Optical poling effect and optical absorption of cyan, ethylcarboxyl and tert -buthyl derivatives of 1H-pyrazolo[3,4-b]quinoline: experiment and quantum-chemical simulations

We present here results of experimental studies and quantum-chemical simulations of optical absorption and optical poling effects performed on a new synthesized cyan, ethylcarboxyl and tert -buthyl derivatives of 1H-pyrazolo[3,4-b]quinoline incorporated into polymer matrix or dissolved in organic solutions. The efficiency of second-order optical susceptibility d vs photoinduced power density Ip clearly saturates to certain magnitude deff at sufficient power densities (Ip≥ 1.3 GW cm−2). Comparing experimental data and results of semiempirical quantum-chemical simulations one can conclude that there exists generally a good correlation between the magnitude of saturated susceptibilities deff and macroscopic hyperpolarizabilities for all compounds except the chromophore 1,3-dimethyl-6-cyano-[PQ] only. The discrepancy for this compound may reflect a specific contribution of surrounding polymer matrix. According to the quantum chemical analysis the methyl-containing cyan and ethylocarcoxyl derivatives reveal four/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. Measured and calculated absorption spectra manifest rather good agreement mainly in the part regarding the spectral positions of the first oscillator (absorption threshold). The quantum-chemical PM3 method shows the best agreement with experiment. At the same time a considerable broadening almost of all absorption bands appears as a characteristic feature of all measured spectra. The discrepancies between the calculated and the measured spectra are attributed to electron-vibronic coupling as well as to a specific rotational dynamics of phenyl rings.