Ionic photodissociation of excited electron donor-acceptor systems. II. Importance of the chemical property of donor-acceptor pairs

Abstract

The relationship between the ionic photodissociation yield and the electron donor-acceptor interaction of pyrene-quencher systems was investigated by nanosecond laser photolysis and transient photocurrent measurements. While no general relation was obtained, the chemical property of donor-acceptor pairs was found to be reflected in the yield. On the basis of the present and previous results it was concluded that the ionic photodissociation process consists of two steps, namely, the encounter collisional electron transfer and the orientational relaxation of solvents. With the latter process some other radiationless transitions depending on the chemical property compete in the dissociative excited state. It was shown in the case of pyrene-nitrile systems that an unknown quenching process, other than ionic dissociation as well as triplet formation, increases with the electron affinity.

Photoinduced Electron Transfer Reactions of Hexarhenium(III) Cluster: Oxidative Quenching of [Re6S8Cl6]4− Emission by Electron Acceptors

“…2. In the [Re 6 ] 4--PDA system, we observed transient absorption in the wavelength (k) region of 500-700 nm, which was assigned safely to the anion radical of PDA as reported by Hino et al [32]. Unfortunately, however, we could not detect the absorption band of [Re 6 ] 3-in the k region studied.…”

“…4 /M/cm [32], we evaluated the decay time constant of the PDA anion radical to be 2.7 9 10 8 /M/s. As a reference system producing an electrostatically-attractive product ion pair by PET, we also studied transient absorption of a pyrene (Py)-PDA system as shown in Fig.…”

The Energetics of Electron‐transfer Reactions of Chlorophyll and Other Compounds*

“…(1972) noted rapid drop-off in ion yield with solvent polarity in the pyrene-dimethylaniline system when W' = E; -EA exceeded Wr'] = W* -U [ * ] . In reactions of pyrene with a number of acceptors in acetonitrile, Hino et al (1976) found that the yield of ions increased as the energy of the ion pair calculated by Eq. 23 increased.…”

Role of Polar Protic Solvents in the Dissociation and Reactivity of Photogenerated Radical Ion Pairs

“…Of particular relevance are small-molecule radical ions, which have shown interesting reactivity in protic media. − Importantly, these photogenerated radicals are neither the result of electronic transitions that occupy a high-lying orbital by depopulating a low-energy orbital in the same molecule nor the outcome of molecular cleavage (Scheme ). The study of photogenerated charged organic radicals impulsively generated in solution via photolysis of π-stacked CT complexes dates back to their use as a testing ground for Marcus electron transfer theory and as model systems for exciplexes. − Photogenerated ion pairs have been shown to possess strongly environment-dependent properties affecting the yield and recombination rates of free ions, − as well as the ability of charges to either be localized or delocalized over several molecules . Therefore, photolysable CT complexes of substituted aromatic molecules in solution represent an ideal system to study the evolution of radical ions in their ground electronic state.…”