Abstract: Fifteen new butadienyl chain substituted asycyanine colorants containing benzothiazole ring have been synthesized by catalytic condensation of various substituted 2-methy-3-isopropyl benzothiazolium iodide with 4-dimethylaminostyrylphenyl ketone, 4-dimethylaminostyryl-4’-methylphenyl ketone and 4-dimethylaminostyryl-4’-bromophenyl ketone in ethanolic DMF medium using piperidine as basic catalyst. These colorants were synthesized with the object to study the effect of electron acceptor (-Br group) and donor (-CH₃ group) substituent at the 4’-position in the chain β-phenyl nucleus on visible absorption maxima and to evaluate their bactericidal activity. The colorants were found to exhibit uniform increase of absorption maxima i.e. red shift (RS) when collated with analogues having no substituents in the β-phenyl nucleus and the analogues having vinylene chain irrrespective of electron acceptor or donor groups. They show blue shifts (BS) when compared to quinaldino-asycyanine colorants. Purified samples were also investigated in vitro against gram positive (E. aureus) and gram negative (E.coli) microbes using disc diffusion technique and found to be mildly active against some of the pathogens.

Keywords: Asycyanine colorants, benzothiazole, benzothaizolium iodide, dimethylaminostyrylphenyl ketone, visible absorption maxima, bactericidal activity.