Photochemical Radical Pathways of a Methyl‐Substituted Thioxanthone Disulfide Photoinitiator Enabling Oxygen‐Tolerant Photopolymerization and In Situ Gold Nanocomposites

Abstract

ABSTRACT The photophysical and photochemical performance of a visible‐light‐active disulfide‐based photoinitiator, 4,4′‐disulfanediylbis(1‐methyl‐9H‐thioxanthen‐9‐one) [CH 3 ‐TX‐S‐] 2 , was investigated and photopolymerization of mono and diacrylate and simultaneous metal nanoparticle generation were reported. The photoinitiator exhibits strong absorption in the visible region with a molar absorptivity of ε = 14,450 L·mol −1 ·cm −1 at 380 nm, enabling efficient excitation under light irradiation. Steady‐state fluorescence measurements revealed a low fluorescence quantum yield ( Φ f = 0.018), indicating efficient intersystem crossing, which is further supported by phosphorescence emission recorded at 77 K with a lifetime of τ p = 63 ms. The triplet energy level was determined as E T = 264 kJ.mol −1 , confirming the suitability of the excited triplet state for radical generation and photochemical reduction processes. Real‐time FTIR study demonstrated rapid and efficient photopolymerization of diacrylate formulations, with double‐bond conversion percentage values reaching 60 within 600 s. Cyclic voltammetry measurements revealed an irreversible oxidation process ( E p,a ≈ 1.76 V) and, together with photophysical data, indicated a strongly reducing excited state, supporting its role in photoinduced electron transfer processes. In parallel, the photogenerated thiyl radicals act as strong photoreductants, enabling the in situ reduction of Au 3+ ions to metallic Au 0 and the formation of gold nanoparticles during the photopolymerization process.