Photochemistry of quinoxaline derivatives and mechanism of the triplet state quenching by electron-poor alkenes

Light-Responsive Pyrazine-Based Systems: Probing Aromatic Diarylethene Photocyclization

“…It was found that an emerging absorption at 410 nm occurs upon laser flash excitation of 2, correlating very well with the quinoxaline intermediate triplet excited state. [42][43][44] This was in accordance with a monoexponential decay of this absorbance on a µs scale (Figure 7c; for more details see Section S6 in the SI). However, the photocyclization of the majority of conventional diarylethene photoswitches was shown to occur without intersystem crossing.…”

“…To better understand the processes governing the resistance of 2 to photocyclization in contrast to 1 and 3 , we monitored their behavior in the excited state by transient absorption spectroscopy upon laser flash excitation at 355 nm. It was found that an emerging absorption at 410 nm occurs upon laser flash excitation of 2 , correlating very well with the quinoxaline intermediate triplet excited state. − This was in accordance with a monoexponential decay of this absorbance on a microsecond scale (Figure c; for more details, see Section S6 in the SI). However, the photocyclization of the majority of conventional diarylethene photoswitches was shown to occur without intersystem crossing. , In addition, stabilization of the twisted intermolecular charge transfer (TICT) states can be a possible explanation for inhibited photocyclization .…”

“…Photocyclization is revealed by the appearance of the new absorption bands at 400 and 643 nm, which disappear even in the dark after 15 min. (c) Decay of the absorption at 290 nm of 2 after laser excitation at 355 nm, which along with the decay at 410 nm (presented in Section S6 in the SI) confirms the absence of photocyclization as a result of the excitation to a triplet state typical for quinoxaline systems. − (d) UV–vis spectra of DAE 3 in toluene at ambient temperature upon photocyclization by illumination at 350 nm (Rayonet RMR-600, eight lamps of 8 W). The inset represents the evolution of the absorption at 550 nm over time until the PSS is reached.…”

“…10 Moreover, the loss of aromaticity upon cyclization, as evidenced by the NICS(1) πZZ calculations (Figure 3 along with the decay at 410 nm (presented in Section S6 in the SI) confirms absence of photocyclization as a result of the excitation to a triplet state typical for quinoxaline systems. [42][43][44] (d) UV-Vis spectra of DAE 3 in toluene at ambient temperature upon photocyclization by illumination at 350 nm (Rayonet RMR600, 8 lamps of 8 W). Inset represents the evolution of the absorption at 550 nm over time until the PSS is reached.…”

Photoinduced Electron and Hydrogen Transfer Reactions of Thioxanthone with Amines, Phenols and Alcohols

“…并且与以前研究的胺类、酚类、醇类与 吨酮(XT)、 芴酮(FL)三重态反应的结果 [20] 进行了 比较. (GDB59)将光信号转换 为电信号并放大后, 用数字示波器(400MHz,TDS380 型, 美国 Tektronix 公司)记录存储瞬态衰减曲线 [21][22] . [6] 和 Corrales [24]…”