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

Abstract

Several potential initiators based on benz[cd]indol‐2(1H)‐one dye have been synthesised and evaluated in the radical polymerisation of a system containing trimethylolpropane triacrylate under visible light. Absorption, fluorescence, and phosphorescence spectra and the electrochemical properties of these novel dyes were determined. Owing to the presence of an appropriate hydrogen donor group in their structure, these photoinitiators do not need an extra coinitiator to initiate the polymerisation process. During photopolymerisation they act both as a triplet sensitiser and as a hydrogen donor. The relationship between the polymerisation rate and the triplet‐excited‐state reduction potential suggests that initiating radicals are formed from the triplet state via hydrogen transfer. This mechanism is supported by density functional theory calculations. 8‐Bromo‐6‐[(2‐sulphanylethyl)sulphanyl]benzo[cd]indol‐2(1H)‐one and 8‐bromo‐6‐sulphanylbenz[cd]indol‐2(1H)‐one may be applied as visible‐light initiators of free radical polymerisation to obtain a low‐molecular‐weight polymer.