New Y-shaped ferrocene (Fc) conjugated trifluoromethyl substituted imidazole (IM) donor-π-acceptor [(D-π)₂-IM-D′-π-CF₃] “push-pull” chromophores [(Fc-CH=CH)₂-IM-C₆H₄-R-C₆H₄-CF₃] {R= -OCH₃ (1); -N(C₂H₅)₂ (2)} were synthesized and structurally characterized. The structure of the chromophores was confirmed by single crystal X-ray diffraction studies. They crystallized in triclinic with P-1 (for 1) and monoclinic with P21/c (for 2) space group. Thermogravimetric analysis (TGA) was used to study the thermal stability of chromophores 1 and 2, and it was found that both were stable at temperatures of about 300 °C. The redox properties were studied by cyclic voltammetry (CV), which revealed one-electron transfer from the ferrocene to ferrocenium ion (Fe²⁺↔Fe³⁺), and potentials were utilized to calculate the energy gap (that is 2.16 eV for 1 and 2.12 eV for 2). The second order nonlinear optical (NLO) properties of the chromophores 1 and 2 were explored by Electric-Field-Induced Second Harmonic generation (EFISH) technique in CHCl₃ solution with an incident wavelength of 1907 nm. μβ_EFISH value are: −725 ×10^-48 esu and −806 ×10^-48 esu, for (1) and (2) respectively. The μβ_EFISH values were feebly decreased, compared with reported ferrocene conjugated Y-shaped imidazole chromophores, due to the substitution on imidazole nitrogen, which increases the steric hindrance and reduces the ICT process in the chromophores. In addition, frontier molecular orbital levels, excited and ground state dipole moments (μ_e and μ_g), and electronic absorption spectra were studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) with B3LYP method using 6-31+G** as basis set.

中文翻译：

---

取代对二茂铁附加供体-π-受体Y型三氟甲基咪唑发色团二阶非线性光学性质的影响


新型Y型二茂铁(Fc)共轭三氟甲基取代咪唑(IM)供体-π-受体[(D-π) ₂ -IM-D′-π-CF ₃ ] “推拉”发色团 [(Fc-CH=CH) ₂ -IM-C ₆ H ₄ -R-C ₆ H ₄ -CF ₃ ] {R= -OCH ₃ (1);合成了-N(C ₂ H ₅ ) ₂ (2)}并进行了结构表征。通过单晶 X 射线衍射研究证实了发色团的​​结构。它们结晶为三斜晶系的P-1（对于1）和单斜晶系的P21/c（对于2）空间群。采用热重分析（TGA）研究了发色团1和2的热稳定性，发现两者在300℃左右的温度下都很稳定。通过循环伏安法（CV）研究了氧化还原性质，揭示了从二茂铁到二茂铁离子（Fe ²⁺ ↔Fe ³⁺ ）的单电子转移，并利用电势计算能隙（即 1 为 2.16 eV，2 为 2.12 eV）。在入射波长为 1907 nm 的 CHCl ₃ 溶液中，通过电场诱导二次谐波发生 (EFISH) 技术探索了发色团 1 和 2 的二阶非线性光学 (NLO) 性质。对于（1）和（2），μβ _EFISH 值分别为：-725 ×10 ^-48 esu 和 -806 ×10 ^-48 esu。与报道的二茂铁共轭Y形咪唑生色团相比，μβ _EFISH 值略有降低，这是由于咪唑氮上的取代增加了生色团的空间位阻并减少了ICT过程。 此外，还通过密度泛函理论（DFT）和时间-研究了前沿分子轨道能级、激发态和基态偶极矩（μ _e 和 μ _g ）以及电子吸收光谱。依赖密度泛函理论 (TD-DFT)，采用 B3LYP 方法，使用 6-31+G** 作为基础集。