Abstract
Polymerization photoinitiators that can be activated under low light intensity and in the visible range are being pursued by both the academic and industrial communities. To efficiently harvest light and initiate a polymerization process, dyes with high molar extinction coefficients in the visible range are ideal candidates. In this field, Donor-acceptor Stenhouse Adducts (DASA) which belong to a class of recently discovered organic photochromic molecules still lack practical applications. In this work, a series of DASA-based dyes are proposed as photoinitiators for the free radical polymerization of (meth)acrylates upon exposure to a near infrared light (laser diode at 785 nm).
Highlights
Push-pull dyes composed of an electron donor connected to an electron acceptor by means of a conjugated or a non-conjugated spacer have become a thriving research area, impelled by their potential applications ranging from non-linear optical (NLO) applications [1], organic photovoltaics (OPVs) [2], organic field effect transistors (OFETs) [3], photopolymerization [4,5,6,7,8,9,10,11] or photocatalytic degradation of dyes [12]
Considering that piperidine can initiate an undesired nucleophilic addition on the push-pull dyes subsequent to their syntheses, pyridine was selected as the base to catalyze the Knoevenagel reaction
For DASA1, DASA2 and DASA7, fast and efficient polymerization processes are observed despite a rather long lag time of ~200 s ascribed to the oxygen inhibition
Summary
Push-pull dyes composed of an electron donor connected to an electron acceptor by means of a conjugated or a non-conjugated spacer have become a thriving research area, impelled by their potential applications ranging from non-linear optical (NLO) applications [1], organic photovoltaics (OPVs) [2], organic field effect transistors (OFETs) [3], photopolymerization [4,5,6,7,8,9,10,11] or photocatalytic degradation of dyes [12]. The color change is reversible and can be triggered by exciting the molecules at a second irradiation wavelength carefully selected In this field, the most popular photoswitches include azobenzenes [15], diarylethenes [16], dihydroazulenes [17] or spiropyrans [18]. DASA are chromophores well-known to exhibit high molar extinction coefficients [45,46,47,48], so their content in the photocurable resin can be drastically reduced, addressing the photoinitiator extractability issue [48,49,50,51,52] Facing these different considerations, in this work, a series of twenty-four push-pull adducts.
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