Optical poling of several halogen derivatives of pyrazoloquinoline

Paper deals with optical absorption and second-order optical poling effect in a new synthesized halogen derivatives of 1H-pyrazolo[3,4-b]quinoline. The experimental study and quantum chemical simulations are presented. In optical poling experiment (fundamental wavelength lambda = 1.76 mum) we have found that the maximal output of second-order susceptibility (up to 1.53 pm/V) is observed for the chromophore possessing two methyl groups and fluor. The quantum chemical analysis reveals similarity in the absorption spectra of methyl-containing halogen derivatives which are characterized by four or five strong absorption bands in the spectral range 200-500 nm. A substitution of the methyl groups by the phenyl group causes the substantial changes of the absorption spectra mainly in the spectral range 240-370 nm. The comparison of measured and calculated absorption spectra manifests rather good agreement, namely in the part regarding the spectral positions of the first oscillator (absorption threshold). At the same time, the measured spectra reveal the considerable broadening almost of all absorption bands and even complete damping some of them in the case of phenyl derivatives. Semi-empirical PM3 method demonstrate substantially better agreement with the experimental values compared to the AM1 method. The lowest magnitude of the nonlinear optical susceptibility is revealed for Br-containing [PQ]-derivative. It is assumed that Br leads here to a suppressing of the charge transfers mechanism what is the reason for a relatively low nonlinear optical efficiency. (C) 2004 Elsevier B.V. All rights reserved.