Control of protonated Schiff base excited state decay within visual protein mimics: a unified model for retinal chromophores.

Abstract

Artificial biomimetic chromophore-protein complexes inspired by natural visual pigments can feature color tunability across the full visible spectrum. However, control of excited state dynamics of the retinal chromophore, which is of paramount importance for technological applications, is lacking due to its complex and subtle photophysics/photochemistry. Here, we combine ultrafast transient absorption spectroscopy and quantum mechanics/molecular mechanics simulations for the study of highly-tunable rhodopsin mimics, as compared to retinal chromophores in solution. We identify conical intersections and transient fluorescent intermediates with atomistic resolution, providing unambiguous assignment of their ultrafast excited state absorption features. Our results point out that the electrostatic environment of the chromophore, modified by protein point mutations, affects its excited state properties allowing control of its photophysics with same power of chemical modifications of the chromophore. The complex nature of such fine control is a fundamental knowledge for the design of bio-mimetic opto-electronic and photonic devices.