Máximo-Canadas Matheus, Borges Itamar
Departamento de Química, Instituto Militar de Engenharia (IME), Praça General Tibúrcio, 80, Rio de Janeiro, RJ, 22290-270, Brazil.
J Mol Model. 2024 Apr 2;30(5):120. doi: 10.1007/s00894-024-05917-0.
Push-pull compounds are model systems and have numerous applications. By changing their substituents, properties are modified and new molecules for different applications can be designed. The work investigates the gas-phase electronic absorption spectra of 15 derivatives of push-pull para-nitroaniline (pNA). This molecule has applications in pharmaceuticals, azo dyes, corrosion inhibitors, and optoelectronics. Both electron-donor and electron-withdrawing groups were investigated. Employing machine learning-derived Hammett's constants σ, σ, σ, and σ, correlations between substituents and electronic properties were obtained. Overall, the σ constants presented the best correlation with HOMO and LUMO energies, whereas the σ constants best agreed with the transition energy of the first band and HOMO-LUMO energy gap. Electron-donors, which have lower σ values, redshift the absorption spectrum and reduce the HOMO-LUMO energy gap. Conversely, electron-withdrawing groups (higher σ's) blueshift the spectrum and increase the energy gap. The second band maximum energies, studied here for the first time, showed no correlation with σ but tended to increase with σ. A comprehensive charge transfer (CT) analysis of the main transition of all systems was also carried out. We found that donors (lower σ's) slightly enhance the CT character of the unsubstituted pNA, whereas acceptors (higher σ's) decrease it, leading to increased local excitations within the aromatic ring. The overall CT variation is not large, except for pNA-SOH, which considerably decreases the total CT value. We found that the strong electron donors pNA-OH, pNA-OCH, and pNA-NH, which have the smallest HOMO-LUMO energy gaps and lowest σ's, have potential for optoelectronic applications. The results show that none of the studied molecules is fluorescent in the gas phase. However, pNA-NH and pNA-COOH in cyclohexane and water reveal fluorescence upon solvation.
We investigated theoretically employing the second-order algebraic diagrammatic construction (ADC(2)) ab initio wave function and time-dependent density functional theory (TDDFT) the gas-phase electronic absorption spectra of 15 derivatives of p-nitroaniline (pNA). The investigated substituents include both electron-donor (CH, CCH, CH, NH, OCH, and OH,) and electron-withdrawing (Br, CCl, CF, Cl, CN, COOH, F, NO, and SOH) substituents.
推挽化合物是模型体系，有众多应用。通过改变其取代基，可以改变性质并设计出适用于不同应用的新分子。这项工作研究了推挽对硝基苯胺（pNA）的15种衍生物的气相电子吸收光谱。该分子在药物、偶氮染料、腐蚀抑制剂和光电子学中有应用。研究了供电子基团和吸电子基团。利用机器学习得出的哈米特常数σ、σ、σ和σ，获得了取代基与电子性质之间的相关性。总体而言，σ常数与最高占据分子轨道（HOMO）和最低未占分子轨道（LUMO）能量的相关性最佳，而σ常数与第一吸收带的跃迁能量和HOMO-LUMO能隙最为吻合。σ值较低的供电子基团使吸收光谱发生红移并减小HOMO-LUMO能隙。相反，吸电子基团（σ值较高）使光谱发生蓝移并增大能隙。本文首次研究的第二吸收带最大能量与σ无关，但倾向于随σ增大。还对所有体系的主要跃迁进行了全面的电荷转移（CT）分析。我们发现供体（σ值较低）略微增强了未取代pNA的CT特征，而受体（σ值较高）则降低了它，导致芳环内局部激发增加。除了pNA-SOH使总CT值大幅降低外，总体CT变化不大。我们发现具有最小HOMO-LUMO能隙和最低σ值的强供电子体pNA-OH、pNA-OCH和pNA-NH具有光电子应用潜力。结果表明，所研究的分子在气相中均无荧光。然而，环己烷和水中的pNA-NH和pNA-COOH在溶剂化后会发出荧光。
我们采用二阶代数图示构建法（ADC(2)）从头算波函数和含时密度泛函理论（TDDFT）对15种对硝基苯胺（pNA）衍生物的气相电子吸收光谱进行了理论研究。所研究的取代基包括供电子基团（CH、CCH、CH、NH、OCH和OH）和吸电子基团（Br、CCl、CF、Cl、CN、COOH）。
