Determining the excited‐state substituent constants of meta‐substituent from 3,4'‐disubstituted stilbenes

In this paper, 61 samples of 3,4'‐disubstituted stilbenes and 18 samples of 3,3'‐disubstituted stilbenes were synthesized, and their UV data were measured in anhydrous ethanol. Based on the UV absorption energy (wavenumber) of 3,4'‐disubstituted stilbenes, the excited‐state substituent constants of meta‐substituent were determined by means of curve‐fitting. The availability of was confirmed by the good correlation with the UV absorption energy of 3,4'‐disubstituted stilbenes and 4,4'‐disubstituted stilbenes. Further, using the obtained constants and the correlation equation, we calculated the UV wavenumbers of 3,3'‐disubstituted stilbenes, and the calculated wavenumbers are in good agreement with the experimental values. These results verified that the excited‐state substituent constants of meta‐substituent are reliable parameter to scale the effect of meta‐substituent on the UV absorption energy. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of Excited-state Substituent Constant on the UV Spectra of 1,4-disubstituted Benzenes

构建激发态取代基参数与1,4-二取代苯的紫外吸收波数之间的模型,成功地关联80个1,4-二取代苯的紫外吸收波数,其方程的相关系数为0.9805,标准偏差仅为672.27 cm^-1．结果表明激发态取代基参数适用于1,4-二取代苯紫外吸收能量的研究．同时提供了研究芳香化合物的紫外吸收光谱的新方法,并有利于深入理解多取代共轭化合物的激发态物理化学性质中的取代基效应     

The substituent effect on the UV energy of 4,4′‐disubstituted benzylideneanilines

In this paper, 72 samples of disubstituted benzylideneanilines were all synthesized, and their UV data were measured in anhydrous ethanol. In the study on the UV energy of the titled compounds with single substituent changed, for the effect of the aniline substituent Y on the UV wavenumbers, its UV data can be correlated with a dual‐parameter equation; for the effect of benzylidene substituent X on the UV data, its UV energy can be correlated with a single‐parameter equation (Y is an electron‐withdrawing group and H) or a dual‐parameter equation (Y is an electron‐donating group). In the study on the UV energy of model compounds with double substituents changed, a correlation equation between the UV absorption wavenumbers and substituent constants and σ_p, was obtained. For 72 samples of 4,4′‐disubstituted benzylideneanilines, the correlation coefficient was 0.9876, and the standard deviation s was only 358.46 cm^–1. The equation can be used to predict well the UV energy of BA derivatives. It was found that Δσ² is a better parameter than σ_XY to scale the substituent cross‐interaction effect on the UV wavenumbers of benzylideneanilines molecules. The results implied that the law of substituent effect on the UV energy of titled compounds is different from that of substituted stilbenes, and it is helpful to understand the effect of substituent effects on the chemical and physical properties of conjugated compounds with an imine bridging group (C = N) or a nonplanar parent. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of substituents and conjugated chain length on the UV spectra of α,ω‐di‐substituted phenyl polyenes

A series of α,ω‐di‐substituted phenyl polyenes, p‐X–Ph(CH = CH)_nPh–p‐Y (n = 1, 2, or 3) were synthesized, and their ultraviolet (UV) absorption maximum wavelength were determined. The correlation between molecular structure and the maximum wavelength energy (wavenumber/cm^?1) was carried out. The results show that the maximum wavelength energy of the title compounds is mainly affected by both substituent excited‐state parameters and maximum wavelength energy of the parent molecule. However, the two influence factors are not independent, and the action of substituent is governed by the parent molecular absorption energy. In the case of the compounds containing NO₂ or NH₂ groups, the influence of interaction of polarity parameters on the maximum wavelength energy must also be considered. In addition, the exploration was also made for the quantifying correlation of UV absorption maximum wavelength energy with the conjugated polarizability potential CPP replacing the parent molecular absorption energy. And the results indicate that the equation with CPP parameters is more accurate and convenient. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of substituent on the UV–Vis spectra: an extension from disubstituted to multi‐substituted benzylideneanilines

