Radiation-generated cations of 1,1-diphenylethylene and their kinetic behaviour at low temperatures

Characterization of Persistent Intermediates Generated upon Inclusion of 1,1-Diarylethylenes within CaY Zeolite: Spectroscopy and Product Studies

“…Literature reports indicate that detection of radical cations from 6 and 9 is complicated by their rapid addition to the precursor alkene. , Nevertheless, we attempted to generate 6 .+ using the same sensitizers used for the other diarylethylenes. A transient species with λ max at 340 nm and a shoulder at approximately 400 nm was readily detected using N -methylquinolinium/toluene as sensitizer.…”

“…Although a number of groups have reported absorption characteristics of diarylethylene radical cations in glasses at low temperature and in solution, there are a number of inconsistencies in the reported data. ,, For example, attempted generation of diphenylethylene radical cation by either γ-irradiation in an organic glass or by pulse radiolysis at low-temperature results in one or more species with λ max at 390, 500−550 and 1200 nm. 19a-c It has been suggested that the 390 and 520 nm peaks are due to the dimer radical cation 19a while the 550 and 1200 nm bands are assigned to the monomer radical cation 19b. Later studies suggested that both monomer and dimer absorb in the 390 and 500 nm regions. 19d,e The rapid addition of the radical cation to its precursor makes it even more difficult to provide an unambiguous spectrum for the diphenylethylene radical cation in solution at room temperature. Similarly the radical cation of 1,1-di (4-methoxyphenyl) ethylene has been reported to absorb at 330, 390 and 580 nm in a 1-chlorobutane glass 19e.…”

“…Later studies suggested that both monomer and dimer absorb in the 390 and 500 nm regions. 19d,e The rapid addition of the radical cation to its precursor makes it even more difficult to provide an unambiguous spectrum for the diphenylethylene radical cation in solution at room temperature. Similarly the radical cation of 1,1-di (4-methoxyphenyl) ethylene has been reported to absorb at 330, 390 and 580 nm in a 1-chlorobutane glass 19e. Attempted generation of this radical cation and its 2-methyl substituted analogue by pulse radiolysis is reported to give a 400 nm maximum in dichloromethane, 20a,b whereas the 2,2-dimethyl analogue generated by photosensitized electron transfer has a reported λ max value of 760−800 nm 20c…”

Generation and Reactions of Organic Radical Cations in Zeolites

“…261 With the benefit of hindsight, these choices were unfortunate: 103 gave rise to the blue species (again assigned to 103 •+ ); 70 probed only the external surface because it is too large to pass through the 0.74 nm pore opening. 193 Pulse radiolysis studies produced "authentic" UV-Vis spectra of 103 •+ (λ max 550 nm) and a dimer radical cation, [103‚‚‚103] •+ , (λ max 520 nm), 337,338 both different from the maximum of the "blue species". However, nanosecond laser flash studies of p-substituted derivatives revealed that 103 •+ is highly reactive in solution and unlikely to be detected in pulse radiolysis.…”

“…Pulse radiolysis studies produced “authentic” UV−Vis spectra of 103 •+ (λ max 550 nm) and a dimer radical cation, [ 103 ··· 103 ] •+ , (λ max 520 nm), , both different from the maximum of the “blue species”. However, nanosecond laser flash studies of p -substituted derivatives revealed that 103 •+ is highly reactive in solution and unlikely to be detected in pulse radiolysis.…”