Oxidation Potential of Intramolecular Exciplex on a Vinyl Copolymer as Estimated by Electron-transfer Quenching Reactions

Abstract

In the electron-transfer reaction from the fluorescent intramolecular exciplexes of a copolymer containing phenanthrene and N,N-dimethylaniline moieties, and of a model compound to electron acceptors, the reactivity of the exciplexes was studied kinetically in polar and nonpolar media. The copolymer was poly(9-vinylphenanthrene-co-p-dimethylaminostyrene) and the model compound was N,N-dimethyl-4-[3-(9-phenanthryl)propyl]aniline. The oxidation potential of the exciplex was evaluated by the relation of the exciplex-quenching rate constants to the reduction potentials of electron-accepting quenchers according to the equations of Rehm and Weller. It was found that the electron-donating ability of these intramolecular exciplexes resembled with each other and was larger than that of excited phenanthrene. In polar media the donating ability was very close to that of the phenanthrene anion radical.

Phosphoryl- and thiophosphoryl-dithioformates. Part IV. Electrochemical reduction and EPR study of the radical anions †‡

“…These trends are consistent with those previously reported for a number of dithio-and monothio-benzoates as well as for some alkoxycarbonyl-substituted dithio-and monothio-formates. [20][21][22][23] The values collected in Table 1 also indicate that changing from the phosphoryl to the thiophosphoryl group did not significantly affect either the reduction potentials of the dithioformates or the lifetime of their radical anions; similar substitution in both types of monothioesters, while not leading to large variations in the reduction potentials, resulted in a remarkable enhancement of the stability of the reduced species. The present results indicate that the phosphoryl and thiophosphoryl groups exert a substantially similar electron-withdrawing effect, which, from the data in Table 2, is estimated to be between those of the phenyl and of the methoxycarbonyl groups.…”

Light-Induced Alkylation of (Hetero)aromatic Nitriles in a Transition-Metal-Free C–C-Bond Metathesis

“…Alternatively, phenanthrene can be used as a photoredox catalyst, which proved to be suitable for radical alkylations of aromatic nitriles . Fluorescence quenching experiments indicate that the excited singlet state of phenanthrene [ E 1/2 (Phen •+ / 1 [Phen]*) = −2.1 V vs SCE] readily reduces aromatic nitriles such as 4-cyanopyridine [ 1a , E 1/2 ( 1a / 2a ) = −1.66 V vs SCE] to the corresponding radical anions 2a (oxidative quenching). The resulting phenanthrene radical cation is a strong electron acceptor [ E 1/2 (Phen •+ /Phen) = +1.50 V vs SCE] capable of oxidizing tertiary amines such as (±)-laudanosine ( 3a ) .…”

Transition-Metal-Free Decarboxylative Photoredox Coupling of Carboxylic Acids and Alcohols with Aromatic Nitriles

“…Irradiation with UV light produces an excited state of phenanthrene ( 24 ) (for absorption spectra see Figure S1 in the Supporting Information). Fluorescence quenching experiments strongly indicate that an oxidative quenching cycle is operating, starting with an electron transfer from excited phenanthrene to the nitrile ( E 1/2 (Phen •+ / 1 [Phen]*) = −2.1 V vs SCE; for 1,4-dicyanobenzene E 1/2 (DCB/DCB •– ) = −1.61 V vs SCE). , The resulting radical cation of phenanthrene is a strong oxidant ( E 1/2 (Phen •+ /Phen) = +1.50 V vs SCE), and it is well established that this species causes decarboxylation of carboxylates 26 (for Boc-Pro-OCs E 1/2 red = +0.95 V vs SCE) by single-electron oxidation. ,− ,, Decarboxylation of cesium oxalates of type 27 (for t BuOCOCO 2 Cs E 1/2 red = +1.28 V vs SCE) should also be feasible. Combination of the nitrile’s radical anion 25a with the alkyl radical 28 formed by decarboxylation affords anion 29 , which is stabilized by the elimination of cyanide .…”