Electron transfer sensitized photolysis of 'onium salts

Abstract

. Can. J. Chem. 66, 319 (1988). We have studied the anthracene-sensitized photolyses of both diphenyliodonium and triphenylsulphonium salts in solution using both steady-state and laser flash photolysis techniques. Photoproducts, namely, phenylated anthracenes along with iodobenzene or diphenylsulphide, respectively, are obtained from both salts with quantum efficiencies of ca. 0.1 at 375 nm. We infer the intermediacy of diphenyliodo and triphenylsulphur radicals formed by single electron transfer from the singlet-excited anthracene. We have developed a quantitative model of this chemistry, and identify the principal sources of inefficiency as back electron transfer, which occurs at nearly the theoretically limiting rate, intersystem crossing from the initially formed sensitizer-'onium salt encounter complex, and in-cage radical recombination. Faisant appel aux techniques de 1'Ctat stationnaire et de la photolyse laser eclair, on a CtudiC la ptiotolyse sensibiliske par l'anthrackne des sels de diphCnyliodonium et de triphCnylsulfonium en solution. Pour chacun des sels, a 375 nm, les efficacitCs quantiques en photoproduits, soit des anthracknes phtnylCs ainsi que respectivement de l'iodobenzkne et du sulfure de diphenyle, sont d'environ 0 , l . On en dCduit que les radicaux diphCnyliodo-et triphCnylsoufre se forment comme intermCdiaires par le transfert d'un Clectron de l'anthrackne excitC singulet. On a dCvelopp6 un modkle quantitatif de cette chimie et on a identifit que les principales causes de I'inefficacitC sont un transfert en retour d'tlectron qui se produit a une vitesse proche de la limite thkorique, un passage intersystkme se produisant a partir du complexe de rencontre sensibilisateur-sel onium qui se forme initialement et une recombinaison radicalaire se produisant dans la cage.[Traduit par la revue]

Photophysics of bis(p-N,N-dimethylamino)benzylidene acetone: Does photoinduced electron transfer occur from a twisted excited state?

“…We have already established, in similar photolyses with aromatic hydrocarbon sensitizers, that benzene (emission at 7.55 ppm) is a cage-escpae product ( p < 0) (10). The sign of the product, Ag-a, was inferred from a similar experiment with the structurally related Michler's Ketone as the sensitizer.…”

“…The electron transfer sensitization mechanism has considerable precedent in the sensitized photochemistry of 'onium salts (8)(9)(10)19).…”

“…If the quantum yield for photolysis via the-encounter complex reflects the competition between decomposition of the diphenyliodo radical (which occurs in ca. 250 ps (10)) and back electron transfer in the radical pair, the latter process would have to occur with a rate constant of ca. 4 X 1010 s : l , i.e., in 25 ps.…”

“…As with our previous study (10) of anthracene sensitized photolysis of the diphenyliodonium cation, several lines of investigation have proved fruitful in elucidating the pathways responsible for electron transfer sensitization with DMBA: photo-CIDNP experiments; quantum yield measurements for the photobleaching of the DMBA chromophore; picosecondresolved transient absorption spectroscopy; and kinetic analysis of the results obtained in these and the steady-state irradiations. It is thus a further intent of this paper to correlate these observations with the photophysical insights.…”

Direct and Sensitized Photolysis of Cyclic Iodine Compounds as Photo-acid Generator

“…On the other hand, BIO-Cl with AN hardly generated acid upon irradiation while that AN sensitizes iodonium salt PAGs as a singlet sensitizer for electron transfer Figure 3. Concentration of generated acid (normalized by the initial concentration of PAG) by direct irradiation (254 nm) from BIO-Cl (■), BIO-BF 4 (▲), BIO-OTs (◆), and BIO-Cl under argon (•) in acetonitrile was reported [6]. The oxidation potential of AN may not match BIO-Cl.…”