Solvatochromic Effect in a Benzimidazole-Based Betaine: Determination of the Dipole Moments and Second-Order Hyperpolarizability |
| L. Ziółek, K. Palewska, J. Lipiński, J. Sworakowski Institute of Physical and Theoretical Chemistry, Technical University of Wrocław, Wyb. Wyspiańskiego 27, 50-370 Wrocław, Poland S. Nes̆půrek Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 16206 Prague, Czech Republic S. Böhm Prague Institute of Chemical Technology, 16628 Prague 6, Czech Republic and E.C. Meister Laboratory of Physical Chemistry, Federal Technical University (ETH), 8092 Zurich, Switzerland |
| Received: March 6, 1995; revised version: May 16, 1995 |
| Dedicated to Professors Krzysztof Pigoń, Józef W. Rohleder and Zdzisław Ruziewicz on the occasion of their 70th birthday. |
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| Results of measurements of the solvent-dependent shift of the low-energy absorption band solvatochromic effect in a benzimidazole-based betaine are reported in the paper. Measurements of absorption spectra in several solvents of different polarities were performed. The solvatochromic shift of the low-lying absorption band was found to exceed 3000 cm-1; the results obtained were then employed to calculate the ground- and excited-state dipole moment of the molecule. The spectroscopic measurements were supplemented by measurements of the ground-state dipole moment. A remarkable change in the charge distribution was found to occur upon the 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 × 10-40 m4/V (4.8 × 10-30 esu), depending on the solvent used. |
| DOI: 10.12693/APhysPolA.88.283 PACS numbers: 33.20.-t, 42.65.An, 42.70.Jk, 78.40.-q |