Computational study of linear and nonlinear optical properties of substituted thiophene imino dyes using long-range corrected hybrid DFT methods

The molecular structures, linear and nonlinear optical properties of a series constituted by four R-substituted thiophene imino dyes, namely A(R?=?SO₂Me), B(R?=?SO₂Ph), C(R?=?NO₂), and D(R?=?C₂(CN)₃) were analysed using CAM-B3LYP, ωB97XD and LC-ωPBE hybrid DFT functionals in combination of the 6-311++G(d,p) standard basis set. The dipole moments, polarisabilities, HOMO-LUMO energy gaps, maximum absorption wavelengths and first hyperpolarisabilities were calculated in the gas phase and the obtained results are in good agreement with experimental NLO activity order A?<?B?<?C. Compared to synthesised dyes A-C, the designed dye D presents a longer maximum absorption wavelength and a lower HOMO-LUMO gap because of the appreciable stabilisation of its LUMO energy. These results were confirmed by the calculation of the total second-order stabilisation energy E⁽²⁾ defined in the context of the NBO population analysis. Consequently, dye D is predicted to exhibit a higher first hyperpolarisability in comparison with dyes A-C. This result can be justified by the enhanced intramolecular charge transfer in dye D due to the stronger electron-withdrawing ability and the cumulative action of the long π-conjugation of the tricyanovinyl moiety. The very high total hyperpolarisability (27 times greater than that of para-nitroaniline) of the designed dye D suggests its promising use in organic NLO devices.     

Adsorption of NH3 and NO2 molecules on C48B6N6 heterofullerene: A DFT study on electronic properties

Adsorption of NH₃ and NO₂ molecules on the external surface of C₄₈B₆N₆ heterofullerene is investigated using DFT method. Attachment of NH₃ and NO₂ on C₄₈B₆N₆ heterofullerenes are compared with the bare C₄₈B₆N₆ model optimized at the B3LYP/6-31G^? level. The high surface binding energies indicates that ammonia undergoes chemical adsorption and could be compatible with the long recovery time but C₄₈B₆N₆ should be good NO₂ sensors with quick response as well as short recovery time. Total (TDOS) and partial (PDOS) density of state calculations is also considered to elucidate the difference in the NH₃ and NO₂ gas detection mechanism of C₄₈B₆N₆. The overlap population density of state (OPDOS) indicated that the chemical adsorption is due to the overlap of atomic orbitals below the Fermi level. The calculated results suggest that the C₄₈B₆N₆ heterofullerene is a suitable sensor material for NO₂ and is an ideal material for elimination and filtering of ammonia.     

DFT-based study of the impact of transition metal coordination on the charge transport and nonlinear optical (NLO) properties of 2-{[5-(4-nitrophenyl)-1,3,4-thiadiazol-2-ylimino]methyl}phenol

Theoretical investigations of the impact of transition metal chelation on the electron/hole-transport and nonlinear optical (NLO) properties of 2-{[5-(4-nitrophenyl)-1,3,4-thiadiazol-2-ylimino]methyl}phenol (L) are reported herein. Calculations were carried out via density functional theory (DFT)-based methods, employing exchange–correlation functionals and basis sets of different qualities. Results have shown that free L is a moderate electron/hole-transporter, but that its Pd(II) and Pt(II) complexes are excellent hole- and electron-transport materials respectively, owing to their very small reorganisation energies and relatively large electronic coupling matrix elements or transfer integrals. These results indicate that the complexes are potentially suitable charge transport materials for the construction of organic light emitting diodes (OLEDs). Nevertheless, the results also revealed a higher NLO activity for L than its metal complexes. Interestingly, the first and second hyperpolarizabilities, along with some computed NLO properties of both L and its complexes are found to be remarkably higher than those of the prototypical push–pull molecule, para-nitroaniline. Accordingly, these compounds are potential candidates for the fabrication of optoelectronic and photonic devices for second- and third-order NLO applications. Summarily, metal chelation is found to enhance the charge transport properties in some cases, and to slightly diminish NLO response of L in all cases investigated.     

