Studies on solvatochromic behavior of dyes using spectral techniques

• The paper compiles recent studies on solvatochromism, with particular emphasis on azo dye solutions.
• It provides a brief account of solvent–dye interactions and their effect on spectral behavior.
• Factors affecting solvatochromism are discussed. Some of these are inherent to the dye molecule.
• Solvatochromism is also effected by the type of tautomeric structures and substituents.
• Correlation of solvent parameters and use of mathematical models is also highlighted.

This paper is a compilation of recent studies on solvatochromism, with particular emphasis on azo dye solutions. It provides a brief account of solvent–dye interactions and their effect on the spectral behavior. The factors that affect solvatochromism are discussed. Some of these factors are inherent to the dye molecule, such as equilibria of tautomer/resonance structures and substituent effects. Others are associated to the solvent properties like solvent polarity, stabilization of charges in the solvation sphere and solvent interactions with the dye in the ground and excited state. The effect of temperature on the solvent–dye interactions is also examined. Another important aspect of solvatochromic studies, namely the fitting of spectroscopic values to solvent parameters and the use of mathematical models to correlate with polarity scales, is also highlighted.