Enhanced nonlinear optical properties of porphyrin with an extended π-conjugated bridge

Abstract

In this work, a series of molecules with an extended π-conjugated bridge have been theoretically designed based on porphyrin, where -(CH=CH)n- (n = 1–4, 8, 12) chain is served as an extended π-conjugated bridge. It is found that all molecules exhibit large energy gaps in the range of 3.484–4.151 eV for porphyrin-(CH=CH)n-NH2, and 3.624–4.250 for porphyrin-(CH=CH)n-NO2. The maximum absorption wavelengths of all molecules show a red shift trend with increasing -(CH=CH)n- length, which leads to small transition energy. It is observed that long chain brings these molecules the large first hyperpolarizability, which are 1.04 × 105 au for porphyrin-(CH=CH)12-NH2, 1.26×105 au for porphyrin-(CH=CH)12-NO2. Moreover, compared with -(CH=CH)n-NH2 with the same chain length, -(CH=CH)n-NO2 chain can achieve larger nonlinear optical response. It is hoped that the research in this paper can provide a new strategy for the experimental design of nonlinear optical materials.