Semiempirical calculations indicate that the interplanar angle between the two aromatic rings leads to enhancement in the NLO properties of these compounds. The confirmation of this feature may be provided by the study of a new series of stericallyhindered pyridinium phenolates 2a–e bearing two tert-butyl substituents at the ortho position(s) of the phenolate functionality. Such bulky groups would enhance
confirms the π* dependence of the CSh band shift but also demonstrates a clear β dependence. The contribution of the latter parameter to the band hypsochromy is markedly increasing with ΘAD. Such an unusual effect was ascribed to a much higher ESPT rate relative to the highly twisted conformation with respect to that of more planar geometry. Despite the suppression of the geometrical relaxation in ethanol