Rational design of the nonlinear optical materials dinaphtho[2,3-b:2′,3′-d]thiophene-5,7,12,13-tetraone (DNTTRA) and its phenyldiazenyl derivatives using first-principles calculations

Abstract

Using density functional theory (DFT) at the M06-2X level with the 6-311++g(d,p) basis set, the structure, frontier orbitals, and second-order nonlinear optical (NLO) properties of dinaphtho[2,3-b:2′,3′-d]thiophene-5,7,12,13-tetraone (DNTTRA) and 18 of its phenyldiazenyl derivatives are calculated. The electronic absorption spectra are calculated by time-dependent density functional theory (TD-DFT) using the TD-M06-2X method. The results show that the strongest absorption peak of the 19 molecules lies in the range of 258.8–416.1 nm. When the 2, 10 sites of the DNTTRA molecule are substituted by phenyldiazenyl groups, the maximum absorption peak is red-shifted significantly compared with substitutions at the 3, 9 and 2, 9 sites. In addition, the second-order NLO properties (β0, βµ) are increased by 22 and 2 times more compared with the substitutions at the 3, 9 and 2, 9 positions, indicating that substitution of phenyldiazenyl groups at the 2, 10 sites is superior to substitution at the 3, 9 and 2, 9 sites for the DNTTRA molecule. Moreover, substitution of strong electron-donor groups [such as –NHCH3 or –N(CH3)2] at the opposite end of the phenyldiazenyl rings is found to be beneficial to improve the second-order NLO properties of the system, resulting in second-order NLO materials with excellent performance.