Towards new NIR dyes for free radical photopolymerization processes.

Haifaa Mokbel,Frédéric Dumur,Guillaume Noirbent,Jacques Lalevée,Didier Gigmes

doi:10.3762/bjoc.17.133

Abstract

The use of cheap and safe near-infrared (NIR) light is still the subject of intense research efforts but remains a huge challenge due to the associated low photon energy (wavelength from 0.78 to 2.5 µm). In this study, a series of 17 NIR dyes mainly based on a well-established cyanine scaffold is proposed. Remarkably, 11 of them were never synthesized before. Markedly, noncharged structures, negatively charged cyanine bearing Na+ as counter cation, and positively charged cyanines bearing (B(Ph)4−) or (I−) as counter anions were examined as promising NIR light photoinitiating systems. Excellent photoinitiating abilities were found for some reported dyes when used in combination with iodonium salt and amine. Markedly, photothermal effects with a huge heater behavior were also observed for different NIR dye structures. Interestingly, the synthesis of interpenetrating polymer networks (IPNs, e.g., for the polymerization of acrylate/epoxy monomer blends) can also be carried out upon NIR light with the proposed systems.

Highlights

Photopolymerization processes are well established due to the specific features and advantages
Dyes Ca and Cb differ from the other cyanines by the asymmetric substitution
The proposed NIR dye/iodonium combinations are able to generate free radicals and cationic species (Scheme 7 and Figure 4), and these two-component systems can be used for the preparation of interpenetrating polymer network (IPN) through the polymerization of acrylate/epoxy monomer blends (3,4-epoxycyclohexylmethyl-3,4epoxycyclohexane carboxylate from Allnex was used as benchmark epoxy monomer) [20]

Summary

Introduction

Photopolymerization processes are well established due to the specific features and advantages. Both photochemical and photothermal NIR approaches were proposed to initiate polymerization, e.g., for free-radical processes, interpenetrating polymer network (IPN) synthesis, or photopolyaddition reactions [3,4,6,7,8,9]. A large series of 17 NIR dyes mainly based on a well-established cyanine scaffold is proposed (Scheme 1).

Results

Conclusion