Photochemistry and photoinitiation activity of radical polymerization of 2‐substituted anthraquinone derivatives. III. Nanosecond laser flash photolysis study

Abstract

Plas Coch, Wrexham, Clwyd L11 2AW, U.K.; and 31nstituto de Ciencia y Tecnologia de Polimeros, C.S.I.C., c/]uan de la Cierva 3, 28006 Madrid, Spain SYNOPSIS A nanosecond laser Hash photolysis study was undertaken on a selected range of 2-substituted anthraquinone derivatives and the data are discussed in relation t o the photoactivities in industrial photopolymerization. All the compounds give rise to a triplet-triplet absorption t h a t is quenched by ground-state molecular oxygen. T h e transient half-lives range from 0.64 to 11.3 ps of which t h e 2-(l,l-dibromomethyl)anthraquinone exhibits t h e longest lifetime. In a reductive solvent, 2-propanol, hydrogen atom abstraction takes place with t h e compounds having t h e lowest-lying triplet 'hx* state, whereas those with a low-lying triplet 3 x x * state show mixed kinetics. In t h e latter case, a disproportionation reaction involving t h e semianthraquinone radical may be taking place, competing with t h e direct hydrogen atom abstraction reaction. In addition, investigation of t h e halogenated derivatives has indicated the possibility of t h e corresponding halo radicals being formed. In t h e presence of a tertiary amine, triethylamine, all anthraquinone derivatives show the formation of stable species related to either t h e exciplex or t h e radical ion pair. T h e extent of exciplex formation is more effective with compounds possessing a lowest-lying triplet 37r7r* excited state than those with a triplet 3 n~* excited state. T h e results from the nanosecond laser flash photolysis study show t h e differences in behavior toward hydrogen atom abstraction and electron transfer processes t h a t is dependent on t h e nature of the low-lying triplet state and the type of substituent present, i.e., electron-donating or electron-withdrawing.

Photochemistry and photopolymerisation of substituted 2-methylanthraquinones and novel 2-acryloxymethylanthraquinone in radiation curing

“…Therefore, this makes it less photochemically reactive. This fact is also in agreement with much of our previous reported studies [1][2][3][4][5][6][7][8]. We found that many 2-substituted anthraquinones exhibited a longest wavelength absorption maximum at between 330-360nm with a small and variable shift.…”

“…The photophysical and photochemical properties of anthraquinone derivatives has been one of the main areas of study in our research investigating the relationship and understanding between molecular structure, excited state properties and light stability and photochemical activity [1][2][3][4][5][6][7][8]. They have many applications in dye and pigmentbased, water and oil miscible, acrylated matrices.…”

“…Novel acryloxy and acrylamino and amido derivatives have been synthesised and produced significant enhancement in desirable photoinitiators for polymerisation and curing reactions whilst at the same time minimising unreacted diffusion in coatings systems. Direct halogenation has also given rise to high photochemical activity through photolysis giving aromatic and halogen free radicals through laser photolysis studies [6].…”

Other Properties of Solvents, Solutions, and Products Obtained From Solutions

“…These data come from the development of a standard for instrument calibration by NIST to improve the accuracy of measurements by application of nonlinear liquid standards. 4 Figure 11.2 shows the effect of polymer concentration on the viscosity of a solution of polyphenylene in N-methyl pyrilidinone. 5 Two regimes are clearly visible.…”

“…Work on anthraquinone derivatives, which are common photosensitizers, has shown that when photosensitizer is dissolved in isopropanol (hydrogen-donating solvent) the half-life of radicals is increased by a factor of seven compared to acetonitrile (a non-hydrogen-donating solvent). 4 This shows that the ability of a photosensitizer to act in this manner depends on the presence of a hydrogen donor (frequently the solvent). In studies on another group of photosensitizers  1,2-diketones, the solvent cyclohexane increased the absorption wavelength of the sensitizer in the UV range by more than 10 nm compared with solutions in ethanol and chloroform.…”