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.

Naphthoylenebenzimidazolone dyes as one‐component photoinitiators

“…Indeed, in some papers NMP is used as coinitiator. The same situation was encountered in previous papers [18,19]. Therefore, we used NMP as a diluted component.…”

“…The redox potentials were measured by cyclic voltammetry using a AUTOLAB potentiostat (Ecochemie, The Netherlands) at a scan rate of 100 mV s −1 in N , N ‐dimethylformamide, as described elsewhere . Photochemical experiments were conducted according to the procedure described in our previous paper . Briefly, a xenon lamp (Optel ZX 450 W, Poland) equipped with a 490 ± 90 nm bandpass filter was used as a light source.…”

“…The yields quoted refer to compounds after recrystallisation. Photochemical experiments were conducted according to the procedure described in our previous paper [19]. Low-resolution electron impact ionisation mass spectrometric analysis was carried out on Autospec Premier instruments (Waters, USA).…”

“…In the last decade many papers have described the synthesis of initiators. Only thioxanthone [3][4][5][6][7][8][9], benzophenone [10][11][12][13][14][15][16], erythrosine B [17], and, more recently, naphthoquinone [18] and benz[cd]indol-2(1H)-one [19] linked with appropriate groups have been applied as chromophores to obtain one-component initiator systems. There are two different ways to create initiators sensitive to visible radiation.…”

“…Such initiators are both photosensitiser and coinitiator, and their excited state is responsible for the generation of initiating radicals (Scheme ). Only thioxanthone , benzophenone , erythrosine B , and, more recently, naphthoquinone and benz[ cd ]indol‐2(1 H )‐one linked with appropriate groups have been applied as chromophores to obtain one‐component initiator systems.…”