Luminescence spectral properties of new benzothiazole polymethine dye

Abstract

The absorption and fl uorescence spectra of a new styryl derivative of thiofl avin T 2-{(1E,3E)-4-[4-(dimethylamino)-2,6-dimethylphenyl]buta-1,3-dien-1-yl}-3-ethyl-1,3-benzothiazol-3-ium tosylate (Th-C23) in solvents with diff erent polarity and viscosity and also incorporated in the structure of amyloid fi brils and bovine serum albumin were investigated. A characteristic feature of the dye is an extremely low quantum yield of fl uorescence in low-viscosity solvents (10–4 in water) which, however, increases signifi cantly in viscous solutions and when it is incorporated in the structure of proteins or amyloid fi brils. In the latter case the quantum yield increases by 8∙10 times. On the basis of the experimental studies and quantum chemical calculations it was shown that Th-C23 exhibits the properties of a molecular rotor. The increase of the fl uorescence quantum yield in viscous solutions and in the biopolymers results from limitation of the torsional rotation of the molecular fragments, leading to fl uorescence quenching. The long-wavelength location of the absorption spectrum and the fl uorescence spectrum of the new dye in the red region of the spectrum (520 and 600 nm) makes it possible to use it as a fl uorescent marker that is sensitive to the viscosity (hardness) of the microenvironment not only in vitro but also in vivo.