Photoinitiator photophysical properties

TABLE 12.1 Photophysical Properties of Photoinitiators in Acetonitrile and Other Nonviscous Solvents"... 

Free and polymer-bound 2-benzyloxy-thioxanthone exhibit similar flash photolysis behaviour and the same photoreduction quantum yield in the presence of 2-(A, AT-diethylamino) ethanol. This clearly shows that the polymeric nature does not appear to affect photophysical properties of the thioxanthone moiety. The photoinitiated polymerization of MMA in benzene solution, using BOTX and poly(StX-co-St) in combination with 2-(MA -dieffiylamino) ethanol, indicates that the polymer-bound chromophore seems to operate in the same way and with similar efficiency as the free photoinitiator, at least in conditions of dilute chromophore concentration. 

Copolymers of 2-acryloyl-thioxanthone (TXA) with MMA [poly(TXA-co-MMA)] have also been prepared [47,48] and the photophysical properties as well as the free radical photoinitiation in the polymerization of MMA studied [49,50]. 

Transition metal-carbonyl-diimine complexes [Ru(E)(E ) (CO)2(a-diimine)] (E, E = halide, alkyl, benzyl, metal fragment a-diimine = 1, 4-diazabutadiene or 2,2 -bipyridine) are widely studied for their unconventional photochemical, photophysical, and electrochemical properties. These molecules have a great potential as luminophores, photosensitizers, and photoinitiators of radical reactions and represent a challenge to the understanding of excited-state dynamics. The near-UV/visible electronic spectroscopy of [Rn(X)(Me)(CO)2(/Pr-DAB)] (X = Cl or I iPr-DAB = A,A -di-isopropyl-l,4-diaza-l,3-butadiene) has been investigated throngh CASSCF/C ASPT2 and TD-DFT calculations on the model complexes [Ru(X)(Me)(CO)2(Me-DAB)] (X = Cl or I) (Table 2). 

In this chapter, we will focus on photosensitive systems that are used in free radical photopolymerization reactions. We will give the most exhaustive presentation of the commercially used or potentially interesting systems developed on a laboratory scale together with the characteristics of their excited-state properties. We will also show how modem time resolved laser spectroscopy techniques and quantum mechanical calculations allow to probe the photophysical/photochemical properties as well as the chemical reactivity of a given photoinitiating system. 

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