Non-Uniform Excited State Electronic-Vibrational Coupling of Pigment–Protein Complexes

• DOI: 10.1021/acs.jpclett.0c02454
• Publication Date: 2020-11-25T22:34:00Z
• Authors: Shawn Irgen-Gioro; Karthik Gururangan; Austin P. Spencer; Elad Harel
• Keywords: Vibronic coupling; Chromophore; Vibronic spectroscopy; Vibrational energy relaxation

Photosynthetic organisms exploit interacting quantum degrees of freedom, namely intrapigment electron-vibrational (vibronic) and interpigment dipolar couplings (J-coupling), to rapidly efficiently convert light into chemical energy. These interactions result in wave function configurations that delocalize excitation between pigments pigment vibrations. Our study uses multidimensional spectroscopy compare two model photosynthetic proteins, the Fenna–Matthews Olson (FMO) complex harvesting 2 (LH2), confirm long-lived excited state coherences originate from vibrational modes pigment. Within this framework, J-coupling vibronic should have a cascading effect modifying structured spectral density excitonic states. We show FMO effectively couples all its excitations uniform set vibrations while LH2, chromophore rings each couple unique environment. simulate energy transfer simple system with non-uniform coupling demonstrate how modification strength can modulate transfer. Because increasing increases internal relaxation, strongly coupled states act as an funnel, which potentially benefit transport.