THEORETICAL INVESTIGATION ON SECOND-ORDER NONLINEAR OPTICAL PROPERTIES AND REDOX-SWITCHING OF PHENYL NITRONYL-NITROXIDE RADICAL DERIVATIVES

Abstract

The static second-order nonlinear optical (NLO) properties on a series of phenyl nitronyl-nitroxide (NN) radical derivatives were investigated using density functional theory (DFT). It is found that the first hyperpolarizabilities of these systems are sensitive to the substituents, and system 4a containing of a two-dimensional (2D) substituent possesses the largest βtot value of 83.134 × 10-30 esu. Meanwhile, the time-dependent (TD)-PBE1PBE calculations indicate that low transition energy can enhance the NLO responses. As a result of the reversible one-electron oxidizations of these systems, the redox switching of the NLO responses of systems 1a–5a have also been studied. The βtot value of system 2b′ is about 20.75 times larger than that of 2a due to the larger degree of conjugation, which provides a possibility of NLO switching. According to the analysis of the frontier molecular orbitals (FMO), oxidization reduces the HOMO–LUMO gap and changes charge transfer (CT) direction.