Abstract

Coupling between electronic excitation and proton transfer is relevant to the kinetics of redox reactions, in particular those involved in solar-to-fuel light harvesting. A prime example of such coupling occurs in photoacids, where electronic excitation leads to proton release in the excited state. Here, we systematically study the inverse of this effect, photobasicity, in which a molecule becomes more basic in the excited state compared to the ground state. This endows the molecule with light induced proton removal capability which is anticipated to be of use in driving reactions where proton transfer is kinetically challenging. To investigate the origins and tunability of photobasicity, a set of 5-R-quinoline derivatives (R = {NH2, CH3O, H, Br, Cl, CN}) were selected and their changes in pKa upon electronic excitation in aqueous solutions were determined. The Hammett parameters σp of these substituents, indicative of their electron withdrawing capability, span a range of −0.7 to +0.7. Using Forster cycl...

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