Abstract
The switching of second-order nonlinear optical (NLO) properties for a tetrathiafulvalene (TTF) derivative across the six stable states has been studied by using the density Emotional theory (DFT) calculations. The redox-active TTF unit and a photoisomerized chromophore 1,2-dithienylperfluorocyclopentene (DTE) have been implemented to switch the second-order NLO responses. Our DFT calculations with three functionals demonstrate that introduction of the DTE moiety into the pi-conjugated bridge can significantly enhance the second-order NLO response relevant to the donor/acceptor end in this work. Our DFT calculations illustrate that photoisomerization bring forth a large change in the geometry of the series of compounds. The closed-ring form possesses a good pi-conjugation relative to the open-ring form and thus a large second-order NLO response. The electronic structure analysis shows that the TTF unit will perform as an oxidation center in the one- and two-electron-oxidation processes. The one- and two-electron-oxidized species have better planar structures of TTF unit than its neutral compound, which ultimately leads to the low excited energy and enhances the static first hyperpolarizability. Our present DFT calculations using three functionals show that the TTF derivative 4 can switch the second-order NLO properties across six stable states, which is a rare example in previously reported second-order NLO switches.