Computational analysis of first hyperpolarizability of heterocyclic rigid-rod molecules

• Main Authors: Hao-Jie Mo, 莫皓傑
• Other Authors: Tzu-Chien Hsu
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/9vr5r2

碩士 === 國立中山大學 === 材料科學研究所 === 96 === The first hyperpolarizability β, which is an important factor in the second-order nonlinear optical effect, of the 5-6-5 heterocyclic rigid-rod chromophores-based derivatives has been systematically investigated in this work, applying the first principle based software CASTEP and the semi-empirical software MOPAC There are four factors chosen for this computational analysis, including the effects of (i) various rigid-rod molecules, (ii) auxiliary ability of various five-member rings, (iii) donor ability, and (iv) conjugation length. Results indicate that the benzobisimidazole (BBI)-based derivatives have larger β values than those of benzobisthiazole (BBT) and benzobisoxazole (BBO)-based derivatives. The auxiliary donor ability of the pyrrole is larger than that of the thiophene and furan. In general, the β value of various derivatives studied is parallel to the original donor strength and the trend in the donor is -N(CH3)2 > -NH2 > -OH > -CH3. In addition, the greater the conjugation length in the derivatives is, the higher the β value. Further, from the analyses on the band-resolved β values and the orbital density figures, it is found that the major contribution to the enhanced β comes primarily from an efficient charge transfer from the donor side via the intermediate heterocyclic bridge to the acceptor side. Finally, a comparison between CASTEP and MOPAC reveals that CASTEP is more appropriate and accurate in predicting the optical properties of the heterocyclic-ring-based derivatives.