Bridging the Gap between the Gas Phase and Solution Phase: Solvent Specific Photochemistry in 4-tert-Butylcatechol

Eumelanin is a naturally synthesized ultraviolet light absorbing biomolecule, possessing both photoprotective and phototoxic properties. We infer insight into these properties of eumelanin using a bottom-up approach, by investigating an ultraviolet absorbing motif of eumelanin, 4-tert-butylcatechol. Utilizing a combination of femtosecond transient electronic absorption spectroscopy and time-resolved velocity map ion imaging, our results suggest an environmental-dependent relaxation pathway, following irradiation at 267 nm to populate the S1 (1ππ*) state. Gas-phase and nonpolar solution-phase measurements reveal that the S1 state decays primarily through coupling onto the S2 (1πσ*) state which is dissociative along the nonintramolecular hydrogen bonded “free” O–H bond. This process occurs in 4.9 ± 0.6 ps in the gas-phase and 18 ± 1 ps in the nonpolar cyclohexane solution. Comparative studies on the deuterated isotopologue of 4-tert-butylcatechol in both the gas- and solution-phase (cyclohexane) reveal kine...