Computational Study on Redox-Switchable 2D Second-Order Nonlinear Optical Properties of Push−Pull Mono-tetrathiafulvalene-Bis(Salicylaldiminato) Zn(II) Schiff Base Complexes
journal contributionposted on 2011-04-07, 00:00 authored by Chun-Guang Liu, Xiao-Hui Guan, Zhong-Min Su
The redox-switchable 2D second-order nonlinear optical (NLO) property of a series of tetrathiafulvalene (TTF) derivatives has been studied based on the density functional theory (DFT) calculations. The redox-active TTF unit has been considered as a manipulative center for switching the 2D second-order NLO properties. Our DFT calculations show that introduction of the TTF unit cannot effectively enhance the second-order NLO properties relative to the reference system 1 because the nonplane embowed arrangement of the TTF unit reduces the electron donor capacity. The electronic structure analysis shows that the TTF unit acts as the oxidized center in one- and two-electron-oxidized processes for 5. A significant transformation on the structure of the TTF unit, the TTF unit changes from the embowed structure to a planar structure, has been found in the series of oxidized processes according to DFT-optimized calculations. This leads to the low excited energy and different charge transfer features of the oxidized species relative to its reduced parents, and thus enhances the static first hyperpolarizabilities. The β value of one- and two-electron-oxidized species is at least ∼15 and ∼8.6 times as large as that of its reduced parents according to our DFT calculations. Simultaneously, the oxidized process increases the contributions from the y-polarized transition, and thus improves the 2D second-order NLO property.