Photochemical behaviour of N,N,N′,N′-tetramethylbenzidine and its protonated forms in sodium dodecyl sulphate anionic micelles under 337 nm laser irradiation

Abstract

Continuous 337 nm laser excitation of N,N,N′,N′-tetramethylbenzidine (TMB) in 0.1 mol dm^–3 sodium dodecyl sulphate micelles produces monophotonic ionization of the molecule. A study of the photoionization process has resulted in the following new results: (1) the radical-cation quantum yield decreases with adsorbed light because of its spectral overlap with TMB and its simultaneous photodestruction during irradiation, (2) partial regeneration of the TMB absorption band after radical-cation decay suggests that a principal mode of radical decay is through a disproportionation reaction, (3) the photoionization yield is affected by the degree of protonation of TMB, increasing with increasing bulk pH, and (4) diprotonated TMB, TMBH²⁺₂, photodecomposes into TMB²⁺.