半花菁衍生物分子第一超极化率频率色散效应的理论研究

采用含时耦合微扰(TDHF)和多态求和(SOS)方法计算了半花菁衍生物分子生色团4-N,N-dimethylami-no-4′-N′-methylstilbazolium(DAS)的第一超极化率频率色散效应。采用组态相关(INDO/CI)方法计算了分子的前线轨道性质。计算结果表明半花菁衍生物分子最大吸收波长约为480nm,与实验结果十分吻合;第一激发态对体系非线性光学性质起决定作用。在红外波段(800~2500nm),随着基频光频率的增大,二次谐波β(-2ω;ω,ω)和电光效应β(-ω;ω,0)都随之增大,但是β(-2ω;ω,ω)增加的幅度要大于β(-ω;ω,0)。在远红外区β(-2ω;ω,ω)的色散曲线变化比较平缓,到了近红外区(λ<1300nm)共振增强效应逐渐明显。基频光波长为1064nm时,β(-2ω;ω,ω)的含时耦合微扰计算值约为(380±5)×10-30esu。在较高频率时,采用多态求和方法计算应考虑其他态的贡献。此外,还讨论了基组效应对含时耦合微扰计算的影响。

Theoretical Studies on Frequency-Dispersion Effect of First Hyperpolarizabilities of Hemicyanine Derivatives

The first hyperpolarizabilities β(-2ω;ω,ω) and β(-ω;ω,0) of hemicyanine derivatives chromophore, 4-N,N-dimethylamino-4'-N'-methyl stilbazolium (DAS), are calculated by using time-dependent Hartree-Fock (TDHF) and sum over states (SOS) method at infrared wavelength, respectively. Frontier molecular orbitals are also computed by INDO/CI method. The numerical results indicate that maximum absorption wavelengh is about 480 nm which agrees well with the experimental data, and nonlinear optical properties are determined by the first excited state. In infrared region (800～2500 nm), with the increase of fundamental frequency, secondary harmonic generation (SHG) β(-2ω;ω,ω) and electrooptic effect (EOE) β(-ω;ω,0) also become larger, but β(-2ω;ω,ω) increased greater than β(-ω;ω,0). In off-infrared region, β(-2ω;ω,ω) dispersion curve is flat while sharp caused by resonance enhancement in near-infrared region (<1300 nm). β(-2ω;ω,ω) equals to (380±5)×10-30 esu at 1064 nm calculated by TDHF. However, for the higher frequency, other excited states should be considered in SOS calculation. Moreover, influence of basis set effect upon TDHF calculation is also discussed.