Coumarinacyl Anilinium Salt: A Versatile Visible and NIR Photoinitiator for Cationic and Step-Growth Polymerizations

Abstract

A coumarinacyl anilinium (CAA) salt, facilely synthesized via a one-pot reaction, is shown to be a versatile visible and NIR photoinitiator for cationic and step-growth polymerizations. CAA salt exhibits superior photoinitiation performance as compared to commercial iodonium salt in cationic polymerization. Upon visible-light irradiation, this salt undergoes hemolytic and heterolytic cleavage and subsequent electron transfer and hydrogen abstraction reactions, forming reactive species capable of initiating cationic polymerization of epoxides and vinyl monomers. After a short irradiation period, polymerization also proceeds in the dark due to the non-nucleophilic nature of the counteranion. NIR-induced polymerizations were successfully conducted based on upconversion photochemistry. CAA salt can also initiate step-growth polymerization of N-ethyl carbazole (NEC) by oxidation of the monomer by the photochemically formed anilium radical cations. Subsequent proton release and radical coupling reactions essentially yield polycarbazole. CAA salt, featuring straightforward synthesis and long-wavelength sensitivity as well as versatile photoinitiating performance, has great potential in various applications.

An overview of photopolymerization and its diverse applications

“…Currently, two distinct categories of PISs exist that can be used for NIR photopolymerization. The first category encompasses systems reliant on upconversion nanoparticles (UCNPs) [88, 98, 100–106], and the second category consists of systems reliant on NIR dyes [90–92, 94, 95, 107–112], predominantly cyanines.…”

“…In 2023, Yagci et al [104] synthesized a coumarinacyl anilinium salt that demonstrated the capability to initiate cationic polymerization of cyclohexene oxide and step‐growth polymerization of N ‐ethyl carbazole. This PI could not only initiate photopolymerization under irradiation with 365 and 405 nm LED sources but also formed a PIS with UCNPs to achieve NIR light‐induced polymerization under irradiation with a 980 nm laser (Figure 19).…”

Push–pull coumarin-based one-component iodonium photoinitiators for cationic nanocomposite 3D-VAT printing

“…46,47 These salts show activity not only in cationic polymerization, but also in free-radical polymerization. 48…”

“…46,47 These salts show activity not only in cationic polymerization, but also in free-radical polymerization. 48 The most active of the onium salts are halonium salts containing a hypervalent halide atom in their structure. 49 Along with the high reactivity of these compounds also goes high instability, severely limiting their applicability.…”

From Glow to Growth: Chemiluminescence Induced Cationic Polymerization Using Ferrocenium Salt

“…Therefore, it is highly desirable to explore alternative excitation sources to address the inherent limitations of traditional light sources. To this regard, lanthanide-doped upconverting nanoparticles (UCNPs), which are able to convert near-infrared (NIR) light to UV-vis light, have been investigated as internal illumination sources to trigger free radical, [10][11][12] ionic, [13][14][15] and click photopolymerizations, [16,17] as well as controlled/living photopolymerizations. [18,19] Organic upconversion materials, with higher upconverting efficiency and superior compatibility in resins than inorganic counterparts, have been successfully applied to volumetrical 3D printing to fabricate delicate 3D objects with low excited laser power and high printing accuracy.…”