Photoinduced Generation of Long-Lived Proton Transfer States: Photoinduced Proton Transfer from 2-(2‘,4‘-Dinitrobenzyl)pyridine to a Proton Cage, the [2.1.1] Cryptand

Abstract

Photoinduced proton transfer from 2-(2‘,4‘-dinitrobenzyl)pyridine (α-DNBP) to [2.1.1] cryptand (C211) is demonstrated and characterized by transient absorption spectroscopy. Proton transfer is shown to occur from two tautomers reached after optical excitation of α-DNBP. Protonation of C211 is expected to form a proton cryptate in which the proton is included in the intramolecular cavity and stabilized, so that the back-transfer reaction is considerably slowed. As a consequence, the α-DNBP anion, formed by deprotonation, survives on time scales that are at least 103 times longer than those observed in the presence of another proton acceptor of similar basicity, triethylamine, which was studied for comparison and which does not equally stabilize the proton. As deprotonation by C211 intercepts different tautomers of α-DNBP, information about the reaction pathways of photocoloration in this compound is gained.