Very recently, N-heterocyclic carbenes (NHCs) have found a wide range of applications in the fields of catalysis and nonlinear optics. Herein, we have employed 1,3-bis-(1(S)-benzyl)-4,5-dihydro-imidazol-based carbene as a reference molecule and substituted one H atom from each CH2 of the benzyl groups in both sides by CH3, NH2, and CF3 to study the thermodynamic and opto-electronic properties of NHCs theoretically. It was observed that the enthalpy (H), Gibb’s free energy (G), specific heat capacity (C v), and entropy (S) increase significantly in the presence of the electron-withdrawing groups compared to the electron-donating groups. The IR active in-plane bending vibrations of the CH (NHC) group are shifted to the higher frequency region for the considered substituted molecules compared to the reference carbene. The analysis of the electronic properties shows that the CH3-substituted carbene is more reactive for catalytic activities compared to other NHCs. The calculated nonlinear optical (NLO) properties reveal that the NH2-substituted NHC has the largest hyperpolarizability value whereas the CH3-substituted NHC has the largest dipole moment and polarizability among all, making them potential candidates for the development of NLO materials.

中文翻译：

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用于催化和非线性光学应用的 N-杂环卡宾的计算表征

最近，N-杂环卡宾（NHC）在催化和非线性光学领域得到了广泛的应用。在这里，我们采用了 1,3-bis-(1(S)-苄基)-4,5-二氢咪唑基卡宾作为参考分子，每个 CH 取代一个 H 原子2两侧的苄基均被CH取代3, NH2，和CF3从理论上研究NHCs的热力学和光电性质。据观察，热函（H), 吉布自由能 (G）、比热容（C v）和熵（S）与给电子基团相比，在吸电子基团存在下显着增加。与参考卡宾相比，对于所考虑的取代分子，CH (NHC) 基团的红外活性面内弯曲振动转移到更高的频率区域。电子性质分析表明CH3与其他 NHC 相比，-取代卡宾的催化活性更具反应性。计算的非线性光学 (NLO) 特性表明 NH2-取代的 NHC 具有最大的超极化率值，而 CH3-取代的NHC具有最大的偶极矩和极化率，使其成为NLO材料开发的潜在候选者。