In many biological systems such as the photosynthetic Fenna-Matthews-Olson complex, chromophores occur in clusters held together by a protein. Due to the electronic coupling mediated by the encapsulating protein, the electronic degrees of freedom couple with vibrational motion breaking down the Born-Oppenheimer approximation. Understanding these non-Born-Oppenheimer processes is crucial for replicating the efficiency of biological light-harvesting complexes.Since Witkowski and Moffitt's original proposal of modeling vibronic coupling in symmetric bichromophores, similar methodology has been used to simulate absorption and emission spectra in a variety of molecular dimers and aggregates. We have previously extended the vibronic model to asymmetric dimers and applied it to flexible bichromophores, diphenylmethane (DPM) and its deuterated analogue (d5-DPM). In this work we further extend the method to asymmetric multi-chromophore systems that have nearly degenerate electronic excited states. Our multi-chromophore vibronic coupling model also accounts for intermonomer vibrational modes that played an important role in modeling absorption and emission spectra in flexible multi-chromophores. In order to include several spectroscopically active inter- and intra-monomer vibrational modes in a simulation, an iterative matrix diagonalization is employed. The new multi-chromophore model is used to simulate the vibronic spectra in tricyclophane, a tri-chromophore. Parameters for the model are obtained from ab initio calculations while the resulting spectra are compared to high-resolution experimental spectra obtained by Zwier and co-workers [Zwier, private communication].

Vibronic coupling in asymmetric multichromophores: Application to tricyclophane

246th National Meeting (2013)

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