Donor–π-acceptor benzothiazole-derived dyes with an extended heteroaryl-containing conjugated system: synthesis, DFT study and antimicrobial activity

A series of novel derivatives containing an electron-donating N,N-dimethylaminophenyl ring connected to an electron-withdrawing benzothiazole or benzothiazolium moiety via a heteroaryl system (furan, thiophene or N-methylpyrrole) and up to two ethenylene groups have been synthesized and characterized. Furthermore, their nonlinear optical (NLO) properties have been investigated at the theoretical level using DFT and time-dependent DFT methods, and their antimicrobial activities were evaluated against a standard set of unicellular organisms. Both benzothiazole and benzothiazolium systems are predicted to exhibit large NLO responses, based on the calculated static molecular quadratic hyperpolarizabilities β0 as well as intramolecular charge transfer (ICT) transition characteristics. Moreover, the 3-alkyl-benzothiazolium salts were found to display high toxicity against several tested microbes.