Photochemical Reactions of Aminoazobenzene in Solutions, According to Ultrafast Vis Spectroscopy Data

Abstract

Photoinduced processes (photonics) in trans-aminoazobenzene (t-AAB) are determined by analyzing literature data on transient Vis spectra upon pulsed laser excitation at λ_ex = 400 nm. The analysis is based on the concepts of the rydimer structure of aminoazobenzene dyes, particularly t-AAB₂ (the ground state of the dye). It is shown that the photochemical emergence and subsequent transformation of the transient spectra, along with the isomerization of t-AAB₂ to cis-aminoazobenzene (c-AAB), are caused by simultaneous events of the splitting of t-AAB₂ rydimers into monomers; the splitting of the rydimers is induced by the absorption of visible light by cations of the phenylaminyl type (chromogens of t-AAB₂ rydimers). The mechanism of the process is described, which includes the formation of two types of Franck–Condon monomer pairs of t-AAB. As is shown, a pair of one type consists of two identical monomers; it relaxes into the initial t-AAB₂ rydimer. A pair of the other type contains one monomer t-AAB and a doubly charged monomer with two cations of the phenylaminyl type and the absorption of visible light in the 500–750 nm range of wavelengths; the monomer dication isomerizes into c-AAB. Structural formulas of the transient electronic configurations are given that explain the photonics of t-AAB₂ rydimers.