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Self-Assembly of Supramolecular Light-Harvesting Arrays from Covalent Multi-Chromophore Perylene-3,4:9,10-bis(dicarboximide) Building Blocks

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journal contribution
posted on 07.07.2004, 00:00 by Michael J. Ahrens, Louise E. Sinks, Boris Rybtchinski, Wenhao Liu, Brooks A. Jones, Jovan M. Giaimo, Alexy V. Gusev, Andrew J. Goshe, David M. Tiede, Michael R. Wasielewski
We report on two multi-chromophore building blocks that self-assemble in solution and on surfaces into supramolecular light-harvesting arrays. Each building block is based on perylene-3,4:9,10-bis(dicarboximide) (PDI) chromophores. In one building block, N-phenyl PDI chromophores are attached at their para positions to both nitrogens and the 3 and 6 carbons of pyromellitimide to form a cross-shaped molecule (PI-PDI4). In the second building block, N-phenyl PDI chromophores are attached at their para positions to both nitrogens and the 1 and 7 carbons of a fifth PDI to produce a saddle-shaped molecule (PDI5). These molecules self-assemble into partially ordered dimeric structures (PI-PDI4)2 and (PDI5)2 in toluene and 2-methyltetrahydrofuran solutions with the PDI molecules approximately parallel to one another primarily due to π−π interactions between adjacent PDI chromophores. On hydrophobic surfaces, PDI5 grows into rod-shaped nanostructures of average length 130 nm as revealed by atomic force microscopy. Photoexcitation of these supramolecular dimers in solution gives direct evidence of strong π−π interactions between the excited PDI chromophore and other PDI molecules nearby based on the observed formation of an excimer-like state in <130 fs with a lifetime of about 20 ns. Multiple photoexcitations of the supramolecular dimers lead to fast singlet−singlet annihilation of the excimer-like state, which occurs with exciton hopping times of about 5 ps, which are comparable to those observed in photosynthetic light-harvesting proteins from green plants.

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