α、β-并三噻吩衍生物分子的二阶非线性光学性质
The second-order nonlinear optical natures of α、β-condensed three thiophene derivatives

采用密度泛函理论B3LYP/6-31+g(d)方法对二聚α、β-并三噻吩衍生物的18个分子(a～j2) 进行几何构型优化，对其最优构型采用TD-DFT(TDB3LYP/6-31+g(d))计算电子吸收光谱，用有限场FF方法及自编程序计算二阶非线性光学（NLO）性质。计算结果表明，增加共轭链的含乙烯桥的二聚并三噻吩比不含乙烯桥者，？μ(或？0)大1.6―5.3倍；在含乙烯桥二聚α、β-并三噻吩分子(母体分子) 末端引入含C=C或C≡C的基团（如-C≡CH与-C=C(CN)2），比引入强供电子基团（如-N(CH2CH3)2）、单纯吸电子基（如F原子）？μ(或？0) 更大；尤其是端接-C=C(CN)2基团的二聚α、β-并三噻吩衍生物，其？μ（或？0）值为104数量级个原子单位(10-29 esu)，与母体分子相比？μ增大4.8～19.6倍，更有利于改善体系的二阶非线性光学性质，从而可获得良好的非线性光学材料。
The most optimized geometrical configuration of 18 α,β condensed three thiophene derivatives molecules (a~j2) will be picked out by using density functional theroy B3LYP/6-31+g(d) method, the most optimized configurations TD-DFT ( TDB3LYP /6-31+g(d) ) will be applied to the calculation of electronic absorption spectrum , the second-order nonlinear optical property (NLO) will be calculated by using the FF method and the self-complied programs. Calculations indicate that the dimerization condensed three thiophene with ethylene bridge (conjugated chain) is 1.6―5.3 times stronger than those without ehtylene bridge in ？μ(？0). The perssad contains C≡C or C=C (such as -C≡CH and ？CC=C(CN)2) is more effective than strong electronic perssad ( such as ？CN(CH2 CH3)2) or pure electronic absorption perssad (such as F atom) in increasing ？μ(？0), when instroduced at the terminal of dimerization α,β condensed three thiophene(parent molecule) with ethylene bridge, especially the ？CC=C(CN)2 perssad。The value is 104 order of magnitude atomic unit(10-29 esu), which is 4.8~19.6 times larger than that of the parent molecule. Therefore, the second-order nonlinear optical property of system can be improved greatly by using the method mentioned above, so that the better nonlinear optical materials can be achieved.