Derivatives of 1,4‐naphthoquinone as visible‐light‐absorbing one‐component photoinitiators for radical polymerisation

Bifunctional visible‐light photoinitiators for free radical polymerisation based on a 1,4‐naphthoquinone skeleton were synthesised and characterised using proton nuclear magnetic resonance spectroscopy and chemical ionisation mass spectrometry. Their basic spectroscopic properties, such as absorption and low‐temperature phosphorescence spectra, and their red‐ox properties were also measured. These initiators contain an appropriate electron/hydrogen donor group in the skeleton and do not require an additional coinitiator for initiation. During irradiation they act both as a triplet photosensitiser and as a hydrogen/electron donor. The ability of each naphthoquinone to act as a photoinitiator strongly depends on its chemical structure. These studies suggest that initiator radicals are generated from the triplet state in an intermolecular electron/hydrogen transfer reaction.