Tris‐benzo[cd]indole Cyanine Enables the NIR‐photosensitized Radical and Thiol‐ene Polymerizations at 940 nm

Abstract

A near‐infrared‐absorbing heptamethine (HM+) incorporating three bulky benzo[cd]indole heterocycles was designed to efficiently prevent self‐aggregation of the dye, which results in a strong enhancement of its photoinitiating reactivity as compared to a parent bis‐benzo[cd]indole heptamethine (HMCl+) used as a reference system. In this context, we highlight an efficient free‐radical NIR‐polymerization up to a 100% acrylates C=C bonds conversion even under air conditions. Such an important initiating performance was obtained by incorporating our NIR‐sensitizer into a three‐component system leading to its self‐regeneration. This original photoredox cycle was thoroughly investigated through the identification of each intermediary species using EPR spectroscopy.