OPTICAL SPECTROSCOPY OF THE ARYL CATION .2. MATRIX EFFECTS ON THE PRODUCTION OF 3AR+

Low-temperature UV and visible light photolyses of the diazonium salt 2,5-di-n-butoxy-4-morpholinobenzenediazonium tetrafluoroborate yield intermediates whose nature depends on the matrix, as determined by optical and electron spin resonance spectroscopy. The corresponding aryl radical and aryl cation are produced in various ratios in different matrices. Thus the aryl radical appears as the sole species in hydrocarbon matrices, and the aryl cation is observed as the only species in a sulphuric acid matrix. The lambda-max value of the absorption band of the aryl cation is located at 465 nm and is independent of the matrix. The aryl radical absorption occurs over the range 308-320 nm depending on the matrix, which reflects a distinct change in the dipole moment on going from a more polar state to a less polar state.