Bibi Amna, Muhammad Shabbir, UrRehman Shafiq, Bibi Shamsa, Bashir Shahid, Ayub Khurshid, Adnan Muhammad, Khalid Muhammad
Department of Chemistry, University of Agriculture Faisalabad, Faisalabad 38000, Pakistan.
Department of Physics, College of Science, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia.
ACS Omega. 2021 Sep 13;6(38):24602-24613. doi: 10.1021/acsomega.1c03218. eCollection 2021 Sep 28.
In the present investigation, quantum chemical calculations have been performed in a systematic way to explore the optoelectronic, charge transfer, and nonlinear optical (NLO) properties of different bis(dicyanomethylene) end-functionalized quinoidal oligothiophenes. The effect of different conformations (linking modes of thiophene rings) on conformational, optoelectronic, and NLO properties are studied from the best-performed dimer to octamer. The optical and NLO properties of all the selected systems () are calculated by means of density functional theory (DFT) methods. Among all the designed compounds, the largest linear isotropic (α) polarizability value of 603.1 × 10 esu is shown by compound which is ∼12, ∼16, ∼9, ∼11, ∼10, and ∼4 times larger as compared to compounds , respectively. A relative investigation is performed considering the expansion in third-order NLO polarizability as a function of size and conformational modes. Among all the investigated systems, system shows the highest value of static second hyperpolarizability ⟨γ⟩ with an amplitude of 7607 × 10 esu at the M06/6-311G** level of theory, which is ∼521, ∼505, ∼38, ∼884, ∼185, and ∼15 times more than that of compounds , respectively. The extensively larger ⟨γ⟩ amplitude of compound with higher oscillator strength and lower transition energy indicates that NLO properties are remarkably dependent upon linking modes of thiophene rings and its chain length. Furthermore, to trace the origin of higher nonlinearities, TD-DFT calculations are also performed at the same TD-M06/6-311G** level of theory. Additionally, a comprehensive understanding of the effect of structure/property relationship on the NLO polarizabilities of these investigated quinoidal oligothiophenes is obtained through the inspection of Frontier molecular orbitals, the density of states (TDOS and PDOS), and molecular electrostatic potential diagrams including the transition density matrix. Hence, the current examination will not just feature the NLO capability of entitled compounds yet additionally incite the interest of experimentalists to adequately modify the structure of these oligothiophenes for efficient optical and NLO applications.
在本研究中，已系统地进行了量子化学计算，以探索不同双（二氰基亚甲基）末端官能化醌式低聚噻吩的光电、电荷转移和非线性光学（NLO）性质。从性能最佳的二聚体到八聚体，研究了不同构象（噻吩环的连接方式）对构象、光电和NLO性质的影响。所有选定体系的光学和NLO性质均通过密度泛函理论（DFT）方法计算。在所有设计的化合物中，化合物显示出最大的线性各向同性（α）极化率值603.1×10 esu，分别比化合物大12、16、9、11、10和4倍。考虑到三阶NLO极化率随尺寸和构象模式的扩展进行了相关研究。在所有研究的体系中，体系在M06/6-311G理论水平下显示出最高的静态二阶超极化率⟨γ⟩值，幅度为7607×10 esu，分别比化合物大521、505、38、884、185和15倍。化合物具有更大的⟨γ⟩幅度、更高的振子强度和更低的跃迁能量，这表明NLO性质显著依赖于噻吩环的连接方式及其链长。此外，为了追踪更高非线性的起源，还在相同的TD-M06/6-311G理论水平下进行了含时密度泛函理论（TD-DFT）计算。此外，通过检查前线分子轨道、态密度（TDOS和PDOS）以及包括跃迁密度矩阵的分子静电势图，全面了解了结构/性质关系对这些研究的醌式低聚噻吩的NLO极化率的影响。因此，当前的研究不仅将突出所述化合物的NLO能力，还将激发实验人员的兴趣，以便为高效的光学和NLO应用充分修饰这些低聚噻吩的结构。
