Reactions of Triplet Decafluorobenzophenone with Alkenes. A Laser Flash Photolysis Study

Abstract

Rate constants for the reactions of triplet decafluorobenzophenone (3DFB) with 30 alkenes have been measured, with values in the range 107−109 L mol-1 s-1. The rate constant increases upon substituting electron-donating groups on the double bond, whereas it decreases upon substituting electron-withdrawing groups. For cyclohexene and 2-butene, the rate constant increases with increasing methyl substitution at the double bond, suggesting that steric effects play a minor role in the reaction. Further, there is a linear correlation between log k r (k r = the second-order rate constant of the reaction of 3DFB and alkene) and the ionization potential of the alkene. The extent of hydrogen abstraction was determined by measuring the yield of the ketyl radical. Quantum yields for ketyl radical formation, ΦK, increase with the ionization potential and the number of activated hydrogens, nH, on the alkene. The absolute values of ΦK and a linear correlation between ΦK/nH and ionization potential suggest that hydrogen abstraction is preceded by complex formation.

On the interaction mechanism of radical photoinitiators with monomers

“…7 Just as n* character ketones can abstract an hydrogen atom from alkanes or alcohol, the same process can take place with the allylic hydrogen of an alkene. 8 Thus, in the case of an alkene exhibiting an allylic hydrogen, the abstraction reaction can either be a one-step reaction or originate from a precursor exciplex. The predominance of one way over the other depends on the reduction potential and the triplet energy of the ketones with a given alkene.…”

Versatile Approach to Building Dynamic Covalent Polymer Networks by Stimulating the Dormant Groups

“…34−41 Under UV radiation, BP exhibits preferential reactivity toward unreactive C−H bonds, which results in the abstraction of hydrogen atoms from adjacent aliphatic chains to form aliphatic radicals and diarylsemipinacol (DASP) radicals. 42,43 The combination of these two radicals can result in the formation of covalent bonds. Since most polymers have C−H groups, BP has been used as a generally effective chemical for modifying the surfaces of polymers.…”

“…Benzophenone (BP), a commonly used photoinitiator and photografting agent, has received a great deal of attention due to its low cost, high photochemical activity, and wide applicability in polymeric materials. − Under UV radiation, BP exhibits preferential reactivity toward unreactive C–H bonds, which results in the abstraction of hydrogen atoms from adjacent aliphatic chains to form aliphatic radicals and diarylsemipinacol (DASP) radicals. , The combination of these two radicals can result in the formation of covalent bonds. Since most polymers have C–H groups, BP has been used as a generally effective chemical for modifying the surfaces of polymers.…”

Influence of the chloro substituent position on the triplet reactivity of benzophenone derivatives: a time‐resolved resonance Raman and density functional theory study

“…The reaction details and properties of the excited states of BP and its derivatives have been revealed extensively through the broad application of various time‐resolved spectroscopies, especially transient absorption (TA). For example, the properties and reaction mechanisms of the ketyl radical and the radical from the solvent and their reaction to produce a light absorbing transient (LAT) have been reported . The intersystem crossing from S 1 to T 1 for BP and its derivatives has been observed directly by ultrafast TA with measured rates of ~10 11 s –1 , and a rapid water addition process to the protonated BP triplet was identified to result in the fast deactivation of the triplet BP in acidic aqueous solution .…”

“…For example, the properties and reaction mechanisms of the ketyl radical and the radical from the solvent and their reaction to produce a light absorbing transient (LAT) have been reported. [26][27][28][29][30] The intersystem crossing from S 1 to T 1 for BP and its derivatives has been observed directly by ultrafast TA with measured rates of~10 11 s -1 , [31,32] and a rapid water addition process to the protonated BP triplet was identified to result in the fast deactivation of the triplet BP in acidic aqueous solution. [33] Moreover, nanosecond timeresolved resonance Raman (ns-TR 3 ) spectroscopy is an effective technique for further clearly characterizing the structural and electronic properties of transient species, and has been used to help identify the intermediates and photoproducts of BP and its derivatives.…”