Theoretical study on static (hyper)polarizabilities for polyimide by the elongation finite-field method

The elongation finite-field method is applied to calculate (hyper)polarizabilities of polyimides PMDA/DMDB, PMDA/ODA, and PMDA/TFDB. The nonlinear optical (NLO) properties of planar structures of three polyimides are compared to those of their twist structures. It is found that all and values of the planar structures are larger than the corresponding values of the twist structures, which may be attributed to the fact that -conjugation of twist structures is decreased compared with the planar structures. All values of planar and twist structures oscillate regularly along with elongating the chain. Moreover, effect of two side-groups -CH3 and -CF3 on the NLO properties of PMDA/DMDB and PMDA/TFDB is investigated.