Journal ArticleDOI
Probing the reactivity of photoinitiators for free radical polymerization: time-resolved infrared spectroscopic study of benzoyl radicals.
Christopher S. Colley,David C. Grills,Nicholas A. Besley,Steffen Jockusch,Pavel Matousek,Anthony W. Parker,Michael Towrie,Nicholas J. Turro,Peter Gill,Michael W. George +9 more
TLDR
The results support a mechanism in which the alpha-cleavage occurs from the triplet excited state that has a lifetime less than or equal to the singlet excited state.Abstract:
A series of substituted benzoyl radicals has been generated by laser flash photolysis of alpha-hydroxy ketones, alpha-amino ketones, and acyl and bis(acyl)phosphine oxides, all of which are used commercially as photoinitiators in free radical polymerizations. The benzoyl radicals have been studied by fast time-resolved infrared spectroscopy. The absolute rate constants for their reaction with n-butylacrylate, thiophenol, bromotrichloromethane and oxygen were measured in acetonitrile solution. The rate constants of benzoyl radical addition to n-butylacrylate range from 1.3 x 10(5) to 5.5 x 10(5) M(-1) s(-1) and are about 2 orders of magnitude lower than for the n-butylacrylate addition to the counterradicals that are produced by alpha-cleavage of the investigated ketones. Density functional theoretical calculations have been performed in order to rationalize the observed reactivities of the initiating radicals. Calculations of the phosphorus-centered radicals generated by photolysis of an acyl and bis(acyl)phosphine oxide suggest that P atom Mulliken spin populations are an indicator of the relative reactivities of the phosphorus-centered radicals. The alpha-cleavage of (2,4,6-trimethylbenzoyl)phosphine oxide was studied by picosecond pump-probe and nanosecond step-scan time-resolved infrared spectroscopy. The results support a mechanism in which the alpha-cleavage occurs from the triplet excited state that has a lifetime less than or equal to the singlet excited state.read more
Citations
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Journal ArticleDOI
Three-dimensional optical laser lithography beyond the diffraction limit
TL;DR: In this article, a review of approaches aiming at translating this success in optical microscopy to optical lithography is presented, and basic principles and limitations, possible depletion mechanisms and recent lithography experiments by various groups are summarized.
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Achieving λ/20 Resolution by One-Color Initiation and Deactivation of Polymerization
TL;DR: An approach to photolithography is introduced in which multiphoton absorption of pulsed 800-nanometer (nm) light is used to initiate cross-linking in a polymer photoresist and one-photon absorption of continuous-wave 800-nmLight is used simultaneously to deactivate the photopolymerization.
Journal ArticleDOI
The Materials Challenge in Diffraction-Unlimited Direct-Laser-Writing Optical Lithography
TL;DR: This communication presents a novel class of photoresist systems, an example of which is successfully applied to DLW, and argues and shows that commercially available photoinitiators and photoresists containing them are far from ideal for the purpose of STED-DLW.
Journal ArticleDOI
Acrylic-based resin with favorable properties for three-dimensional two-photon polymerization
Tommaso Baldacchini,Christopher N. LaFratta,Richard A. Farrer,Malvin C. Teich,Bahaa E. A. Saleh,Michael J. Naughton,John T. Fourkas +6 more
TL;DR: In this paper, an acrylic-based prepolymer resin that is ideally suited for the fabrication of three-dimensional structures with two-photon polymerization is described and characterized.
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Photochemical strategies for the synthesis of gold nanoparticles from Au(III) and Au(I) using photoinduced free radical generation.
TL;DR: A paradigm for the photochemical production of nanoparticles of gold and other metal ions is provided that highlights ten aspects that must be considered in order to design successful photochemical systems for nanoparticle generation.
References
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Reaction Mechanism of Monoacyl- and Bisacylphosphine Oxide Photoinitiators Studied by 31P-, 13C-, and 1H-CIDNP and ESR
TL;DR: In this paper, a modification of Kaptein's rules for the 13C-NMR-CIDNP spectra was used to investigate the formation and reaction of phosphorus-centered radicals obtained from phosphorus-containing photoinitiators.
Journal ArticleDOI
Photochemistry and Photophysics of α-Hydroxy Ketones
TL;DR: In this paper, the photochemistry and photophysics of a series of derivatives of 2-hydroxy-2-methyl-1-phenyl propanone, a model photoinitiator for free radical polymerization, were investigated.
Journal ArticleDOI
Phosphinoyl Radicals: Structure and Reactivity. A Laser Flash Photolysis and Time-Resolved ESR Investigation
TL;DR: The photochemistry of a series of bis(acyl)phosphine oxides and the rate constants of the reactions of their phosphorus radicals with n-butylacrylate, thiophenol, bromotrichloromethane, oxygen, and methyl viologen have been investigated by laser flash photolysis.
Journal ArticleDOI
On the photolysis of acylphosphine oxides: 1. laser flash photolysis studies with 2,4,6- trimethylbenzoyldiphenylphosphine oxide
TL;DR: In this paper, a transient spectrum with a maximum at about 330 nm detected at the end of a flash was ascribed to the diphenyl phosphonyl radical (Ph 2 P = 0 ).