Solvatochromism of heteroaromatic compounds: XXVIII. Factors affecting the nonspecific solvatochromic effect in the UV spectra of aromatic nitro compounds in aprotic protophilic solvents

Examination of the UV spectra of a large series of solvatochromic indicators of the general formula 1-X-4-NO₂-C₆H₄ in aprotic solvents confirmed the proportionality between the dipole moments of these compounds in the ground (μ_g) and first electronically excited (¹ A ₁, μ_e) states: μ_e = r _μμ_g. The coefficient r _μ was determined by applying the equation of the Bakhshiev-Bilot-Kawski solvatochromism theory both to nonspecifically solvated molecules and to their H complexes with aprotic protophilic solvents. An anisotropy of the electron redistribution was revealed for low-symmetry 1-substituted 2,4-dinitrobenzenes. The r _μ value obtained allowed the calculation of the Kamlet-Taft empirical solvatochromic parameter π* on the basis of generalized characteristics of the solvent.