Halogen-substituent effect on the spectroscopic properties of 2-phenyl-6-dimethylaminobenzothiazoles. Issue 26 (27th June 2019) - Misawa, Rena
Graphical abstract: Highlights: 7-Halogenated derivatives of 6-dimethylamino-2-phenylbenzothiazoles were prepared. The halogenated derivatives have the deformed dimethylamino group by steric repulsion. The halogenated derivatives showed blue-shifted electronic absorption and fluorescence. Intersystem crossing from the fluorescence state suffers from heavy atom effect. Abstract: 6-Dimethylamino-2-phenylbenzothiazole (1 -H) is a push-pull benzothiazole fluorophore mimicking the firefly oxyluciferin structure. We newly prepared 7-chloro and 7-bromo derivatives of1 -H and its 4-acetyl derivative (2 -H), and their spectroscopic and photophysical properties were investigated. The halogenated derivatives showed the blue-shifted electronic absorption maxima and fluorescence emission maxima compared to1 -H and2 -H, resulted from the deformations of the NMe2 groups and the electron withdrawing properties of the halogen groups. In addition, the halogen substitutions accelerate intersystem crossing by heavy atom effect, resulting in a decrease in fluorescence quantum yields. Interestingly, however, the halogenated derivatives of2 -H still showed moderate fluorescence quantum yields. The halogenation effect is one of the guides to design push-pull benzothiazole fluorophores for tuning fluorescence properties.