1-(Carbamoylmethyl)-3H-indolium squaraine dyes: Synthesis, spectra, photo-stability and association with BSA

Novel, squarylium dyes containing 1-(alkylcarbamoylmethyl)-2,3,3-trimethyl- 3H-indolium groups were synthesized and their UV/Vis and fluorescence spectra, aggregation, photo-stability and association with bovine serum albumin were studied. The absorption and emission max wavelengths of the dyes in different solvents were in the range 619–653 nm. Compared to a typical ethyl squarylium dye, the introduction of alkylcarbamoylmethyl groups reduced aggregation and improved molar extinction coefficient, fluorescence quantum yield and photo-stability in water. Moreover, the fluorescence intensity of the dyes increased upon the addition of BSA in pH 7.0 phosphate buffer solution. An excellent linear relationship (r2 = 0.9982) was obtained between fluorescence intensity and bovine serum albumin concentration.