Recent advances on chalcone-based photoinitiators of polymerization

Abstract

Photopolymerization is an active research field facing a revolution due to the recent availability of cheap, lightweight, compact and energy-saving light sources that constitutes light-emitting diodes (LEDs). With regards to the low light intensity delivered by these new irradiation setups, the demand for photoinitiating systems activable under low light intensity, in the visible range, and exhibiting a high reactivity even under air are actively researched.With aim at developing dyes fitting the above requirements while remaining relatively uncoloured, chalcones are one of those. In this review, an overview of the recent development concerning chalcone-based photoinitiating systems is reported. With aim at evidencing the crucial interest of this family of dyes, comparisons with benchmark photoinitiators will be presented.

Effects of the number and position of methoxy substituents on triphenylamine-based chalcone visible-light-absorbing photoinitiators

“…30–33 Conversely, monochalcones have structures comprising one chalcone moiety with asymmetric conjugation units. 29,34,35 In summary, bis-chalcones have been found to have higher molar extinction coefficients than monochalcones, but monochalcones offer greater flexibility regarding structure design. Thus, considering the desired photoreactivity relationship of the chalcone, the molecularly asymmetric configuration has considerable potential and should be systematically investigated.…”

“…A type II photoinitiator, chalcone, is currently considered to be a promising candidate because (1) the chalcone moiety can be easily prepared in high yield through a Claisen-Schmidt reaction, (2) chalcone's derivatives can be easily designed and modified, and (3) chalcone is present in numerous plants and offers biocompatibility. 29 Several types of visible-light-absorbing chalcones have been reported for photopolymerization. They have two main configurations, namely bis-chalcones (molecularly symmetric) and monochalcones (molecularly asymmetric) depending on whether both sides or one side of the structure has been modified.…”

“…They have two main configurations, namely bis-chalcones (molecularly symmetric) and monochalcones (molecularly asymmetric) depending on whether both sides or one side of the structure has been modified. 29,30 For example, bis-chalcones that include two chalcone moieties as a core within various unique conjugation units (such as heterocyclic aromatics, carbazole, phenylamine, and fused aromatics) on both sides were prepared. [30][31][32][33] Conversely, monochalcones have structures comprising one chalcone moiety with asymmetric conjugation units.…”

Recent advances on carbazole-based oxime esters as photoinitiators of polymerization

“…[35] Face to these considerations, polymerization of thick samples and even of resins containing fillers can be achieved. Reprinted with permission from Bonardi et al [35] Considering that the light penetration is the key parameter for achieving high monomer conversions, a wide range of structures have been examined ranging from truxene derivatives [36] to copper complexes, [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] carbazoles, [54][55][56][57][58][59][60][61][62][63][64][65] chalcones, [28,[66][67][68][69][70][71][72][73][74][75][76][77][78] zinc complexes, [79] acridones,…”

Chemical engineering around the 5,12-dihydroindolo[3,2-a]carbazole scaffold: Fine tuning of the optical properties of visible light photoinitiators of polymerization

“…[21][22][23][24][25][26][27][28][29] Face to these considerations, a second approach consists in developing new molecules totally disconnected from these historical structures. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] Considering that visible light photoinitiators of polymerization should exhibit a strong absorption over the visible range, long-living excited state lifetimes but also appropriate electrochemical properties in order to efficiently interact with the different additives introduced into the photocurable resins, structures commonly used in Organic Electronics are candidates of choice for photoinitiation. [49] In this field, carbazole is a popular structure in Organic Electronics and interest for this structure is supported by the easiness of chemical modification, its good photochemical and thermal stability, good electron-donating ability, high triplet energy level [50,51] and wide bandgap.…”