For studying the substituent effects on the ν_max of substituted benzylideneanilines (XBAYs) systematically, 12 samples of 3,3′‐disubstituted XBAYs and 52 samples of multi‐substituted XBAYs were synthesized, and the substituent effects on their ν_max were investigated in this paper. A modified regression equation quantifying the ν_max of 4,4′/4,3′/3,4′/3,3′‐disubstituted and multi‐substituted XBAYs (shown as Eq. 3 ) was obtained. The results showed that the substituent effects on the ν_max of 3,3′‐substituted and multi‐substituted XBAYs became more complicated. In Eq. 3 , the contributions of the meta‐parameters to the ν_max of XBAYs were different from those of the corresponding para‐parameters. For the substituent cross‐interaction effects, there is no difference whatever the substituents are at meta‐position or para‐position. Compared with Eq. 1 , Eq. 3 obtained in this paper has a wider application and more accuracy in quantifying the ν_max of substituted XBAYs. Copyright © 2016 John Wiley & Sons, Ltd.     

An attempt of molecular design and synthesis of 3,4′/4,3′‐disubstituted benzylideneanilines with specified UV–Vis absorption maximum wavelength

Thirty‐one samples of 3,4′/4,3′‐disubstituted benzylideneanilines (XBAY) with specified UV–Vis absorption maximum wavelength (λ_max) were designed and synthesized by applying the equation (Eqn 1 ) which was abstracted from the UV–Vis absorption maximum wavelength energy (ν_max = 1/λ_max) of 4,4′‐disubstituted benzylideneanilines. Then, the UV–Vis data (λ_max) of the designed compounds were measured in anhydrous ethanol. The predicted UV–Vis data of designed compounds are in agreement with the experimental ones, in which the mean absolute error is 2.9 nm. The results show that Eqn 1 is applicative for the prediction of UV–Vis absorption λ_max values of both 4,4′‐disubstituted benzylideneanilines and 3,4′/4,3′‐disubstituted benzylideneanilines. For a same pair of groups (X and Y), one can at least get four disubstituted benzylideneaniline compounds which have different λ_max values. It perhaps provides a convenient method to design an optical material for benzylideneaniline compounds. Copyright © 2014 John Wiley & Sons, Ltd.     

Substituent effect on the UV spectra of p‐disubstituted compounds XPh(CHCHPh)nY (n = 0, 1, 2)

Three parameters, , and , are developed to express the substituent effect and the effect of the parent molecular structure of p‐disubstituted compounds XPh(CH?CHPh)_nY (n = 0, 1, 2). The investigated result shows a good correlation between the UV absorption wavenumbers (υ_max) and the three parameters for a diverse set of title compounds, and the correlation equation can be used to predict the UV absorption energy of compounds with the mentioned structure. This approach provides a new insight for the quantitative structure‐property relationship (QSPR) correlation of the UV absorption energy of p‐disubstituted homologues. Copyright © 2010 John Wiley & Sons, Ltd.     

Influence of the chloro substituent position on the triplet reactivity of benzophenone derivatives: a time‐resolved resonance Raman and density functional theory study

A nanosecond time‐resolved resonance Raman (ns‐TR³) spectroscopic investigation of the photoreduction reactions and ability of several chloro‐substituted benzophenone (Cl‐BP) triplets is described. The TR³ results show that the 3‐chlorobenzophenone (3‐Cl‐BP), 4‐chlorobenzophenone (4‐Cl‐BP) and 4,4′‐dichlorobenzophenone (4,4′‐dichloro‐BP) triplets exhibit similar hydrogen abstraction ability with the parent BP triplet. In 2‐propanol, the 3‐Cl‐, 4‐Cl‐ and 4,4′‐dichloro‐diphenylketyl (DPK) radicals were observed and they appear to react with dimethylketyl radicals at the para‐position to form a light absorption transient species. These transient species were characterized with TR³ spectra, and identified with the help of results from density functional theory calculations. In an acetontitrile/water (MeCN:H₂O) 1:1 mixed solvent, these DPK radicals were also observed but with slower formation rates. However, the 2‐Cl‐DPK radical was observed to form with a lower yield and a significantly slower formation rate than the other chloro‐substituted benzophenones examined here in 2‐propanol under the same experimental conditions. These results reveal that the 2‐chloro substituent reduces the hydrogen abstraction ability of the substituted BP triplet, which was not as expected based on the assumption that the electron‐withdrawing group could increase its photoreduction ability. This unusual ortho effect of the chlorine substitution is briefly discussed. Copyright © 2011 John Wiley & Sons, Ltd.