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采用密度泛函理论(DFT)结合有限场(FF)方法,对不同共轭桥连接的四氰代二甲基苯醌(TCNQ)开壳层和闭壳层电子态的非线性光学(NLO)系数进行计算,并以乙烯桥为例讨论共轭链长度与NLO性质的关系.结果表明:开壳层体系的极化率和二阶超极化率值都大于闭壳层体系,且共轭桥的共轭性越强,体系的极化率和二阶超极化率越大;在自由基体系中,单重态的二阶超极化率随双自由基成分y和自旋多重度的增加而增大.体系的共轭链增长,BLA(BondLength Alternation,共轭分子中相邻单、双键键长差的平均值)逐渐减小,双自由基成分y逐渐增大,体系的二阶超极化率也逐渐增大.
The nonlinear optical (NLO) spectra of open and closed shell states of tetracyanoquinodimethane (TCNQ) with different conjugated bridges were investigated by using density functional theory (DFT) combined with finite field (FF) The relationship between the length of conjugated chain and the NLO properties was discussed by taking the vinyl bridge as an example.The results showed that both the polarizability and the second-order hyperpolarizability of the open-shell system were greater than that of the closed-shell system, and the conjugation The higher the conjugation of the bridge, the higher the polarizability and the second-order hyperpolarizability of the system. In the free radical system, the second-order hyperpolarizability of the singlet state varies with the diradical content y and spin multiplicity The increase of conjugate chain, the BLA (BondLength Alternation, the average value of the difference between adjacent single and double bond in the conjugate molecule) decreases gradually, the diradical component y increases gradually, The second-order hyperpolarizability also increases gradually.