecular interaction because of short distance or small angle between porphyrin units.(Through space interaction) ・Excitation energy hopping rate increases arising from p-conjugation.(Through bond interaction)

25. Time-resolved fluorescence anisotropy Time-resolved fluorescence anisotropy ・・・2 I//(t)・・・parallel I┴(t)・・・perpendigular

26. Structures of the porphyrin rings