A new compound, 1,3-dimethoxy xanthione (DXT), has been synthesized and its absorption (stationary and transient) and luminescence spectra have been measured in n-hexane and compared with xanthione (XT) spectra. The pronounced broadening of xanthione vibronic absorption band related to the electronic transition to the second singlet excited state has been observed. Distinctions between the spectra of xanthione and its methoxy derivatives are discussed. Quantum chemical calculations of these compounds in the ground and excited electronic states have been accomplished to clarify the nature of electronic spectra changes due to modification of xanthione by methoxy groups. Appearance of a new absorption band of DXT caused by symmetry changes has been discussed. Calculations of the second excited state structure of xanthione and its methoxy derivatives confirm noticeable charge transfer (about 0.1 of the charge of an electron) from the methoxy group to thiocarbonyl group. Fitting of the transient spectra of XT and DXT has been fulfilled and the time constants of internal conversion S₂→S₁$S_2\to S_1$ and intersystem crossing S₁→T₁$S_1\to T_1$ have been determined. A considerable difference between the time constants of internal conversion S₂→S₁$S_2\to S_1$ in XT and DXT is uncovered.

中文翻译：

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黄酮及其衍生物的激发态的电子结构和种群动力学

已经合成了一种新的化合物1,3-二甲氧基黄酮（DXT），并已在正己烷中测量了其吸收（固定和瞬态）和发光光谱，并将其与黄酮（XT）光谱进行了比较。已经观察到与电子跃迁到第二单线态激发态有关的黄酮酮振动吸收带明显变宽。讨论了黄酮及其甲氧基衍生物的光谱之间的区别。这些化合物在基态和激发电子状态下的量子化学计算已经完成，以阐明由于甲氧酮修饰黄酮引起的电子光谱变化的性质。讨论了由对称性变化引起的新的DXT吸收带的出现。黄嘌呤酮及其甲氧基衍生物的第二激发态结构的计算证实了从甲氧基到硫代羰基的显着电荷转移（约0.1个电子电荷）。XT和DXT瞬态光谱的拟合已完成，并且内部转换的时间常数S ₂ →S ₁${\mathrm{小号}}_{\mathrm{2个}}\to {\mathrm{小号}}_{\mathrm{1个}}$和系统间交叉S ₁ →T ₁${\mathrm{小号}}_{\mathrm{1个}}\to {Ť}_{\mathrm{1个}}$已经确定。内部转换的时间常数S ₂ →S ₁之间存在相当大的差异${\mathrm{小号}}_{\mathrm{2个}}\to {\mathrm{小号}}_{\mathrm{1个}}$ 在XT和DXT中被发现。