Journal
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY
Volume 419, Issue -, Pages -Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.jphotochem.2021.113451
Keywords
alpha-Hydroxyalkyl acetophenone; Hydroxyalkyl-derivatives; Polymerizable photoinitiators; Hyperconjugation; Energy transfer
Categories
Funding
- National Key Research and Development Program of China [2017YFB0307800]
- Natural Science Foundation of Jiangsu Province of China [BK20200188]
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The study demonstrates that introducing a two-methylene spacer can effectively increase the photocleavage rate, leading to the design of new high-efficiency and polymerizable photoinitiators.
Five ester derivatives from hydroxyalkyl of 2-hydroxy-2-methyl-1-phenyl propanone, one of the most successfully applied alpha-hydroxyalkyl acetophenone photoinitiators, are synthesized. From the spectroscopy results and theory calculation, it is proved that the much lower photocleavage rates of the directly linked unsaturated ester derivatives are due to that the strong electron withdrawing effect of carbonyl increase the bond strength between the benzoyl and quaternary carbon and the effective energy transfer from benzoyl to double bond because of the existence of p-sigma-pi hyperconjugation, which consequently decreased their initiating ability. Excitingly, simple introduction of two-methylene spacer between the carbonyl and alkoxyl can effectively block the hyperconjugation and significantly increase the photocleavage rate up to the same level of their mother commercial photoinitiator, which can open a gate for design of new high efficiency and polymerizable type I photoinitiators.
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