Chain-amplified photochemical fragmentation of N-alkoxypyridinium salts: proposed reaction of alkoxyl radicals with pyridine bases to give pyridinyl radicals.

Photoinduced electron transfer to N-alkoxypyridiniums, which leads to N–O bond cleavage and alkoxyl radical formation, is highly chain amplified in the presence of a pyridine base such as lutidine. Density functional theory calculations support a mechanism in which the alkoxyl radicals react with lutidine via proton-coupled electron transfer (PCET) to produce lutidinyl radicals (BH•). A strong electron donor, BH• is proposed to reduce another alkoxypyridinium cation, leading to chain amplification, with quantum yields approaching 200.

N,N'-Bis(2,2,3,3,4,4,4-hepta-fluoro-butyl)naphthalene-1,4:5,8-tetra-carboximide.

The title mol-ecule, C(22)H(8)F(14)N(2)O(4), lies across a crystallographic inversion center with the naphthalene diimide core essentially planar (mean deviation from plane is 0.0583 Å). The CF(2) groups in the perfluorobutyl chains are in an energetically favorable all trans conformation.

Enhancement of chain amplification in photoreactions of N-methoxypyridinium salts with alcohols.

Recently we reported a chain-amplified photochemical reaction, initiated by electron transfer from an excited sensitizer to N-methoxypyridinium salts, which leads to N-O bond cleavage (26). Hydrogen atom abstraction by the methoxy radical from an alcohol yields an alpha-hydroxy radical, which reduces another N-methoxypyridinium molecule and propagates the chain. We now report that the chain amplification can be significantly enhanced in the presence of water.

Chain amplification in photoreactions of N-alkoxypyridinium salts with alcohols: mechanism and kinetics.

Photosensitized electron transfer from a variety of singlet- and triplet-excited donors to N-methoxypyridinium salts leads to N-O bond cleavage. Hydrogen atom abstraction by the resulting methoxy radical from an added alcohol generates an alpha-hydroxy radical that reduces another pyridinium molecule, thus leading to chain propagation. For example, thioxanthone-sensitized reactions of 4-cyano-N-methoxypyridinium, P1, with several aliphatic and benzyl alcohols gave quantum yields for products formation (an aldehyde or a ketone and protonated 4-cyanopyridinium) of approximately 15-20, at reactant concentrations of approximately 0.