Above-room-temperature switching of quadratic nonlinear optical properties in a Bi–halide organic–inorganic hybrid

A lead-free Bi-based organic–inorganic hybrid shows attractive above-room-temperature NLO switching behaviors with a superior contrast of ∼35.

THEORETICAL INVESTIGATION ON PHOTOISOMERIZATION SWITCHABLE SECOND-ORDER NONLINEAR OPTICAL PROPERTIES OF Λ-SHAPED DIARYLETHENE DERIVATIVES

The nonlinear optical (NLO) properties of Λ-shaped diarylethene (DAE) derivatives 1a(b)–4a(b) and their NLO switching effects were studied by using the density functional theory (DFT) methods. The results demonstrate that all of the open-ring molecules and their own closed-ring forms meet the model of NLO switching tuned by photoisomerization. The βtot values of 1b–3b are 16 times as small as that of their open-ring forms, and βtot value of 4b is 4 times as large as that of 4a. The spin interactions of open-shell closed-ring molecules are larger than that of their open-ring forms, and it could increase the NLO responses to some degree. Nature bond orbital (NBO) calculations indicate that large charge differences between electron-deficient and electron-rich centers are beneficial to charge transfer (CT), and the overlap between frontier molecular orbital (FMO) is also advantageous to the CT and NLO responses. Time-dependent density functional theory (TD-DFT) calculations show βtot values of all molecules meet the two-level model very well, and the smaller the ΔE ge , the larger the βtot value.

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

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.