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T he term solvatochromism is used to descr ibe the pronounced change in position and sometimes intensity of a UVvisible absorption band following a change in the polarity of the medium. When absorption spectra are measured in solvents of different polarity it is found that not only the position but also the intensity and shape of the absorption band can vary, depending on the nature of the solvent. The in uence of solvents on the course of chemical reactions has been studied for a long time, and efforts have been made to correlate equilibrium constants, reaction rate constants, or positions of ultraviolet absorption bands with the so-called ‘‘polarity’’ of the solvent.1 Attempts made to express the polarity in terms of dielectric constant, dipole moment, or other properties of the solvent have not been very successful, largely due to the simpli cations used. 2 The polarity of a solvent is determined by its sol-
Nigam et al. (Thu,) studied this question.