Theoretical Study Of Third-order Nonlinear Optical Properties Of Annulenes Derivativities

Nonlinear optics mainly study the nonlinear phenomena generated by strong effect of coherent light with the media. So far, many attentions have been to access new type organic nonlinear optics materials. Annulene derivatives have been the focus of research in recent years because of their excellent nonlinear optical properties. Based on the theory of quantum chemistry, the factors that influence the third-order nonlinear response of annulene derivatives, such as different substituents, conjugation length, frequency dispersion effect, solvent effect and so on, have been investigated. The results will provide a guideline for designing and composing high effective nonlinear optics molecules. The main results are presented as following:1. The effects of conjugation system, substituents and frequency on nonlinear properties of annulenes derivatives have been studied. The molecular static linear polarizabilities a and second hyperpolarizabilities g of substituted annulenes have been investigated with different levels of HF, B3 LYP, BHand HLYP and CAM-B3 LYP at different basis sets, respectively. Their ultraviolet spectra have also calculated by using TD-B3 LYP method. We found that the quality of the basis set is important for the hyperpolarizability calculations, and diffuse functions are important to obtain accurate results for the second hyperpolarizability. We also study the structure-optical properties relationship for annulenes. It is found that annulenes molecular structures have significant impact on third-order nonlinear optical response. Increasing the conjugation length and introducing push-pull electronic groups can enhance the second hyperpolarizability. But the introduction of push-pull electronic groups can enhance the hyperpolarizability more remarkably than increasing the conjugation length dose. The reason may be that the introduction of push-pull electronic groups can provide a large number of polarizable electrons whereas increasing the conjugation length can only higher electron delocalization. Meanwhile the push-pull electronic group substituted annulenes can also exhibit high transparency in visible region. Thus, this work has a good reference guide for the design of nonlinear optical materials with high nonlinear optical coefficient and good transparency. In addition, for the same push-pull electronic groups, the higher conjugation degree and the longer p-conjugated bridge result in the decrease of HOMO-LUMO energy gap and transition energy which benefits the enhancement of nonlinear optical response. Our results demonstrate that annulenes derivatives show both high transparency and large second hyperpolarizability, and thus become promising candidates for third-order NLO materials. In addition, the dynamic(hyper)polarizabilites of considered annulenes molecule are calculated by using CAM-B3 LYP method, respectively. It is found that in near infrared region, with the increase of frequency of incident light, a(w;w), g(-w;w, 0, 0) and g(-2w;w,w, 0) are all increased, and the near resonance enhancement effect occurs. Under the condition of far resonance, a(w;w), g(-w;w, 0, 0) and g(-2w;w,w, 0) have little change.2. The effect of solvent on nonlinear properties of annulene derivatives has been studied. The geometric configurations, polarizabilities and hyperpolarizabilities of annulene derivatives molecules in gas and other 16 kinds of solvents at 6-31+G(d) basis set have been calculated with CAM-B3 LYP method. The calculated results indicate that the molecular configuration has slight difference in different solvents. However, the slight difference of molecular structures has have significant impact on nonlinear optical properties of molecules. In addition, the effect of solvents on molecular frontier orbital energy gap has been investigated. The calculation shows that the changes of orbital energy difference HLDE with the increasing dielectric constant e decreases rapidly with small e( e <25), and it changes slightly in the solvent with the dielectric constant larger 25. Consequently, the nonlinear polarizability increases with the increase of e when e is small, then it become convergent at larger e. Compared to vacuum, the geometric configuration, charge distribution, molecular and spectral properties of molecule have changes in different degrees in different solvents. Therefore, the solvent effect is important to the nonlinear optical properties of annulene molecules.