Cariati E, Liu X, Geng Y, Forni A, Lucenti E, Righetto S, Decurtins S, Liu S-X
Department of Chemistry, Università degli Studi di Milano, INSTM UdR of Milano, via Golgi 19, 20133 Milano, Italy.
Phys Chem Chem Phys. 2017 Aug 23;19(33):22573-22579. doi: 10.1039/c7cp04687a.
The second-order nonlinear optical (NLO) properties of two tetrathiafulvalene (TTF)-fused electron donor-acceptor dyads have been determined using the Electric Field Induced Second Harmonic generation (EFISH) technique and theoretically rationalized. Dyads TTF-dppz (1) and TTF-BTD (2) were obtained by direct fusion of a TTF electron donor unit either with a dipyrido[3,2-a:2',3'-c]phenazine (dppz) or a benzothiadiazole (BTD) electron acceptor moiety. Dyad 1 acts as a reversible acido-triggered NLO switch by protonation/deprotonation at two nitrogen atoms of the dppz acceptor moiety induced by sequential exposure to HCl and ammonia vapors. Dyad 2, on the other hand, displays redox-tunable NLO properties upon two consecutive oxidations to its radical cation 2+˙ and dication 22+ species. The resulting final dication 22+ exhibits an inversion of the sign of β, due to a completely inverted distribution of the frontier molecular orbitals with respect to those of its neutral species, leading to a scarcely polar species in the excited state, as indicated by the theoretical calculations.
利用电场诱导二次谐波产生（EFISH）技术测定了两种四硫富瓦烯（TTF）稠合的电子供体-受体二元化合物的二阶非线性光学（NLO）性质，并进行了理论合理化分析。二元化合物TTF-dppz（1）和TTF-BTD（2）是通过将TTF电子供体单元与二吡啶并[3,2-a:2',3'-c]吩嗪（dppz）或苯并噻二唑（BTD）电子受体部分直接稠合而得到的。二元化合物1通过依次暴露于HCl和氨气中，在dppz受体部分的两个氮原子处进行质子化/去质子化，作为一种可逆的酸触发NLO开关。另一方面，二元化合物2在连续两次氧化为其自由基阳离子2+˙和二价阳离子22+物种时表现出氧化还原可调谐的NLO性质。理论计算表明，最终生成的二价阳离子22+由于其前沿分子轨道相对于中性物种的分子轨道完全反转，导致β符号反转，从而在激发态形成一个几乎无极性的物种。
