Dihydroquinolylazotetrazole dyes: Effect of a substituent at the tetrazole fragment on spectral properties and thermal ‒ isomerization in organic solvents

New hetarylazo dyes with dihydroquinoline and tetrazole moieties with different substituents at the tetrazole cycle were synthesized and their spectral properties and thermal Z‒E isomerization were investigated in toluene, MeCN and DMSO. The substitution of H with the CH 3 group at the tetrazole fragment results in the disappearance of concentration dependence of the absorption spectra observed for the dyes with unsubstituted tetrazole in MeCN and DMSO. The time-resolved measurements in MeCN and DMSO show the existence of several forms of Z- isomers with lifetimes on μs‒ms time scale for the dyes with unsubstituted tetrazole and a single Z- isomer for the dyes with the CH 3 group at tetrazole. The position of the CH 3 group at the tetrazole fragment affects the lifetime of the Z- isomer, which changes from ms to seconds and minutes on passing from 2-methyl- to 1-methyl-tetrazole. The structural features of the dihydroquinolylazotetrazole dyes and complex formation with solvents are discussed. • Methyl group at the tetrazole fragment changes spectral properties of the dihydroquinolylazotetrazole dyes. • Position of the methyl group at the tetrazole fragment determines the lifetimes of the Z -isomers. • Complexation with amphiphilic solvents determines the concentration dependence of the spectra with unsubstituted tetrazole.