Dengiz Çağatay
Department of Chemistry, Middle East Technical University, Ankara Turkey.
Turk J Chem. 2021 Oct 19;45(5):1375-1390. doi: 10.3906/kim-2102-22. eCollection 2021.
A series of new push-pull chromophores were synthesized in moderate to very high yields (65%-97%) by treating TCNE and TCNQ with alkynes substituted by electron-rich diethylaniline and polycyclic aromatic hydrocarbons. Some of the chromophores exhibit strong intramolecular charge-transfer bands in the near-IR region with λ values between 695 and 749 nm. With the help of experimental and theoretical analysis, it is concluded that the trend in values is affected by PAH substituents sterically, not electronically. Steric constraints led to the increased dihedral angles, reducing conjugation efficiencies. The absorption properties of push-pull compounds have been investigated in solvents possessing different polarities. All chromophores exhibited positive solvatochromism. As an additional proof of efficient charge-transfer in push-pull chromophores, quinoid character (d) values were predicted using calculated bond lengths. Remarkably, substantial d values (0.045-0.049) were predicted for donor diethylaniline rings in all compounds. The effects of various polycyclic aromatic hydrocarbons on optical and nonlinear optical properties were also studied by computational methods. Several parameters, such as band gaps, Mulliken electronegativity, chemical hardness and softness, dipole moments, average polarizability, first hyperpolarizability, were predicted for chromophores at the B3LYP/6-31++G(d,p) level of theory. The predicted first hyperpolarizability β values vary between 198 to 538 × 10 esu for the reported push-pull chromophores in this study. The highest predicted β value in this study is 537.842 × 10 esu, 8150 times larger than the predicted β value of benchmark NLO material urea, suggests possible utilization of these chromophores in NLO devices. The charge-transfer character of the synthesized structures was further confirmed by HOMO-LUMO depictions and electrostatic potential maps.
通过用富含电子的二乙胺和多环芳烃取代的炔烃处理四氰基乙烯（TCNE）和四氰基对苯二醌（TCNQ），以中等至非常高的产率（65%-97%）合成了一系列新型推拉发色团。一些发色团在近红外区域表现出强的分子内电荷转移带，λ值在695至749nm之间。借助实验和理论分析，得出结论：λ值的趋势受多环芳烃取代基的空间影响，而非电子影响。空间限制导致二面角增大，降低了共轭效率。在具有不同极性的溶剂中研究了推拉化合物的吸收特性。所有发色团均表现出正溶剂化显色性。作为推拉发色团中有效电荷转移的额外证据，使用计算出的键长预测了醌型特征（d）值。值得注意的是，预测所有化合物中供体二乙胺环的d值相当大（0.045-0.049）。还通过计算方法研究了各种多环芳烃对光学和非线性光学性质的影响。在B3LYP/6-31++G(d,p)理论水平下，预测了发色团的几个参数，如带隙、穆利肯电负性、化学硬度和柔软度、偶极矩、平均极化率、第一超极化率。本研究中报道的推拉发色团的预测第一超极化率β值在198至538×10 esu之间变化。本研究中预测的最高β值为537.842×10 esu，比基准非线性光学材料尿素的预测β值大8150倍，表明这些发色团可能用于非线性光学器件。通过HOMO-LUMO描述和静电势图进一步证实了合成结构的电荷转移特性。
