Theoretical study on the effect of spacer groups on the nonlinear optical properties of polyvinyl carbazole molecular fragments

In this paper, polyvinyl carbazole fragments with side-hung chromogenic groups were used as the parent. The relationship between the structure and the properties of NLO was studied by changing the type of spacer groups on chromogenic groups with density functional theory (DFT). The results show that all designed systems have significant second-order NLO response. The first hyperpolarizability ( β 0 ) of the system has the following regularity (taking PBE0 algorithm as an example): the β 0 value of the system is related to the type of electron-donating and electron-withdrawing spacer group (X).The β 0 value of electron-donating spacer group is larger than that of electron-withdrawing spacer, and the β 0 value of the molecule is independent of the size of the spacer group. When the spacer group is methyl, the value of β 0 (168.1 × 10 −30 esu) is the largest in tested electron-donating group. When the spacer group is an electron-withdrawing group, the value of β 0 is related to electron-withdrawing ability, and the value of β 0 is inversely proportional to the electron-withdrawing ability of the spacer group.