2. Contents:  Introduction.  Natural Photosynthesis.  Antenna Effect.  Chromophores used in Artificial photosynthetic arrays:  Porphyrins  Dendrimers  Fullerenes  Rylenes  Conclusion.

3. Introduction 165,000 TW of sunlight hit the earth every day 165,000 TW of sunlight strike the earth every day.

4. bluegreenorangered Electromagnetic spectrum

5. NATURAL PHOTOSYNTHESIS

6. Schematic representation of bacterial light harvesting complexes. N.W.Isaacs et al, Nature, 1995, 374, 517

8. Antennae Light Excitation transfer Pigment molecules Electron transfer e - acceptor e - donor Antenna Effect

9. Requisites for light harvesting:  Absorption of visible light.  Stability to photolysis.  Efficient energy transfer process.  High energy content.  Long lived excited state.  Appropriate kinetic factors.

10. Pen RC Pen C C CC hh hh hh hh h’h’ EE EE EE EE Pen : Energy transfer photosensitiser. RC : Reaction Centre C : Connectors Intramolecular Light Harvesting systems : Testing the efficiency of energy transport

11. e¯e¯ e¯e¯ hh hh hh hh hh hh hh ReI PeI Pen R’eI Fujihira et al, Thin Solid Films, 1989, 180, 43 Pen Rel PelR’el Light harvesting on monomolecular layer assembly Pel : Electron transfer photosensitiser Pen: Energy transfer photosensitiser Rel: Electron relay

12. Meyer.T.J.et al,J. Am. Chem. Soc. 1989, I l l, 9101 Remote Photosensitisation

13. Synthetic multiporphyrin arrays have been frequently prepared to shed light on light harvesting processes. Porphyrins are more stable and accessible synthetically than chlorophylls. Absorption properties: strongly in the blue and weakly or moderately in the green regions. Porphyrins:

14. Dyad Q P Yanagita.M., et al, Tetrahedron Lett, 1979, 20, 257 1 2 3

15. C-P-Q Triad Moore.T.A., et al., Nature, 1984, 307, 630 C C-P-Q C- 1 P-Q C-P  + -Q  - C  + -P-Q  - 0.0 1.0 2.0 Energy (eV) 1 2 3 5 4 P Q t= 2µs (in butyronitrile) t= 300ns (in CH 2 Cl 2 )

16. Gust, D., et al, J. Am. Chem. Soc. 1997, 119, 1400. C P C 60 Triad C-P-C 60 C- 1 P-C 60 C-P- 1 C 60 C-P  + -C 60  – 1 [C  + -P-C 60  – ] 3 [C  + -P-C 60  – ] 3 [C-P-C 60 ] 1 2 3 4 567 8 109 11 E (eV)  = 4.9µs (in MTHF)

17. Sauvage.J.P., et al, Chem. Soc.Rev., 2004, 33, 147 Triad  = 75 ns (in CH 3 CN)

18. ++ –– ++ –– Tetrad Gust.D.,Moore.T.A., et al, Science, 1989, 244, 35  = 460ns

19. Fukuzumi.S, Guldi,D.M et al, J.Am.Chem.Soc. 2001, 123, 6617 Tetrad ++ ––  = 0.38s

20. Pentad Gust.D,Moore.T.A et al, Science, 1990, 248, 199 –– ++ CP Zn PHPH QNQN QBQB  = 55 µs

21. CP Zn PHPH QNQN QBQB –– ++ Gust.D,Moore.T.A et al, Science, 1990, 248, 199

22. Hexad Gust. D., Lindsey.J, et al, J.Am.Chem.Soc. 1999, 121, 8604 energy transfer 50 ps energy transfer 244 ps charge separation 3 ps charge recombination 1330 ps

23. Lindsey, J., et al, J. Org. Chem. 1999, 64, 9101. Increasing the spectral coverage absem

24. Lindsey et al J. Mater. Chem., 2002, 12, 65.

25. Lindsey, J. et al Org. Lett., 2000, 2, 17 Self Assembly of Light Harvester / Reactive Chromophore Assemblies

26. They are nanoscale macromolecules which are highly branched polymers with precisely controlled architectures. Dendrimers:

27. Balzani V, Lehn J-M, et al, Angewandte Chemie, 1987, 26, 1266

28. Moore et al, Angewandte Chemie, 1993, 32, 246

29. Armaroli N. et al, Chem.Eur.J, 2003, 9, 37

30. Potential uses and positioning of metals within dendritic architectures Newkome.G.R., et al,Chemical Reviews, 1999, 99, 1689

31. Aida.T. et al, Chem.Eur.J. 2002, 8, 2667 Zn-P H 2 -P h’h’ h h 

32. Metal complexes: Absorption of light from MLCT transitions. MLCT states has many desirable features: 1)Photochemical stability. 2)Stable one electron oxidised and reduced forms. 3)Sufficiently long lifetime.

33. Balzani.V., et al, Coord Chemistry Reviews, 2001, 219–221, 545 Dendrimers with metal complexes in each branching centre.

34. Light harvesting and antenna effect Balzani.V., et al, Coord.Chem.Reviews, 2001, 219–221, 545.  - Os 2+  - Ru 2+

35. Balzani.V., et.al, New. J. Chem., 1999, 23, 63 Dendrimer having a metal complex as the core

36. RYLENES Wasielewski.M.,et al, J.Am.Chem.Soc, 2004, 126, 12268

37. Conclusion: Artificial photosynthetic arrays by the incorporation of various chromophores have been looked into. These arrays mimic certain aspects of natural photosynthetic systems. According to Giacomo Ciamician: “The photochemical processes, that hitherto have been the guarded secret of the plants, will have been mastered by human industry which will know how to make them bear even more abundant fruit than nature, for nature is not in a hurry but mankind is.”

38. Acknowledgements Dr. Russell H. Schmehl Dr. Mark J. Fink Dr. James P. Donahue Group Members: Dr. Kumaresan Duraisamy Heidi Hester Srivathsa Vaidya Rupesh Narayana Prabhu David Karam Chemistry Department, Tulane University