DIPOLE-MOMENTS AND 2ND-ORDER HYPERPOLARIZABILITIES OF IMIDAZOLE-BASEDBETAINES DETERMINED FROM THE SOLVATOCHROMIC EFFECT

We report on results of measurements of the solvatochromic effect in t wo benzimidazole-based betaines (hereafter referred to as IB1 and IB2) . The solvatochromic shifts exceed 2000 cm(-1) in both molecules; howe ver, the directions of the shift were found opposite in spite of simil ar chemical structures of the molecules under study. The ground-state dipole moments in both betaines exceed 13 Debye units, whereas the exc ited-state moments, calculated from the solvatochromic shift, differ m arkedly amounting to ca. 3 D in IB1 and 18 D in IB2. Quantum-chemical calculations indicate that betaines enjoy some freedom of orientation of their fragments which may influence the energies and intensities of the electronic transitions. The second-order hyperpolarizabilities, e stimated from the measurements amount to ca. 20x10(-40) m(4)/V (4.8x10 (-30) esu) for IB1 and 55x10(-40) m(4)/V (13.8x10(-30) esu) for IB2.