Abstract The present study spotlights the key structure-property features of a chalcone derivative (2E) 3-(4-ethoxyphenyl)-1-(3-bromophenyl) prop-2-en-1-one (E3BC) for future applications in nonlinear optical devices through dual approach involving experimental and theoretical techniques. The sample has been characterized by 1H NMR, FT-IR, FT-Raman and terahertz spectroscopies. The experimental results are supported by computational studies using density functional theory. To analyse the 1H NMR spectra, theoretical calculations on chemical shifts were done by GIAO method. Complete vibrational assignments of the vibrational modes have been made on the basis of the potential energy distribution in terms of internal coordinates. The low frequency vibrational modes between 0.2 and 1.8 THz were examined via terahertz time domain spectroscopy. The UV–vis spectrum was recorded in methanol solution. The energies, absorption wavelengths and oscillator strengths of electronic singlet-singlet transitions were determined by time dependent density functional theory. The calculated HOMO-LUMO energy gap is small which reveals that the charge transfer takes place within the molecule and it can be exploited for the nonlinear optical applications. Information about the charge density distribution and the sites of chemical reactivity of the molecule has been obtained by mapping electron density with molecular electrostatic potential. The MEP surface around the bromine atom exhibited the dual nature. Along the C-Br axis the positive electrostatic potential (the σ-hole) is present while the remainder of the surface is negative. Hence bromine atom can interact electrostatically with both nucleophiles and electrophiles. For other atoms no atom-specific effects are found. The stability of the molecule arising from hyper conjugative interactions and charge delocalization has been interpreted using natural bond orbital analysis. The study indicates that the intramolecular charge transfer (n → σ∗, n → π∗ and π → π∗) can induce nonlinearity in the molecule and validates E3BC's candidature to be used as a nonlinear optical active material. In order to understand the nonlinear optical activity of the molecule the calculations of electronic dipole moment, polarizability, anisotropy of polarizability as well as first and second hyperpolarizabilities are performed using finite field approach implemented in the DFT method. The findings suggested that the first order hyperpolarizability of titled molecule is 139 times greater than the value of urea. The high value of first order hyperpolarizability shows that E3BC can be a potential candidate in the nonlinear optical applications. The vibrational contribution to the above properties has also been computed using the self-consistent field wave functions within the double harmonic oscillator approximation.

中文翻译：

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用于 NLO 器件制造的 (2E) 3-(4-ethoxyphenyl)-1-(3-bromophenyl) prop-2-en-1-one 的振动光谱表征、电子吸收、光学非线性计算和太赫兹研究

摘要 本研究突出了查尔酮衍生物 (2E) 3-(4-ethoxyphenyl)-1-(3-bromophenyl) prop-2-en-1-one (E3BC) 的关键结构-性质特征，以用于未来在非线性方面的应用。光学器件通过涉及实验和理论技术的双重方法。样品已通过 1H NMR、FT-IR、FT-Raman 和太赫兹光谱进行表征。实验结果得到了使用密度泛函理论的计算研究的支持。为了分析 1H NMR 光谱，化学位移的理论计算是通过 GIAO 方法完成的。根据内坐标的势能分布，已经对振动模式进行了完整的振动分配。通过太赫兹时域光谱检查了 0.2 和 1.8 THz 之间的低频振动模式。在甲醇溶液中记录紫外-可见光谱。电子单线态-单线态跃迁的能量、吸收波长和振子强度由时间相关密度泛函理论确定。计算出的 HOMO-LUMO 能隙很小，表明电荷转移发生在分子内，可用于非线性光学应用。分子的电荷密度分布和化学反应位点的信息已通过电子密度与分子静电势的映射获得。溴原子周围的 MEP 表面表现出双重性质。沿 C-Br 轴存在正静电势（σ 孔），而表面的其余部分为负。因此溴原子可以与亲核试剂和亲电试剂发生静电相互作用。对于其他原子，没有发现原子特定的影响。由超共轭相互作用和电荷离域引起的分子稳定性已使用自然键轨道分析进行了解释。该研究表明，分子内电荷转移（n → σ∗、n → π∗ 和 π → π∗）可以在分子中引起非线性，并验证了 E3BC 用作非线性光学活性材料的候选资格。为了理解分子的非线性光学活性，使用在 DFT 方法中实施的有限场方法来计算电子偶极矩、极化率、极化率的各向异性以及第一和第二超极化率。研究结果表明，标题分子的一级超极化率是尿素值的 139 倍。一阶超极化率的高值表明 E3BC 可以成为非线性光学应用中的潜在候选者。还使用双谐振子近似内的自洽场波函数计算了对上述特性的振动贡献。