Synthesis and spectral characteristics of some highly soluble squarylium cyanine dyes

The synthesis of eight novel squarylium cyanine dyes is described. The dyes exhibit high solubility in organic solvents due to the introduction of the 1-sulfonatopropyl group onto the N-atom of the indolenine moiety. The condensation of the indolenine with squaric acid preceded smoothly, the reaction being catalyzed by a weak base. Spectral parameters of the dyes were correlated with the nature of the 5-substituent in the indolenium moeity. All the substituents studied in this work gave a bathochromic effect on absorption and emission, as well as enhancing the fluorescence quantum yield. The effects increased with the electron-donating ability of the substituent, due to involvement of the donor moiety in S-0-->S-1 excition and stabilization of the excited state. (C) 1997 Elsevier Science Ltd.