Visible-light-induced polymerization initiated by D-A dyes: towards rational design of efficient light-harvesting photoinitiators by regulation of excited states
The elongation of π-conjugation could efficiently enhance the photophysical performances or photochemical reactivties of organic molecules, which adapts to the requests of both designing fluorescent materials and organic photoinitiators (PIs). However, there is no work attempted to design organic PIs with large molar extinction coefficients and long π-conjugation lengths by using hybridized local and charge-transfer (HLCT) method, which is meaningful to obtain high-performance PIs with significant fluorescence/photoluminence properties. What's more, how to overcome the obstacles derived from the unbalance between high triplet concentrations and photoinitiation abilities of organic PIs seems to be crucial, while PI's design from a view of excited state were rarely reported for rational regulation strategy up to now, we thus introduced four chromophores with D-A structures designed by HLCT method, whose triplet states were confirmed by Ultra-fast absorption spectroscopy, into photopolymerzation, where LEDs in various wavelengths were utilized as the light sources in the present work. Noticeably, some of these dyes could furnish high monomer conversions and rapid photopolymerization rates, not only under the irradiation of 405 nm LED, but also long-wavelength light source at 660 nm, which have been confirmed by the photopolymerization kinetics and 3D printing technique. Here, the spin-orbit coupling (SOC) coefficients were carried out as well, to examine their effects on photoinitiation abilities of investigated molecules, which can be regarded as the first attempt to achieving light-harvesting PIs from excited state design. Finally, the corresponding photochemical mechanisms were investigated by steady state photolysis, fluorescence quenching experiments, particularly by frontier orbit energy and distributions to examine the interactions between these dyes with co-initiator/additives in details.
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