Effect of UV-irradiation on spectral properties of squaraine dye in diluted solutions

• The effect of UV-irradiation on squaraine dye in diluted solutions of six solvents has been studied by absorption spectroscopy.
• The molecular interactions between solute-solvent have been explained by theoretical calculations.
• Dimethyl sulfoxide caused the most photostabilizing effect on dye due to specific interactions and complex formation.
• The fastest photolysis of dye has been observed in chloroform solution.

The photosensitive symmetric derivative of quadratic acid (DMSAQ) was been synthesized for the biomedical or analytical purposes. The photochemical properties of the obtained dye were studied by means of absorption spectroscopy in six solvents of different polarity and photoreactivity: chloroform (CHCl3), tetrahydrofuran (THF), ethanol (EtOH), acetonitrile (ACN) dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). Both high-energy radiation (UV–vis) and radiation with lower energy from visible range were applied. It was found that the fastest squaraine dye bleaching takes place in CHCl3 and DMF solutions, which is caused by photosensitivity of these solvents. The most spectacular stabilization effect has been found in DMSO under both visible and ultraviolet radiation. It was shown that the course of photochemical reactions of squaraine in solutions depends on the solvent properties, energy of radiation and mutual solute-solvent interactions. The explanation of squaraine structure and molecular interactions and their impact on photochemistry of studied systems has been supported by theoretical calculations.