Penta-Methine Cyanine IRTs: Enabling NIR or Visible Photoinduced Polymerization of Acrylate and Thiol–Ene for Preparation of Polychromatic and Color-Changing Polymers

We first-ever investigated the near-infrared (NIR) cyanine dyes IRTs (IRT and IRTB), combined with iodonium salts (Iod), as new broad-absorbing photoinitiating systems (PISs), for initiating acrylate and thiol–ene photopolymerization under 808 nm laser and 630 and 450 nm light-emitting diode irradiation. The polymerization kinetics confirmed efficient initiation by IRTs/Iod systems under three light sources, and light plays a dominant role in driving the polymerization. The potential photolysis mechanisms of IRTs/Iod systems were explored. Furthermore, the acid–base-induced color-changing properties of IRT were investigated for the first time. In addition, based on the NIR absorption and color-changing properties of IRT, we successfully synthesized polychromatic polymers containing colored fillers and color-changing polymers using NIR photopolymerization. This research offers a feasible approach for developing broad-absorbing PISs and presents effective strategies for fabricating polychromatic polymers and color-changing polymers upon acid–base control using photopolymerization.