Contents: Introduction. Natural Photosynthesis. Antenna Effect. Chromophores used in Artificial...
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Transcript of Contents: Introduction. Natural Photosynthesis. Antenna Effect. Chromophores used in Artificial...
Contents:
Introduction.
Natural Photosynthesis.
Antenna Effect.
Chromophores used in Artificial photosynthetic arrays:
Porphyrins
Dendrimers
Fullerenes
Rylenes
Conclusion.
Introduction
165,000 TWof sunlighthit the earthevery day
165,000 TW of sunlightstrike the earth every day.
blue green orange red
Electromagnetic spectrum
NATURAL PHOTOSYNTHESIS
Schematic representation of bacterial light harvesting complexes.
N.W.Isaacs et al, Nature, 1995, 374, 517
Antennae
Light Excitation transfer
Pigment molecules
Electron transfer
e - acceptor
e- donor
Antenna Effect
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.
Pen
RC
Pen
PenPen
C C
C C
h
h h
hh’
E E
EE
Pen : Energy transfer photosensitiser.
RC : Reaction Centre
C : Connectors
Intramolecular Light Harvesting systems : Testing the efficiency of energy transport
e¯
e¯h h h h h h h
ReI
PeI Pen Pen PenPen Pen Pen
R’eI
Fujihira et al, Thin Solid Films, 1989, 180, 43
Pen
Rel Pel R’el
Light harvesting on monomolecular layer assembly
Pel : Electron transfer photosensitiser
Pen: Energy transfer photosensitiser
Rel: Electron relay
Meyer.T.J.et al ,J. Am. Chem. Soc. 1989, I l l , 9101
Remote Photosensitisation
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:
Dyad
Q
P
Yanagita.M., et al, Tetrahedron Lett, 1979, 20, 257
1
2
3
C-P-Q Triad
Moore.T.A., et al., Nature, 1984, 307, 630
C
C-P-Q
C-1P-Q
C-P+-Q-
C+-P-Q-
0.0
1.0
2.0
Ene
rgy
(eV
)
1
2
3
5
4
PQ
= 2µs (in butyronitrile)= 300ns (in CH2Cl2)
Gust, D., et al, J. Am. Chem. Soc. 1997, 119, 1400.
C P C60
Triad
C-P-C60
C-1P-C60
C-P-1C60
C-P+-C60–
1[C+-P-C60– ] 3[C+-P-C60
–]
3[C-P-C60]
1
2
3
4
5 6 7
8
109
11
E (eV)
= 4.9µs (in MTHF)
N
N
N
Ru N
N
N
N
NH N
HN N
N N
NAu
Sauvage.J.P., et al, Chem. Soc.Rev., 2004, 33, 147
Triad
= 75 ns (in CH3CN)
+–
+–
Tetrad
Gust.D.,Moore.T.A., et al, Science, 1989, 244, 35
= 460ns
Fukuzumi.S, Guldi,D.M et al, J.Am.Chem.Soc. 2001, 123,
6617
Tetrad
+ –
= 0.38s
Pentad
Gust.D,Moore.T.A et al, Science, 1990, 248, 199
–+
C PZn PH QN QB
= 55 µs
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 pscharge recombination 1330 ps
Lindsey, J., et al, J. Org. Chem. 1999, 64, 9101.
Increasing the spectral coverage
abs em
Lindsey, J. et al Org. Lett., 2000, 2, 17
Self Assembly of Light Harvester / Reactive Chromophore Assemblies
They are nanoscale macromolecules which are highly branched polymers with precisely controlled architectures.
Dendrimers:
Balzani V, Lehn J-M, et al, Angewandte Chemie, 1987, 26, 1266
Moore et al, Angewandte Chemie, 1993, 32, 246
Armaroli N. et al, Chem.Eur.J, 2003, 9, 37
Potential uses and positioning of metals within dendritic architectures
Newkome.G.R., et al,Chemical Reviews, 1999, 99, 1689
Aida.T. et al, Chem.Eur.J. 2002, 8, 2667
Zn-P
H2-P
h’
h
Balzani.V., et al, Coord Chemistry Reviews, 2001, 219–221, 545
Dendrimers with metal complexes in each branching centre.
Light harvesting and antenna effect
Balzani.V., et al, Coord.Chem.Reviews, 2001, 219–221, 545.
- Os2+
- Ru2+
Balzani.V., et.al, New. J. Chem., 1999, 23, 63
Dendrimer having a metal complex as the core
RYLENES
Wasielewski.M.,et al, J.Am.Chem.Soc, 2004, 126, 12268
Conclusion:Artificial photosynthetic arrays by theincorporation 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.”
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