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.