Highly conjugated isoindigo and quinoxaline dyes as sunlight photosensitizers for onium salt‐photoinitiated cationic polymerization of epoxy resins
Bahar Tosun Ercan, Sirin Siyahjani Gültekin, Tamer Yeşil, Haluk Dinçalp, Sermet Koyuncu, Yusuf Yağcı, Ceylan Zafer
Abstract
Abstract In this study, photoinitiated cationic polymerization of epoxy resins by photoinduced electron transfer reactions using four new chromophoric dyes, namely (3 E )‐1,1′‐bis(2‐ethylhexyl)‐6,6′‐dipyren‐1‐yl‐3,3′‐biindole‐2,2′(1 H ,1′ H )‐dione (ISOIV), (3′ E )‐1,1′′′‐diethyl‐1′,1′′‐bis(2‐ethylhexyl)‐1 H ,1′′′ H ‐5,6′:3′,3′′:6′′,5′′′‐quaterindole‐2′,2′′(1′ H ,1′′ H )‐dione (ISOV), (3 E )‐6,6′‐bis(9‐ethyl‐9 H ‐carbazole‐3‐yl)‐1‐[(2 R )‐2‐ethylhexyl]‐1′‐[(2 S )‐2‐ethylhexyl]‐3,3′‐biindole‐2,2′(1 H ,1′H)‐dione (ISOVIII) and 3,3′‐(6‐bromokinoksalin‐2,3‐diyl)bis(9‐ethyl‐9 H ‐carbazole) (TPDC6), and diphenyliodonium hexafluorophosphate (Ph 2 I + PF 6 − ; DPI) under sunlight is reported. Upon irradiation, photoexcited dye forms an exciplex with DPI. Electron transfer reactions within the exciplex result in the formation of ionic species capable of initiating ring‐opening polymerization of an epoxy resin. It is shown that among the investigated dyes, ISOVIII and TPDC6 exhibited higher initiation efficiency in accordance with their stronger electron‐donating nature due to the presence of carbazole groups. © 2021 Society of Industrial Chemistry.