Synthesis, spectroscopic characterization and photophysical study of dicyanomethylene-substituted squaraine dyes

In this work, the synthesis and the photophysical study of novel symmetrical and unsymmetrical squaraine dyes is described. These dyes were prepared by base-catalyzed condensation reaction between 3H-indolium or benzothiazolium salts with dicyanomethylene squarate, derived from squaric acid. The photophysical behavior of the dyes was investigated using UV–Vis absorption and steady-state fluorescence in solution. Additionally, its association with albumin from bovine serum (bovine serum albumin [BSA]) was also investigated. The dyes present strong absorption in the red/infrared regions and fluorescence emission in the infrared region tailored by the electronic structure of the squaraine. Association experiments with bovine serum albumin indicate that the obtained squaraine dyes are suitable for protein detection in solution.