Navickas Marius, Skliutas Edvinas, Kölbel Joseph, Fernández-Terán Ricardo J, Malinauskas Mangirdas, Vengris Mikas
Laser Research Centre, Vilnius University, Vilnius, Saulėtekio ave. 10, LT-10223, Lithuania.
Department of Physical Chemistry, University of Geneva, CH-1205 Geneva, Switzerland.
Phys Chem Chem Phys. 2025 Sep 12. doi: 10.1039/d5cp01612f.
Acylphosphine oxide photoinitiators, such as phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), are widely used as sensitisers in UV polymerisation applications due to their favourable properties for UV lithography. However, the underlying photophysical and photochemical mechanisms that govern their performance remain poorly understood. In this study, we systematically investigate these compounds using steady-state and time-resolved fluorescence, as well as electronic and infrared transient absorption spectroscopic techniques. The results show that the lowest electronic excitation of both BAPO and TPO leads to a rapid intersystem crossing (ISC) into the hot triplet manifold-which rapidly generates radicals, further undergoing relaxation and leading to a slower rate of radical formation from the cold triplet manifold. ISC is faster in TPO compared to BAPO, which exhibits more complex dynamics. In addition, time-resolved infrared data reveal that both sensitisers generate radicals (by α-cleavage) on a time scale similar to that of ISC, suggesting that the hot triplet state is very short-lived. Finally, nanosecond-to-microsecond electronic TA spectroscopy revealed multi-stage relaxation of the radicals with the formation of TPO photoproducts remaining detectable on microsecond time scales.
酰基氧化膦光引发剂，如苯基双(2,4,6-三甲基苯甲酰基)氧化膦(BAPO)和二苯基(2,4,6-三甲基苯甲酰基)氧化膦(TPO)，由于其在紫外光刻方面具有良好的性能，在紫外光聚合应用中被广泛用作敏化剂。然而，控制其性能的潜在光物理和光化学机制仍知之甚少。在本研究中，我们使用稳态和时间分辨荧光以及电子和红外瞬态吸收光谱技术对这些化合物进行了系统研究。结果表明，BAPO和TPO的最低电子激发都导致快速的系间窜越(ISC)进入热三重态流形，热三重态迅速产生自由基，进一步弛豫并导致从冷三重态流形形成自由基的速率较慢。与表现出更复杂动力学的BAPO相比，TPO中的ISC更快。此外，时间分辨红外数据表明，两种敏化剂在与ISC相似的时间尺度上通过α-裂解产生自由基，这表明热三重态非常短暂。最后，纳秒到微秒的电子瞬态吸收光谱揭示了自由基的多阶段弛豫，TPO光产物的形成在微秒时间尺度上仍然可以检测到。
