The solvent effect can be determined by solvent polarity scale or solvatochromic parameters.1 Solvent polarity is a commonly used term related to the capacity of a media for solvating neutral, charged, polar and apolar species. hydrogen- bonding) solute-solvent interactions. The solvent-dependent spectral shifts can arise from either nonspecific (dielectric enrichment) or specific (e.g. In this context, “first excited state means the so-called Franck-Condon excited state with the solvation pattern present in the ground state. Similarly the negative solvatochromism is due to better stabilization of the molecule in the ground-state relative to that in the excited state, with increasing solvent polarity. The positive solvatochromism is due to the increase in stability of the excited state with increasing solvent polarity. Solvatochromism is caused by differential solvation of the ground and first excited state of the chromophore. The electronic transitions of particular interest in this respect are π→π* and n→π* as well as charge transfer absorptions. The solvent effect on spectra, resulting from electronic transitions, is primarily dependent on the chromophore and the nature of the (σ→σ*, n→σ*, π→π*, n→π* and charge-transfer absorption) transition.
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