Objective: Two novel Schiff bases named, 2-((2-Hydroxybenzylidene)amino)-4,5,6,7- tetrahydrobenzo[b] thiophene-3-carbonitrile (BESB1) and 2-((Furan-2-ylmethylene)amino)-4,5,6, 7-tetrahydro-benzo[b]thiophene-3-carbonitrile (BESB2) were synthesized.

Methods: The structures were characterized based on CHN elemental analysis, mid-infrared (400– 4000 cm-1), Raman (100-4000 cm-1), 1H NMR, mass and UV-Vis spectroscopic measurements. In addition, quantum mechanical calculations using DFT-B3LYP method at 6-31G(d) basis set were carried out for both Schiff bases. Initially, we have carried out complete geometry optimizations followed by frequency calculations for the proposed conformational isomers; BESB1 (A–E) and BESB2 (F–J) based on the orientations of both CN and OH groups against the azomethine lonepair (NLP) in addition to the 3D assumption.

Results: The computational outcomes favor conformer A for BESB1 in which the C≡N and OH moieties are cis towards the NLP while conformer G is preferred for BESB2 (the C≡N/furan-O are cis/trans towards the NLP) which was found consistent with the results of relaxed potential energy surface scan. Aided by normal coordinate analysis of the Cartesian coordinate displacements, we have suggested reliable vibrational assignments for all observed IR and Raman bands. Moreover, the electronic absorption spectra for the favored conformers were predicted in DMSO solution using TD-B3LYP/6-31G(d) calculations. Similarly, the 1H NMR chemical shifts were also estimated using GIAO approach implementing PCM including solvent effects (DMSO-d6).

Conclusion: Proper interpretations of the observed electronic transition, chemical shifts, IR and Raman bands were presented in this study.

目的：两个新的席夫碱命名为2-（（2-羟基苄叉基）氨基）-4,5,6,7-四氢苯并[b]噻吩-3-腈（BESB1）和2-（（呋喃-2-基亚甲基）合成了氨基）-4,5,6,7-四氢-苯并[b]噻吩-3-腈（BESB2）。

方法：根据CHN元素分析，中红外（400–4000 cm-1），拉曼（100-4000 cm-1），1H NMR，质量和UV-Vis光谱测量对结构进行表征。此外，对两个席夫碱均使用DFT-B3LYP方法在6-31G（d）基组上进行了量子力学计算。最初，我们对拟议的构象异构体进行了完整的几何优化，然后进行了频率计算。BESB1（AE）和BESB2（F–J）除了3D假设外，还基于CN和OH基团对偶氮甲碱孤对（NLP）的取向。

结果：计算结果偏向于BESB1的构象异构体A，其中C≡N和OH部分为NLP的顺式，而对于BSBSB2则优选构象异构体G（C≡N/呋喃-O为NLP的顺式/反式）。发现与松弛势能表面扫描的结果一致。通过对笛卡尔坐标位移进行正态坐标分析，我们为所有观察到的IR和拉曼波段建议了可靠的振动分配。此外，使用TD-B3LYP / 6-31G（d）计算在DMSO溶液中预测了偏爱的构象异构体的电子吸收光谱。同样，还使用GIAO方法估算了1H NMR化学位移，该方法实现了包括溶剂效应（DMSO-d6）的PCM。

结论：本研究提出了对观察到的电子跃迁，化学位移，IR和拉曼谱带的正确解释。