Author(s): Samuel Archer
Mentor(s):
Institution SUU
Dipyrroles are a class of bicyclic and heterocyclic compounds ubiquitous in nature as subunits to biological photo-sensors. As such, these molecules have gained significant attention in the field of photochemistry due to their ability to undergo photooxidation. Because of these properties and the large absorptivity in the blue region of the electromagnetic spectrum, we are able to initiate these reactions upon irradiation of blue laser light. In this study, the photochemical behavior of a model dipyrrole representative of the central pyrrole pair in natural tetrapyrrole sensors was investigated to model and quantify the mechanism and conditions of its photoreactivity. When UV-vis spectroscopy readings were taken of the dipyrrole compound to observe the progress of the reaction over hours, transformation of the visible light absorbing feature decayed into a near-UV feature representative of a change of conjugation. Further, this transformation was found to be pH dependent and therefore protonation state dependent. We can calculate this process through series of computational calculations to determine ground state energies and structures, frontier molecular orbitals, and simulated UV-vis spectra for comparison to experimental data. We have found that while the primary excited state pathway is rapid decay back to the ground state, however, photooxidative solvent addition is still a viable pathway that significantly alters the pigment structure and light-harvesting function.