Abstract

The spectral-luminescent properties of the charged (anionic and cationic) forms of three biologically active substituted benzaldehydes, namely, o-anisaldehyde (2-methoxybenzaldehyde), syringaldehyde (3,5-dimethoxy-4-hydroxybenzaldehyde), and vanillin (3-methoxy-4-hydroxybenzaldehyde), are studied by quantum-chemical methods. Calculations show that the S₁ state of the charged forms of the studied molecules, in contrast to the neutral forms, is of the ππ* type, and its localization is similar to the localization of the S₂ (ππ*) state of the neutral molecules (anisaldehyde and vanillin) or of the S₃ (ππ*) state of syringaldehyde. According to the calculation results, the spectral range of 240–420 nm contains no new absorption bands corresponding to electronic transitions differing in nature and localization from the electronic transition of the neutral molecules. The calculated fluorescence characteristics of the charged forms of the studied molecules show that the radiative decay rate of the charged forms is considerably higher than that of the neutral forms, which is related to the different orbital nature of the S₁ state in the neutral and charged forms. Analysis of the calculated and experimental data on the fluorescence of the studied substituted benzaldehydes in alcohol solutions reveals that the fluorescence at 410 nm belongs to the cationic forms. Vanillin and syringaldehyde may also exhibit weak fluorescence of their anionic forms.

中文翻译：

---

某些取代的苯甲醛的带电形式的光谱发光性质

摘要

三种生物活性取代的苯甲醛的带电（阴离子和阳离子）形式的光谱发光性质，即邻茴香醛（2-甲氧基苯甲醛），丁香醛（3,5-二甲氧基-4-羟基苯甲醛）和香兰素（3-甲氧基-4-羟基苯甲醛），是通过量子化学方法研究的。计算表明，与中性形式相比，所研究分子的带电形式的S ₁状态为ππ*型，并且其位置类似于中性状态的S ₂（ππ*）状态的位置。分子（茴香醛和香兰素）或S ₃丁醛的（ππ*）状态。根据计算结果，在240-420 nm的光谱范围内没有新的吸收带，这些吸收带与中性分子的电子跃迁的性质和位置不同。计算得出的带电形式的分子的荧光特性表明，带电形式的辐射衰减速率明显高于中性形式，这与S ₁的不同轨道性质有关。以中性和带电形式陈述。对所研究的取代苯甲醛在醇溶液中的荧光的计算和实验数据的分析表明，在410 nm处的荧光属于阳离子形式。香兰素和丁香醛也可能显示出其阴离子形式的弱荧光。