Department of Chemistry, Yildiz Technical University , Davutpasa Campus, Istanbul 34210, Turkey.
J Org Chem. 2013 Sep 20;78(18):9161-5. doi: 10.1021/jo401386t. Epub 2013 Aug 28.
A photoinitiator for free-radical polymerization based on a thioxanthone chromophore containing two acetic acid functions was synthesized and characterized. Photophysical studies such as fluorescence, phosphorescence, and laser flash photolysis in addition to photopolymerization of acrylates were performed to elucidate the radical generation mechanism involving intramolecular electron transfer from the triplet state followed by decarboxylation. We found that the position of the acetic acid substituent is critical for the photoreactivity. In most solvents and acrylic monomers, if the acetic acid functionality is at the 1-position, the singlet excited states are deactivated rapidly before electron transfer can occur, resulting in negligible photoreactivity. The excited-state deactivation probably involves intramolecular H-bonding deactivation. The intramolecular H-bonding is disrupted by solvents that support intermolecular H-bonding, such as DMF and DMSO, leading to efficient intramolecular photoreaction.
基于含有两个乙酸官能团的噻吨酮发色团的自由基聚合光引发剂被合成并进行了表征。进行了光物理研究，如荧光、磷光和激光闪光光解，以及丙烯酸酯的光聚合，以阐明涉及从三重态进行分子内电子转移，然后进行脱羧的自由基生成机制。我们发现，乙酸取代基的位置对于光反应性至关重要。在大多数溶剂和丙烯酸单体中，如果乙酸官能团位于 1 位，则在电子转移发生之前，单重激发态会迅速失活，导致光反应性可忽略不计。激发态失活可能涉及分子内氢键失活。分子内氢键被支持分子间氢键的溶剂破坏，例如 DMF 和 DMSO，从而导致有效的分子内光反应。
