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Several 2‐phenylamino‐1,4‐naphthoquinone‐based dyes and two related benzo[2,3‐b]–phenazines were synthesised and characterised by proton nuclear magnetic resonance spectroscopy and electron ionisation mass spectrometry. The electrochemical and spectral properties of these compounds were investigated. The synthesised dyes were found to be capable photosensitisers for radical (reducible/oxidisable) and cationic polymerisations, respectively. In radical polymerization, better results in the oxidisable process were achieved.

Photoredox pairs consisting of 1,4‐naphthoquinone dyes and commercially available hydrogen donors (2‐mercaptobenzoxazole, 2‐mercaptobenzothiazole, 2‐mercaptobenzimidazole and 2,5‐dimercapto‐1,3,4‐thiadiazole) are found to be effective initiator systems for the radical polymerisation of trimethylolpropane triacrylate under visible light. The efficiency of these initiator systems is discussed in terms of the free energy change for the electron transfer process from the dye to the hydrogen donor. The results show that the photoinitiation ability of tested photoredox pairs depends on the structure of both the dye and the hydrogen donor.

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