Third-order nonlinear optical properties of phenothiazine-based imine covalent organic framework films

Abstract

The manipulation of the chemical structure within covalent organic frameworks (COFs) is emerging as a potent approach to engineering materials with enhanced charge transfer efficiency and nonlinear optical (NLO) properties. This study introduces the synthesis of two donor-acceptor (D-A) COF films, PB-TZ and PT-TZ, via solvothermal processing, followed by a detailed examination of their third-order NLO characteristics. Notably, COF films demonstrated Saturation absorption and self-defocusing properties at a 532 nm laser irradiation, indicating their potential utility in optical applications. The third-order nonlinearly polarized magnetic induction (χ(3)) of the PT-TZ film is significantly higher compared with that of the PB-TZ film, reaching 16.05 ± 0.17 × 10−7 esu, which is 2.9 times higher than that of the PB-TZ film. This enhancement can be attributed to the superior acceptor ability of the triazine ring within PT-TZ, which promotes a more efficient electron transfer from the donor to the acceptor units. Consequently, this study provides a new idea for the development of COF films in the field of high-performance NLO.