FR0-SB, a Schiff base chromophore, is capable of reversible proton abstraction from linear alcohols upon photoexcitation. A pKa change of 14 units in first electronic excited state (S1), derived from steady-state spectra using the Förster equation, yields a pKa of ~21 in S1. The photoinduced proton abstraction is driven by the change in the electronic structure of the system in the S1 in comparison to the ground state, depicted by a 4.5 times increase of the dipole moment value in S1. The excited state proton transfer (ESPT) propagates through an intermediate complex which comprises of a vibrationally relaxed FR0-SB in S1 sharing a proton with an alcohol molecule (FR0-SB . . . H—OR). Computational studies of the ESPT reaction coordinate, where the intermediate complex is the reactant while the protonated photobase (FR0-HSB+) along with the alkoxide (−OR) are the products, reveal the need for at least 3 alcohol molecules to complete the reaction. The two additional alcohol molecules are essential to the stabilization of the intermediate complex as well as the product ion-pairs. The ESPT in secondary alcohols is significantly diminished, which emphasizes the importance of the proximity of the alcohol hydroxy- proton to the imine nitrogen of the photobase. The presentation will highlight our efforts towards understanding the different aspects of the proton transfer dynamics following one- and two-photon excitation of the novel fluorene-based “super” photobase molecule FR0-SB.

Proton abstraction mechanism of the “super” photobase FR0-SB

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.