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探明影响甲基红光谱性质的各种因素,有助于拓宽偶氮苯衍生物在有机光电器件中的应用。采用密度泛函理论和实验相结合的方法研究了溶液酸碱性和溶剂水对邻位甲基红水溶液光谱的影响。溶液pH从13.1逐渐降低至0.5,邻位甲基红水溶液的最大吸收波长从430 nm红移至520 nm。在不同酸碱条件下,主要有三种物种共存于甲基红水溶液中,它们分别是双质子化的甲基红o-H_2MR+(强酸性条件下),单质子化的甲基红oHMR(弱酸条件下)和碱性甲基红o-MR–(碱性条件下),通过密度泛函理论计算研究了三种不同形式的电子结构特征。采用含时密度泛函理论计算了甲基红偶极跃迁允许的最低激发能,分别采用连续介质模型和分子簇模型研究水溶剂对甲基红电子结构和光谱性质的影响。在酸性条件下,o-H_2MR+和o-HMR分子内氢键导致π共轭体系平面性增强,因而光谱红移。而在碱性条件下,溶剂对o-MR–的光谱有显著影响:极性o-HMR和o-MR–与水分子的偶极–偶极相互作用导致光谱进一步红移。
To explore various factors that affect the properties of methyl red spectroscopy, help to broaden the azobenzene derivatives in the application of organic optoelectronic devices. Density functional theory and experimental methods were used to study the influence of acidity and alkalinity of solution and the solvent water on the spectra of o-methyl red aqueous solution. The pH of the solution gradually decreased from 13.1 to 0.5. The maximum absorption wavelength of o-methyl red aqueous solution was red-shifted from 430 nm to 520 nm. Under the different acid-base conditions, there are mainly three species coexisting in methyl red aqueous solution, which are the double protonated methyl red o-H 2MR + (strong acidic conditions), the single protonated methyl red oHMR (weak acid conditions ) And basic methyl red o-MR- (basic conditions), by the density functional theory calculations of three different forms of electronic structure characteristics. The lowest allowable excitation energy of methyl red dipole transition was calculated by using time-dependent density functional theory. The effects of water solvent on the structure and spectral properties of methyl red were studied by continuum model and molecular cluster model respectively. Under acidic conditions, intramolecular hydrogen bonding between o-H 2MR + and o-HMR results in the enhancement of the planarity of π-conjugated system, resulting in a red-shifted spectrum. Under alkaline conditions, however, the solvent has a significant effect on the spectra of o-MR-: the dipole-dipole interaction of polar o-HMR and o-MR- with water molecules leads to a further red shift of the spectra.