Photoinduced intramolecular charge shift reaction in ammonium N-(3,5-dinitrobenzoyl)-α-phenylglycinate adducts

Ammonium N-(3,5-dinitrobenzoyl)-α-phenylglycinate adducts were synthesized and characterized by using different protonated amines as counter-ion: NH4+, (CH3–CH2–)2NH2+, (CH3–CH2–CH2)NH3+, (CH3–CH2–CH2–CH2–)NH3+ and (CH3–CH2–)3NH+. A photochemical process was observed under ultraviolet (λexc, 254 nm) or solar irradiation, both in solid state and in solution: DMSO, acetone or acetonitrile. 3,5-Dinitrobenzene and carboxylate groups, separated by an N-benzylamide bridge, are present in these adducts, acting as electron acceptor and electron donor, respectively. Spectroscopic analyses (NMR, IR and UV–vis) suggest a photoinduced intramolecular electron transfer. A first-order photochemical kinetics was proposed in DMSO/(n-propylammonium N-(3,5-dinitrobenzoyl)-α-phenylglycinate) solution; such behavior was similar for all adducts studied, probably due to total salt dissociation in solution. In the solid state, however, electron transfer process efficiency is directly proportional to Lewis base (amine) strength of the adduct counter-ion. Decarboxylation is observed after the irradiation process, giving rise to a σ-adduct intermediate, and subsequent formation of benzaldehyde and 3,5-dinitrobenzamide degradation products.