Mechanism of the Laser Flash Photolysis of Rydimeric e-Tautomers of 4- N , N -Diethylaminoazobenzene in a 2-Propanol Medium

Difference transit absorption spectra (TASes) obtained via flash photolysis of isopropanol solutions of 4- N , N -diethylaminoazobenzene (DEAB) using 15 ns laser pulses at wavelengths of λ ex = 265 and 353 nm are analyzed. The inconsistency of constructing the mechanism of trans ( t ) → cis ( c ) photisomerization of DEAB based on the concept of this dye having a monomeric structure is shown. Based on the rydimeric concept of aminoazobenzene dyes, which include Rydberg dimers DEAB 2 , an adequate explanation is given of the nature of TAS signals with structures that change dramatically when in wavelength λ ex is altered. TAS signals of DEAB 2 are compared to ultrahigh-speed (subpico- and pico-second) TAS signals of rydimers of a reference aminoazobenzene (AAB 2 ) dye. It is established that the main difference between the structures of DEAB 2 TAS signals generated by pulses with indicated wavelengths λ ex is due to the excitation of various rydimeric e-tautomers. In addition, a rydimeric e-tautomer that is unstable in the ground state acquires increased stability in propanol and, by absorbing radiation with λ ex = 353 nm, alters the structure of one of its monomers to quinoid while remaining a rydimer. It is shown that when excited with radiation pulses at λ ex = 265 nm, a rydimeric e-tautomer (which is more stable in the ground state) dissociates into individual monomers, one of which isomerizes to form cis -DEAB molecules.