First hyperpolarizability in a new benzimidazole derivative

A new benzimidazole, 2-(4'-amino-2'-hydroxyphenyl)-6-nitrobenzimidazole (LEN), with promising applications in nonlinear optics were synthesized, purified and characterized by classical techniques. The UV-Vis and steady-state fluorescence of LEN in solution were applied in order to characterize the photophysical behaviour of this new fluorescent dye. The Hyper-Rayleigh Scattering study indicates a remarkable increase in the beta absolute value (1197.3 +/- 1.2 x 10(-30) esu) of the LEN in acetone at 1064 nm, when comparing with a previously described benzoxazole (BO6). The ratio between the experimental beta and the maximum theoretical value using a two-level model was also improved by a factor 6. Ab initio and semi-empirical calculations of the dipole moments and the first hyperpolarizability are also presented. The enhancement in the experimental hyperpolarizability value in relation to BO6 is explained in terms of the benzimidazolic ring basicity and a prototropic effect (annular tautomerism) present in the LEN, identified as a resonance-assisted hydrogen bond, which leads to a stronger electronic delocalization. (C) 2004 Elsevier B.V. All rights reserved.3054169911512