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NIR‐Sensitized Activated Photoreaction between Cyanines and Oxime Esters: Free‐Radical Photopolymerization
Author(s) -
Pang Yulian,
Fan Shuheng,
Wang Qunying,
Oprych Dennis,
Feilen Alfred,
Reiner Knut,
Keil Dietmar,
Slominsky Yuriy L.,
Popov Sergey,
Zou Yingquan,
Strehmel Bernd
Publication year - 2020
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202004413
Subject(s) - chemistry , photochemistry , radical , photopolymer , moiety , photoinduced electron transfer , excited state , oxime , electron transfer , polymerization , organic chemistry , polymer , physics , nuclear physics
Cyanines comprising either a benzo[e]‐ or benzo[c,d]indolium core facilitate initiation of radical photopolymerization combined with high power NIR‐LED prototypes emitting at 805 nm, 860 nm, or 870 nm, while different oxime esters function as radical coinitiators. Radical photopolymerization followed an initiation mechanism based on the participation of excited states, requiring additional thermal energy to overcome an existing intrinsic activation barrier. Heat released by nonradiative deactivation of the sensitizer favored the system, even under conditions where a thermally activated photoinduced electron transfer controls the reaction protocol. The heat generated internally by the NIR sensitizer promotes generation of the initiating reactive radicals. Sensitizers with a barbiturate group at the meso‐position preferred to bleach directly, while sensitizers carrying a cyclopentene moiety unexpectedly initiated the photosensitized mechanism.