Visible light‐emitting diode‐sensitive thioxanthone derivatives used in versatile photoinitiating systems for photopolymerizations

Abstract

Novel thioxanthone (TX) derivatives are used as versatile photoinitiators upon visible light-emitting diode (LED; e.g., 405, 425, and 450 nm) exposure. The mechanisms for the photochemical generation of reactive species (i.e., cations and free radicals) produced from photoinitiating systems based on the photoinitiator and an iodonium salt, tris(trimethylsilyl)silane, or an amine, were studied by UV-vis spectroscopy, fluorescence, cyclic voltammetry, steady-state photolysis, and electron spin resonance spin-trapping techniques. The reactive species are particularly efficient for cationic, free radical, hybrid, and thiol-ene photopolymerizations upon LED exposure. The optimized photoinitiating systems exhibit higher efficiency than those of reference systems (i.e., isopropyl TXbased photoinitiating systems), especially in the visible range. According to their beneficial features, these photoinitiating systems have considerable potential in photocuring applications.

Bicarbazole‐based oxalates as photoinitiating systems for photopolymerization under UV–Vis LEDs

“…As shown in Figure c, in the final monomer conversions ( t = 180 s) under different LED irradiation in the PI/MDEA‐containing systems, two PIs exhibited good performance in the near‐UV and visible range (365–475 nm). Thus, an improvement in long‐wavelength initiation ability was achieved compared with the commercial type II PI (such as isopropyl thioxanthone), which could not initiate FRP at irradiation wavelengths longer than 450 nm as reported in our previous work (Figure S9). When MO and DO were compared, the results showed that the time to achieve maximum heat release in DO was shorter than that in MO in the PI/MDEA‐containing formulation under all conditions.…”

“…1 H NMR and 13 C NMR spectra were recorded on a Bruker 400 M NMR spectrometer with CDCl 3 as the solvent and chemical shifts were reported in parts per million (ppm), downfield from the Me 4 Si resonance, which was used as the internal standard. Mass spectra were recorded on a Micromass GCT and Micromass GCTTM . All related spectra were shown in Data S1.…”

“…The cyclic voltammetry experiments (using a computer‐controlled Radiometer Voltalab 6 potentiostat with a three‐electrode single‐compartment cell; an Ag/AgNO 3 (0.1 M AgNO 3 in ACN) electrode used as a reference, Platinum electrode acts as working electrode and platinum wire acts as opposite electrode) were performed at 300 K, in N 2 ‐degassed ACN with a constant concentration (0.1 M) of n‐Bu 4 NBF 4 …”

Donor–acceptor–donor structured thioxanthone derivatives as visible photoinitiators

“…The design of these onecomponent photoinitiators was based on the functionalisation of thioxanthone with a coinitiator moiety (hydrogen donor). Wu et al 21…”

D‐π‐a‐type oxime sulfonate photoacid generators for cationic polymerization under UV–visible LED irradiation

“…Now, the commercial PAGs exhibit weak spectral sensitivity at long wavelengths ( λ abs > 320 nm), which limit their applications of new light sources, for example, light‐emitting diodes (LEDs) . PAGs have been adapted to operate under LED irradiation, especially near‐UV/visible LEDs . These eco‐friendly light sources have the advantages of low cost, absence of harmful ultraviolet light, high efficiency, and so on …”