STUDIES ON RADICAL CATIONS .5. LASERFLASH-PHOTOLYSIS OF THE PARA-CHLORANIL-NAPHTHALENE SYSTEM - CHARACTERIZATION OF THE NAPHTHALENE RADICAL CATION IN A FLUID MEDIUM

Excitation of p‐Chloranil (CA) in propylcyanide (PrCN) at room temperature leads to rapid production of 3CA* which decays predominantly to CAH· with k d0 = 1.6 · 105 s−1. Observation of a photoinduced current suggests simultaneous production of CA− formed by electron transfer quenching of 3CA* by the medium. Added naphthalene (NP) quenches 3CA* with kq = 7.0 · 109M−1S−1; NP+ is unambigously identified as product (besides CA−) of the electron transfer process. Dissociation of the ion pair occurs with essentially unit probability. Higher concentrations of NP lead to the formation of (NP)+2. Pertinent spectroscopic parameters established for NP+ under the conditions used are λmax = 685 nm (ϵ = 2970) using the known parameters of CAdocumentclass{article}pagestyle{empty}begin{document}$ 1^{+ atop dot{}} $end{document} as reference. NP+ and CAdocumentclass{article}pagestyle{empty}begin{document}$ 1^{+ atop dot{}} $end{document} decay by charge annihilation with kr = 4.5 · 109 M−1S−1. The deviation from the diffusion controlled rate constant expected for ionic species, is discussed in view of the spin characteristics of the process. Comparison with two other ion recombination reactions leads to the conclusion that ‘inverted behaviour’ as expected from Marcus' theory does also not show up for backward e−‐transfer between two ions (produced by forward e−‐transfer between two neutrals). Residual absorptions in the system are ascribed to CAH·, tentatively proposed to originate from H+‐abstraction by CAdocumentclass{article}pagestyle{empty}begin{document}$ 1^{+ atop dot{}} $end{document} from the solvent. NP+ appears to be a rather stable species with respect to the medium if the latter is meticulously purified. Copyright © 1979 Verlag GmbH & Co. KGaA, Weinheim