Yong Du, J. Xue, Mingde Li
2010
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Abstract
The photochemistry and photophysics of benzophenone (BP) as well as its derivatives have been the subjects of many studies due to their importance for understanding the photosensitizer mechanisms of electron transfer and hydrogen abstraction in the lowest triplet electronic excited states. Benzoylpyridines (BPy) are similar to BP and may be employed as potential photosensitizers due to their better water solubility than BP and they are particularly interesting since they contain heteroaromatic ring(s) with the nitrogen atom able to appear at different positions in the molecule. The different positions of N-substituents within the aromatic rings can significantly change the photophysical properties and photochemical reactivity of the BPy nπ* triplet state. By studying 2-BPy, 3-BPy and 4-BPy (where the number represents the N atom position within the aromatic rings) in different solvents with steady-state and laser flash photolysis measurements, Favaro and coworkers found that the lifetimes and reactivity of the triplet states 3-BPy and 4-BPy are very similar to those of BP while they observed appreciable differences and an unusual photodegradation behavior for 2-BPy. The fast intramolecular photocyclisation reaction occurs for 2-BPy in solvents that have H-bonding ability, but the reaction mechanism(s) for this reaction appears quite complex and controversial.