Where λmax is the wavelength of the maximum of the longest wavelength of π→π* absorption band of betaine dye.10 The parameters are simply defined, in analogy to Kosower's Zvalues,8 as the molar electronic transition energies (ET) measured in kilocalories per mole (kcal/mol) at room temperature (25 ℃) and normal pressure (1 bar),9 and can be determined by Eq. ET(30) values are based on the negatively solvatochromic pyridinium N-phenolate betaine dye as the probe molecule. Spectroscopic solvent polarity parameters have been derived from solvent-sensitive standard compounds absorbing radiation in spectral ranges corresponding to UV/Visible, IR, ESR, and NMR spectra.3-7Īmong the single-parameter approaches, the ET(30) scale as one of the more comprehensive solvent scales. Attempts to express it quantitatively have mainly involved solvent properties such as relative permittivity, dipole moment, or refractive index, but these parameters cannot effectively account for the multitude and specific interactions of solute-solvent on the molecular-microscopic level2. 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.

Polarity parameter for diethyl ether