The Structure Effect of Squarylium Cyanine Dyes on Their Photophysical Characteristics

When a dye was introduced by different substituents at the same position of the dye,its photophysical properties can be changed. For the squaraine dyes, the effect of the substituents on the photophysical properties is expected to exhibit special regularity on account of the Donor-Acceptor-Donor nature of the dye. In this report, the absorption, emission spectrum, fluorescence quantum yield and fluorescence lifetime of the indolenium squaraines with the different substituents at C-5 of the indolenium moieties were studied, and those photophysical properties changed as the electron donating abilities of the substituents were observed. The absorption, emission maximum and the fluorescence lifetime changed as the Hammett substituent constant in folding linear.