UV-vis absorption and fluorescence spectra, solvatochromism, and application to pH sensors of novel xanthene dyes having thienyl and thieno[3,2-b]thienyl rings as auxochrome
Masaki Matsui, Takaya Yamamoto, Kenta Kakitani, Siddanagouda Biradar, Yasuhiro Kubota, Kazumasa Funabiki
Dyes and Pigments
Novel xanthene dyes having thienyl and thieno[3,2-b]thienyl rings as auxochrome have been synthesized. The UV-vis absorption maximum in dichloromethane was in the order of the auxochrome: NEt2 (Rhodamine B, 558 nm) < 2-thienyl (569 nm) < 5-thieno[3,2-b]thienyl (608 nm). These new xanthene dyes colored only in non-hydrogen-bond accepting solvents such as chloroform and dichloromethane. The lactone precursors of the thienyl and thieno[3,2-b]thienyl derivatives colored by adding strong acids whose pKa value is lower than ‒2.2 and 0.23, respectively, whereas that of rhodamine B colored by adding weak acids whose pKa value is lower than 4.7. These results originate from less stability of colored cationic dyes by the heteroaromatics than by the diethylamino auxochrome.
Fluorescence, Sensors, Materials