Reaction Mechanism of Monoacyl- and Bisacylphosphine Oxide Photoinitiators Studied by ³¹P-, ¹³C-, and ¹H-CIDNP and ESR

31P-NMR-CIDNP (CIDNP = chemically induced dynamic nuclear polarization) spectroscopy was applied for the first time to investigate the formation and reaction of phosphorus-centered radicals obtained from phosphorus-containing photoinitiators. 13C-NMR- and 1H-NMR-CIDNP and ESR spectroscopies were used as complementary experimental techniques for the elucidation of the photochemistry of these compounds. The large hyperfine coupling constants of the 31P-nucleus results in a violation of Kaptein's rules, which is the only observation of this kind in 13C-NMR-CIDNP spectra reported so far. Interpretation of the CIDNP spectra, using a modification of Kaptein's rules for the 13C-NMR- and 1H-NMR-CIDNP, consistently shows that all compounds investigated undergo a photoinduced cleavage of the carbonyl−phosphinoyl bond from a triplet state. The fate of the primary radicals is discussed, and it is unambiguously shown by trapping experiments that the novel bisacylphosphine oxide photoinitiators give four radicals in a stepwise process.首次将磷-31核磁共振-化学诱导动态核极化（31P-NMR-CIDNP，其中CIDNP为化学诱导动态核极化（chemically induced dynamic nuclear polarization）的缩写）光谱技术应用于探究含磷光引发剂所生成的磷中心自由基的形成与反应过程。采用13C核磁共振-化学诱导动态核极化（13C-NMR-CIDNP）、氢核磁共振-化学诱导动态核极化（1H-NMR-CIDNP）光谱技术与电子顺磁共振（ESR）波谱作为互补实验手段，以阐明此类化合物的光化学机制。磷-31原子核的超大超精细耦合常数违背了开普坦规则（Kaptein's rules），这是目前已报道的13C-NMR-CIDNP光谱中此类现象的唯一观测实例。通过对13C-NMR-CIDNP与1H-NMR-CIDNP修正开普坦规则后对CIDNP光谱进行解析，结果一致表明所有受试化合物均从三重态发生光诱导的羰基-膦酰键断裂。本文探讨了初级自由基的演化路径，并通过自由基捕获实验明确证实：新型双酰基膦氧化物光引发剂会通过分步过程生成四种自由基。