Hydrogen abstraction in the neutral molecular cluster of benzophenone and hydrogen donors formed in a supersonic free jet expansion

Abstract

Photochemical reactions of benzophenone with hydrogen donors in neutral molecular clusters formed in a supersonic free jet expansion were studied. It was found that benzophenone undergoes photoreduction to form benzophenone ketyl radical in the benzophenone-1,4-cyclohexadiene mixed expansion. Good agreement between the action spectrum of the hydrogen abstraction reaction and the multiphoton ionization (MPI) spectrum of benzophenone-1,4-cyclohexadiene mixed clusters suggested that benzophenone ketyl radical is formed by an intracluster reaction after photoexcitation of benzophenone. This is the first observation of hydrogen abstraction in a neutral molecular cluster. However, no ketyl radical fluorescence is observed when ethanol, 2-propanol, or triethylamine is used as a hydrogen donor. The dependence of the cluster reactivity on the nature of the hydrogen donors is discussed.

[4-(Allyloxy)phenyl](phenyl)methanone

“…For more details of the synthesis, see: Prucker et al (1999). For photoreactive properties of benzophenone derivates, see: Shirahata & Kishimoto (1984); Dorman & Prestwich (1994); Beckett & Porter (1963); Kubo et al (2010); Balakirev et al (2005); Ferreira et al (1995); Matsushita et al (1992). For related structures, see: Schlemper (1982); Norment & Karle (1962); Guo et al (1992).…”

“…This substrate is a compound that has a benzophenone moiety which exhibits a known photoreactivity and is particularly useful in photopolymerizable organopolysiloxane and silicone resins Prucker et al, (1999);Shirahata & Kishimoto, (1984); Dorman & Prestwich, (1994); Beckett & Porter, (1963). When triggered by UV light (λ = 365 nm), a biradical triplet state is formed, which is able of abstracting a proton from any neighboring aliphatic C-H group to form a C-C bond (Ferreira et al, (1995); Balakirev et al, (2005); Kubo et al (2010)) and as a result of the photochemical reaction, a thin layer of the polymer is covalently bound to the surface (Prucker et al (1999); Shirahata & Kishimoto, (1984); Dorman & Prestwich, (1994); Matsushita et al (1992)). This molecule can be also copolymerized with other polymer molecules and will not migrate out through its double bond.…”

Dispersed fluorescence spectra of jet-cooled benzophenone ketyl radical: Assignment of the low-frequency vibrational modes

“…24 In their subsequent work, they reported the fluorescence excitation and dispersed emission spectra of BPK generated by the intracluster reaction between BP and 1,4-cyclohexadiene in the supersonic free jet. 25 These observed spectra were not sharp enough to resolve the vibronic structure of BPK because of the congestion of low-frequency van der Waals modes of BPK-1,4-cyclohexadiene clusters. Kawai et al 26 have also investigated photoreaction of BP in various BP/solvent molecule clusters and observed emissions of BPK and exciplexes.…”

Grafting of a Stimuli Responsive Polymer on Nanolayered Coextruded PS/PCL Films by Surface Initiated Polymerization

“…The radical abstracts a proton from a polymer in its vicinity, forming a benzophenone ketyl radical and a polymer radical. These radicals, then, recombine to form C‐C bonds . Thus, it can be attached to any surface with a C‐H group .…”

“…These radicals, then, recombine to form C-C bonds. [11][12][13] Thus, it can be attached to any surface with a C-H group. [ 14,15 ] It is particularly useful in attaching to chemically inert polymer surfaces (eg.…”