Bis(2‐amino‐5‐thienyl)Ketone as Oxygen Tolerant Sensitizer for Conventional Radical Photopolymerization

Abstract

Abstract Bis(2‐amino‐5‐thienyl)ketones ( TK s) operated as effective sensitizer in a multi‐component photoinitiating system for conventional radical photopolymerization. The distinct amino pattern (morpholino 1  versus diaryl moiety 2 ) followed an oxidative photoinduced electron transfer ( PET ) mechanism with the iodonium salt C1 and the sulfonium cation C2 . 2 performed well under air upon UV‐LED exposure at 395 nm. The TK s mostly reacted from the triplet state (T 1 ) with either C1 or C2 resulting in a cation radical with certain instability. This changes considering the radical anion studied by spectroelectrochemistry confirmed by reversibility. Electrochemical measurements and transient absorption experiments disfavor from a thermodynamic point of view a reductive mechanism of the T 1 with C3 . Long‐lived charge separated states discuss a new paradigm as a further alternative to form reactive intermediates even with C3 . 1 O 2 generation by 3 TK * operated as additional pathway to form the initiating ∼N─CH 2 • radical of C3 . The higher efficiency of photoinduced electron transfer ( PET ) with C1 explained the higher network density of the crosslinked material. The subsequent [4+2] cycloaddition of 1 O 2 to the thiophene moiety led to a mass increase of 32 m z of either 1 or 2 , which led to depletion of inhibiting 3 O 2 . This additionally explains the unexpected, good oxygen tolerance. Furthermore, TK 2a showed no significant cytotoxic response explaining its future potential for biocompatible applications.