Electronic properties of 1-methyl-4-phenyl-1H-tetrazole-5(4H)-thiones: An experimental and theoretical study

The syntheses of 1-(4-methoxyphenyl)-4-methyl-1H-tetrazol-5(4H)-thione 1a, 1-methyl-4-phenyl-1H-tetrazole-5(4H)-thione 1b, 1-(4-chlorophenyl)-4-methyl-1H-tetrazol-5(4H)-thione 1c, 1-methyl-4-(4-nitrophenyl)-1H-tetrazol-5(4H)-thione 1d were carried out and their electronic absorption spectra were obtained in cyclohexane, THF, and acetonitrile. The UV spectra of 1a–d showed a modest dependence on the polarity of the solvent. The change of substituent on the tetrazolethione ring from a strongly electron donating group (p-C6H4OMe, 1a), to a moderately electron donating (C6H5, 1b) to a weakly electron withdrawing group (p-C6H4Cl, 1c) also produced minimal effect on the electronic properties of 1a–c. However, the presence of a strongly electron withdrawing group (p-C6H4NO2, 1d) on the heterocyclic ring produced a marked change in the UV spectrum. Time-dependent density functional calculations revealed that all the bands result from π → π* excitations with some degree of intramolecular charge transfer (ICT) within the molecules. Our studies further showed that as the acceptor strength is increased in the order: 1a (p-C6H4OMe) < 1b (C6H5) < 1c (p-C6H4Cl) < 1d (p-C6H4NO2), the ICT also increases. In accordance with the experimental observations, the calculated transitions also showed modest dependence on the polarity of the solvent.