SOLVATOCHROMIC EFFECT IN A BENZIMIDAZOLE-BASED BETAINE - DETERMINATION OF THE DIPOLE-MOMENTS AND 2ND-ORDER HYPERPOLARIZABILITY

Results of measurements of the solvent-dependent shift of the low-ener gy absorption band solvatochromic effect in a benzimidazole-based beta ine are reported in tile paper. Measurements of absorption spectra in several solvents of different polarities were performed. The solvatoch romic shift of the low-lying absorption band was found to exceed 3000 cm(-1); the results obtained were then employed to calculate the groun d- and excited-state dipole moment of the molecule. The spectroscopic measurements were supplemented by measurements of the ground-state dip ole moment. A remarkable change in the charge distribution was found t o occur upon tile electronic excitation: both the experimental results and the calculations indicate that the ground-state dipole moment is close to 13 D, whereas in the excited state it amounts to ca. 3 D. The second-order hyperpolarizability of the molecule was calculated from the measurements; its off-resonance value amounts to ca. 20 x 10(-40) m(4)/V (4.8 x 10(-30) esu), depending on the solvent used. PACS number s: 33.20.-t, 42.65.An, 42.70.Jk, 78.40.-q