Vibrational spectral investigation of four second order nonlinear optical azobenzene-containing materials: A combination of experimental and density functional theoretical (DFT) study

In this work, four-second order nonlinear optical (NLO) azobenzene-containing materials are studied in-depth by using vibrational spectra and density functional theory (OFT). The Fourier transform infrared (FT-IR) spectra and FT-Raman spectra are recorded in the range of 50-4000 and 100-3600 cm(-1), respectively. Meanwhile, the OFT computations are performed at B3LYP/6-31G (d,p) level to derive equilibrium geometry, vibrational wavenumbers and intensities, and first hyperpolarizability, and the scaled theoretical wavenumbers are also shown to be in good agreement with experimental data. The calculated results show that these four azobenzene-containing compounds are good materials and the compound with nitro substituent groups possesses a larger first molecular hyperpolarizability (beta) value. Moreover, the simultaneous infrared and Raman activation of R-1 group and C=C stretching suggest that the charge transfer interaction might occur between the R-1 group and phenyl ring, and the HOMO-LUMO gap analysis also supports this viewpoint. (C) 2011 Elsevier B.V. All rights reserved.