A series of mono- and dicationic monomethine cyanine dyes belonging to the thiazole orange family have been prepared via an improved synthetic procedure, by the condensation of benzothiazolium salts with quaternary salt of quinolines having reactive methyl group in the presence of triethylamine under solvent-free microwave irradiation. The effects of microwave power and irradiation time on yield were examined. The products were identified using elemental analysis, 1H-NMR, 13C-NMR, FTIR, FAB-MS, UV-vis spectra. The electronic absorption and steady state fluorescence spectra of prepared dyes have been investigated. Fluorescence properties indicate significance in singlet oxygen sensitization and makes the present compounds as potential candidates in the area of photodynamic therapy (PDT).