Photobases are mild aromatic ground-state bases which upon electronic excitation are capable of picking up a proton from water ('spliting' water into OH- and the protonated photobase). The strongest photobases are capable of abstracting a proton from water within a few tens of ps. Picosecond fluorescence spectroscopy was used to study the photo-initiated proton-transfer reaction from water using the 5-methoxy quinoline photobase. The proton abstraction rate from water becomes faster in presence of cations in the order: Mg2+ &gt; Ca2+ &gt; Li+ &gt; Na+ &gt; K+. We also measure the effect of specific counter anions, the ClO4-, Cl- and I- anions and find this effect to counter the effect of the cations, being much smaller but not negligible to the effect of the cations. We discuss the molecular origins for the photobasicity phenomenon and the effect of different solvents on the increase basicity. In addition, we study binary mixtures of water with various aprotoic co-solvents and analyze the co-solvent effect on the proton abstraction rate from the aqueous fraction of the binary-solvent solution.

Proton abstraction from water by photobases

ACS Fall 2021

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