Photolysis pyridinium ions

In a series of papers that appeared shortly after Gafney and Adamson s report, Meyer, Whitten, and co-workers explored bimolecular photoinduced ET reactions between Ru(bpy) + and a series of mild organic oxidants and reduc-tants [19-23]. Their first communication reported flash photolysis studies which demonstrated that Ru(bpy) + could efficiently reduce pyridinium ions such as 3 and 4 (Scheme 3), e.g. [19],... 

Type I aziridines can be prepared via photolysis of functionalized pyridinium ions. Mariano and co-workers have shown that irradiation of pyridinium ion 40 via a 450 W Hanovia lamp with Vycor filter will induce a ring contraction to produce a fused-bicyclic aziridine moiety 41 (Equation 16) <1996JOC4439>. The azabicyclo[3.1.0]hexane prepared through this method can rapidly experience nucleophilic opening to produce an amine-substituted cyclo-pentene. 

Figure 2.12. TRIR difference spectra observed over the first 0.5 ps following 266 nm photolysis (10 ns, 0.4 mJ) of pyridinium ion 30 and its N-labeled analog (8 inM) in argon-saturated acetonitrile-da-...

Moran, R. J. and Falvey, D. E., Photogenerated diarylnitrenium ions laser flash photolysis and product studies on diphenylnitrenium ion generated from photolysis of l-(N,N-dipheny-lamino)pyridinium ions,/. Am. Chem. Soc., 118, 8965, 1996. 

Free radical promoted, cationic polymerization also occurs upon irradiation of pyridinium salts in the presence of acylphosphine oxides. But phosphonyl radicals formed are not oxidized even by much stronger oxidants such as iodonium ions as was demonstrated by laser flash photolysis studies [51, 52]. The electron donor radical generating process involves either hydrogen abstraction or the addition of phosphorus centered or benzoyl radicals to vinyl ether monomers [53]. Typical reactions for the photoinitiated cationic polymerization of butyl vinyl ether by using acylphosphine oxide-pyridinium salt combination are shown in Scheme 10. 

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