Highly conjugated isoindigo and quinoxaline dyes as sunlight photosensitizers for onium salt‐photoinitiated cationic polymerization of epoxy resins

Abstract

In this study, photoinitiated cationic polymerization of epoxy resins by photoinduced electron transfer reactions using four new chromophoric dyes, namely (3E)‐1,1′‐bis(2‐ethylhexyl)‐6,6′‐dipyren‐1‐yl‐3,3′‐biindole‐2,2′(1H,1′H)‐dione (ISOIV), (3′E)‐1,1′′′‐diethyl‐1′,1′′‐bis(2‐ethylhexyl)‐1H,1′′′H‐5,6′:3′,3′′:6′′,5′′′‐quaterindole‐2′,2′′(1′H,1′′H)‐dione (ISOV), (3E)‐6,6′‐bis(9‐ethyl‐9H‐carbazole‐3‐yl)‐1‐[(2R)‐2‐ethylhexyl]‐1′‐[(2S)‐2‐ethylhexyl]‐3,3′‐biindole‐2,2′(1H,1′H)‐dione (ISOVIII) and 3,3′‐(6‐bromokinoksalin‐2,3‐diyl)bis(9‐ethyl‐9H‐carbazole) (TPDC6), and diphenyliodonium hexafluorophosphate (Ph2I+PF6−; 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.

Recent Advances on Quinoxaline-Based Photoinitiators of Polymerization

“…All the previous photoinitiators detailed in this review and absorbing at long wavelengths have been designed with thiophene units. In 2021, Yagci and coworkers introduced carbazole units as peripheral groups for TPDC6 (See Figure 26) [239]. From the electrochemical viewpoint, carbazole and thiophene exhibit similar electron-donating properties, so an excellent electron-donating chromophore could be prepared with carbazoles.…”

“…This resource is also free and unlimited on Earth and can allow the polymerization process to be carried out in energy-saving conditions. In 2021, the first photosensitizer based on quinoxaline dyes (TPDC6) was proposed by Zafer and coworkers (See Figure 26) [239]. In this study, Sun was not directly used as the light source but as a sunlight solar simulator.…”

Recent advances on visible light bodipys and related difluoroborane structures-based photoinitiating systems

“…Search for efficient photoinitiating systems was not limited to purely organic compounds and metal complexes were also studied such as gold complexes [233] iridium complexes, [234][235][236][237][238][239][240][241][242] zinc complexes, [243] copper complexes, [244][245][246][247][248][249][250][251][252][253][254][255][256][257][258][259][260][261][262] gold complexes [233] or iron complexes. [246,263,264] Various structures have been examined as solar photoinitiators, [1,[3][4][5][6][7]140,169,[265][266][267] as water-soluble structures, [66,71,…”

Recent Advances in Visible Light Photoinitiating Systems Based on Flavonoids

“…For decades, a great deal of effort has been devoted to developing greener photopolymerization processes, consisting in the use of biosourced photoinitiators and/or biosourced monomers [27][28][29], the use of sunlight instead of artificial light to initiate the polymerization [30][31][32][33][34][35] or the development of water-soluble photoinitiating systems enabling to avoid the use of organic solvents [36][37][38][39]. In order to identify the appropriate scaffold for designing high-performance visible light photoinitiators, a wide range of structures have been screened over the years, as exemplified with diketopyrrolopyrroles [40], bodipy [41][42][43][44][45][46], perylenes [47], dithienophosphole derivatives [48], thiophenes [49], cyclohexanones [50][51][52], quinoxalines [53][54][55][56][57][58][59][60][61][62][63][64][65][66], glyoxylates [67], cyanines [68], benzylidene ketones [69][70]…”