Use reflectance studies of β-phenylpropiophenone and benzophenone inclusion complexes with calix[4],[6] and [8]arenes

The formation of inclusion complexes of beta-phenylpropiophenone and benzophenone with p-tert-butylcalix [4], [6] and [8] arenes (powdered solid samples) was studied with the use of diffuse reflectance techniques. Experimental evidence was obtained for inclusion in all cases. The benzophenone n --> pi* absorption band exhibits hypsochromic shifts with an increase of the calixarene ring aperture, providing evidence for an increase in cavity polarity. beta-Phenylpropiophenone exhibits strong room temperature phosphorescence in contrast to its solution behaviour, and this is a clear evidence for the inclusion of this probe within the calixarene molecules. Calix [4] arene and calix [8] arene provide a more rigid environment to beta-phenylpropiophenone whereas calix [ 6] arene appears to be more flexible. Transient absorption spectra of inclusion complexes with benzophenone (1 : 1 mol : mol, excited at 355 nm) show major triplet formation in the calix [4] arene case, while the ketyl radical of benzophenone is formed in the calix [6] arene case and is predominant in the calix [ 8] arene case. Phenoxyl radical transient absorption also becomes evident in the last two cases. For beta-phenylpropiophenone (1 : 1 mol : mol) phenoxyl radicals are formed but no evidence was found for triplet or ketyl radical formation of this ketone in the calix [4] arene case. However, strong support for the ketyl radical of the aryl alkyl ketone was found for calix [6] arene and calix [8] arene inclusion complexes.