Does gold cluster promote or scavenge radicals? A controversy at DFT

Anticancer character of gold cluster has been indicated through its free radical scavenging properties. This is in contrast to its free radical promoting ability suggested by other workers. Here, we address this controversy by probing the stabilizing effects of Au₃ cluster on RO^• vs its impacts on RO–H bond dissociation enthalpy, at B3LYP/ LACVP+* level (R═H, methyl, ethyl, n‐propyl, i‐propyl, n‐butyl, t‐butyl, and phenyl). In the presence of Au₃ cluster, bond dissociation enthalpy of O–H bond and the spin density at the RO^• oxygen are reduced dramatically. These are clear evidences for both the Au₃ facilitation of the RO–H bond breakage and its scavenging of RO^• radical. Since O–Au anchoring bond is responsible for the interaction of Au₃ cluster and ROH (or RO^•), its nature was interpreted by means of the quantum theory of atoms in molecules and the natural bond orbital. The results indicate that O–Au bond is stronger and has more covalent character in RO^•–Au₃ than in ROH–Au₃. The interaction of Au₃ cluster with RO^• is 1.5 to 3 times more than that with ROH. As a result, gold cluster scavenging property appears more prominent than its free radical initiation activity.     

多巴胺DA分子的构象异构及其一水复合物的结构与性质研究

采用密度泛函B3LYP/6-31+G·方法对多巴胺DA的构象异构及其稳定性进行了研究. 结果表明,势能面上存在6种稳定构象和8种构象转换过渡态, 构象之间主要通过C1-O7 [二面角T1: H15O7C1C6], C2-O8 [二面角T2: H16O8C2C3]和C9-C10 [二面角T3: N11C10C9C5]单键旋转而相互转化. 频率及NBO分析表明, 分子内存在红移O...H-O及蓝移N...H-C两类氢键, 氢键中电子转移类型均为LP1(X)→σ·(H-Y)[X=O, N; Y=O, C], 二级稳定化能E(2)对稳定构象有3.6 kJ·mol-1～9.3 kJ·mol-1的稳定化贡献. 分子中的原子理论(AIM)分析表明, 构象中O...H-O及N...H-C键的电子密度ρ(r)和Laplacian量2ρ(r)分别在0.0094～0.0171和0.0307～0.0798之间. 采用极化连续模型(polarized continuum model, PCM)对体系进行了溶剂化效应计算, 结果表明, DA的构象转换主要在水相中进行. 应用静电势模型(electrostatic potential map, EPM)对构象的活性位点进行了预测, 并以此研究了多巴胺一水复合物的结构与性质.     

Density functional investigation of the electronic properties of B80 fullerene exposed to regioselective chemisorption of nucleophiles NH3, PH3 and AsH3

DFT calculations at B3LYP/6-31G(d,p) level are applied to investigate the effect of regioselective chemisorption of nucleophiles NH3, PH3 and AsH3 on the electronic properties of B80 fullerene based on computing CS and EFG parameters and natural charges. Three directions of approaching are considered, the frame site, endohedral and exohedral caps. Our results demonstrate CS and EFG tensors are sensitive to the positions of attached sites and that attachment of XH3 to B80 fullerene exerts not only a structural but also an electronic environment deformation to the cage. Natural charge analyses show about 0.4 e transfer from NH3 ligand and about 0.8 e transfer from PH3 and AsH3 ligands to the cage of B80 fullerene. Parallel to NQR parameters and natural charge analyses suggest that electronic density increases on the first neighbor of B1 in NH3–B80 models and increases on B1 and its first neighbors in PH3–B80 and AsH3–B80 models.     

NLO characteristics of D-π-A coumarin-thiophene bridged azo dyes by Z-scan and DFT methods

ABSTRACT

The structural, electronic, intramolecular charge transfer (ICT) and nonlinear optical (NLO) properties of the donor-π-acceptor (D-π-A) azo linked dyes bearing coumarin thiophene bridge with different acceptors were inspected by Z-scan and DFT methods. The dye 3a exhibits bathochromic absorption maxima (649 and 650?nm) in the near IR region in DMF and DMSO. The dye 3a holds low HOMO–LUMO gap elucidated by CV and DFT indicating strong ICT character. The thermal stability is high for 3a and it shows enhanced NLO property by Z-scan and DFT methods as predicted in both global and range-separated hybrid functionals. The molecular geometry was optimised using B3LYP/6-311?+?g(d,p). The ICT characteristics are correlated with NLO properties obtained by Z-scan and DFT techniques.