TCBG Seminar

Collective Electronic Excitations and Coherence Sizes in Dendrimers and Photosynthetic Antennae

Professor Shaul Mukamel
University of Rochester
Rochester, New York

Tuesday, October 16, 2001
3:00 pm (CT)
2269 Beckman Institute


A time dependent collective electronic oscillators (CEO) picture that connects the optical properties of large conjugated molecules directly with the motions of electron-hole pairs in real space is presented. The electronic oscillators are quasiparticles which represent the dynamics of the optically- driven reduced single electron density matrix. Considerable computational advantages and a clear physical insight into the origin of the optical response are provided by the underlying coherence-transfer pathway. Real space analysis of the transition electronic density matrices shows the charge and bond- order redistribution taking place upon photoexcitation and results in a systematic procedure for identifying the electronic coherence sizes which control the scaling and saturation of spectroscopic properties with molecular size and geometry. A microscopic algorithm for dissecting aggregates into effective independent chromophores is presented and applied to the chlorophylls and carotenoids in photosynthetic light-harvesting antenna complexes and to Phenylacetylene Dendrimers. The distribution of cooperative radiative decay rates is calculated. This distribution, which depends on both the exciton coherence sizes and aggregate geometry, can be directly observed using single-molecule spectroscopy. Optical properties femtosecond relaxation processes following and energy funneling in dedrimers are analyzed. Various coherent pulse sequences designed to probe energy transfer and relaxation pathways in aggregates will be discussed.

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