Session: Physical Chemistry Poster:

Multidimensional spectroscopies have found a wide use in uncovering the dynamical phenomena at play in the energy transfer in photosynthetic and other light-harvesting systems. Recently, two-dimensional electronic vibrational (2DEV) spectroscopic studies have shown that vibronic coupling plays a significant role in the energy transfer in such systems, however, the nature of the vibronic coupling mechanism remains unclear. To uncover the signatures of different mechanisms of vibronic coupling we have developed a phenomenological model of a multi-chromophoric system with which we have performed 2DEV calculations. In this model, two chromophores with local high-frequency nuclear coordinates are coupled through dipole-dipole interactions and a single low-frequency mode that is nearly resonant with the energy gap of the two electronic states is added to induce vibronic coupling. In this way, we can control the vibronic mixing through the Franck-Condon activity as well as the Herzberg-Teller activity to systematically study these signatures in 2DEV spectroscopy. The spectra show that the different vibronic coupling mechanisms arise in different features—Franck-Condon activity mainly shows up in the vibrational detection dimension and Herzberg-Teller coupling is found mainly along the electronic excitation dimension. It is found that the vibronic mixing is predominantly controlled by the Franck-Condon activity of the low-frequency mode and that the Herzberg-Teller activity changes the phase relationships of the characteristic frequencies associated with the energy transfer dynamics. These changes in the dynamical beating help resolve the differences between bare electronic coherences and vibronic coherences. The spectra are also compared to the population dynamics where it is shown that the vibronic mixing has a significant effect on the rate of energy transfer with the same signatures from the different vibronic coupling mechanisms. This model thus shows the signatures of vibronic coupling in 2DEV spectroscopy as well as in the population dynamics, which furthers the utility of this experimental technique in studying systems where electronic and nuclear coupling plays a large role.

David Limmer

Professor, University of California Berkeley

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