Dyes based on a 1,4‐naphthoquinone skeleton as new type II photoinitiators for radical polymerisation

Abstract

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.

Synthesis and application of dyes derived from benz[cd]indol‐2(1H)‐one as visible‐light‐absorbing polymerisation photoinitiators

“…Dyes 3 to 6 were synthesised in excellent yields (87-95%), and their chemical structures were verified by 1 H NMR, 13 C NMR, and MS (EI) (see the supporting information for further details). This procedure was repeated until TLC purity was obtained.…”

Dyes based on the 6,7‐dichloro‐5,8‐quinolinedione skeleton as new type II photoinitiators for radical polymerisation

“…Similar thermodynamic results were obtained for the systems consisting of naphthoquinone/phenazine dyes and hydrogen donors described in a previous paper . For all the systems studied, the values of Δ G el were negative and ranged from −74 to −169 kJ mol −1 .…”

“…Based on a comparison of these results with the data presented for naphthoquinone dyes , it is evident that better results were achieved for systems consisting of dyes based on the 5,8‐quinolinedione skeleton and hydrogen donor D2 . For the naphthoquinone analogues, the R p values were usually in the range 6–9 μmol s −1 , whereas for the tested dyes Ia to f these values are ca .…”

“…Slightly better results were also achieved for systems with 2‐mercaptobenzoxazole D1 . For phenazines, the previously described derivatives were found to be more efficient in photoredox pairs with D2 to D4 .…”

“…In previous papers [17,18], the synthesis and the electrochemical and spectral properties of dyes derived from 1,4-naphthoquinone were reported. It was demonstrated that these compounds are capable type II photoinitiators for the radical polymerisation of trimethylolpropane triacrylate (TMPTA).…”