The photo-induced cleavage of acylphosphine oxides

Abstract

By the use of chemically induced dynamic electron polarisation acylphosphine oxides have been shown to undergo the Type I fission reaction from their triplet states.

A Novel Approach for Measuring Absolute Rate Constants by Pulsed Electron Spin Resonance: Addition of Phosphinoyl and 2-Hydroxy-2-propyl Radicals to Several Alkenes,

“…Similar spectra were observed 48,74,79,87,[91][92][93] and analyzed earlier. 92,93 The spectrum is polarized in net absorption due to the triplet mechanism 45,[94][95][96][97][98] and shows a doublet of singlets due to the diphenylphosphinoyl radical 1a.…”

“…The observed phosphorus hyperfine coupling constant of a(P R ) ) 36.2 ( 0.1 mT agrees with literature values. 35,74,93,99 In addition, a weak broad absorptive singlet can be observed near the centerfield and assigned to the benzoyl radicals (1b), whose signal intensity relative to the corresponding phosphinoyl radical is much weaker than in the well-established TR CW ESR spectra 74,79,87,91,93 due to the different detection methods. The TR CW method depends mainly on the spin-lattice relaxation time T 1 , and the TR FT method depends mainly on the phase memory time T M , and therefore, the difference found can result from the different relaxation times of the two radicals as was shown earlier for other systems.…”

“…ylphosphine oxide (1), which is widely used as a photoinitiator for free radical polymerization, 20,83-85 undergoes fast R-cleavage from a triplet excited state to produce strongly spin-polarized diphenylphosphinoyl radicals (1a) and 2,4,6-trimethylbenzoyl (1b): [86][87][88][89][90] The ESE spectra recorded 80 ns after photolysis of 1 are presented in Figure 2a. Similar spectra were observed 48,74,79,87,[91][92][93] and analyzed earlier.…”

Electron Spin Resonance and Laser Flash Photolysis Study of Radical Addition to Vinyl Acrylate and Related Alkenes

“…Photolysis of acylphosphine oxide 1a (25 mM) in ethyl acetate produce, after laser excitation, a pair of acyl (1b) and phosphinoyl radicals (1c) as shown in eq 1 41,46 The TR-ESR spectrum produced by photolysis of 1a is presented in Figure 1a. Similar spectra were observed 43,[46][47][48][49] and analyzed earlier.…”

“…Photolysis of acylphosphine oxide 1a (25 mM) in ethyl acetate produce, after laser excitation, a pair of acyl (1b) and phosphinoyl radicals (1c) as shown in eq 1 41,46 The TR-ESR spectrum produced by photolysis of 1a is presented in Figure 1a. Similar spectra were observed 43,[46][47][48][49] and analyzed earlier. 41,48 The spectrum is in polarized net absorption due to the triplet mechanism and shows a broad absorptive singlet near the centerfield assigned to benzoyl radicals 1b and a doublet of multiplets (see inset in Figure 1) due to the phosphinoyl radical 1c (a(P R ) ) 36.26 mT, a(H o ) ) 0.086 mT, a(H m ) ) 0.072 mT, a(H p ) ) 0.079 mT).…”