Photochemical reaction dynamics take place on potential energy surfaces of electronically excited states that are often well separated from one another in energy.  However, when the chromophores are identical, small differences in local environment lead to closely spaced potential energy surfaces with intriguing consequences for vibronic coupling.  In this talk, I will describe our recent studies of the single-conformation spectroscopy of 1,2-diphenoxyethane (DPOE) and its complex with a single water molecule.  In the DPOE monomer, the two observed conformers both have S1 and S2 states that are split by only 1.0 cm-1.  The water molecule binds to DPOE asymmetrically, forming a bridge between the phenoxy O and aromatic p clouds of the two chromophores.  The asymmetric binding geometry localizes the two electronically excited states, producing a site splitting between S1 and S2 states of 190 cm-1.  This talk will discuss the way in which the OH stretch infrared spectrum of the H2O molecule reports on the electronic excitation, its localization on one or the other rings, and the mixed electronic character of the (nominal) S2 state.  The water molecule bridge thus plays a dual function, localizing the electronic excitation in the bichromophore and directing electronic energy transfer between the two chromophores.

Solvent effects on vibronic coupling in a flexible bichromophore: Electronic localization and energy transfer induced by a single water molecule

245th National Meeting (2013)

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