Cage escape and spin rephasing of triplet ion-radical pairs: temperature-viscosity and magnetic field effects in photoreduction of fluorenone by dabco

Periasamy, N.; Linschitz, Henry

doi:10.1016/0009-2614(79)80513-8

Cited by 28 publications

(16 citation statements)

References 14 publications

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“…Equations of the type (21) have been applied successfully e. g. for the determination of dipole moments of exciplexes in solvents of dielectric constants smaller than about 10 [5,49]. For solvents with higher dielectric constants these equations fail since (e -1)/(2e + 1) approaches a limiting value of 0.5, whereas even in the region of e between 30 and 80 drastic solvent shifts of charge transfer transitions can be observed.…”

Section: Radical Yieldsmentioning

confidence: 99%

See 1 more Smart Citation

Heavy Atom Substituents as Molecular Probes for Solvent Effects on the Dynamics of Short‐lived Triplet Exciplexes

Winter

Steiner

1980

Ber Bunsenges Phys Chem

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The influence of heavy atom substituents (Br, I) in the electron donor aniline on the electron transfer reaction with thiopyronine triplet is investigated by flash spectroscopy in solvents of different viscosity and polarity. Triplet quenching constants and radical yields are determined. The results are analysed in terms of decay constants of an intermediate triplet exciplex where the heavy atom substituents significantly enhance the intersystem crossing process leading to singlet ground state formation and thus diminishing the radical yield due to exciplex dissociation. The sensitivity of the radical yield to solvent effects is strongly enhanced by heavy atom substitution though the solvent effects proper on the exciplex dynamics are substituent independent. The heavy atom effect is used to study the solvent cage effect on exciplex dissociation by means of viscosity variation. The exciplex dissociation lifetime is proportional to solvent viscosity, however, it contains a constant contribution which may be attributed to exciplex bonding. By means of the heavy atom probes it is found that increasing solvent polarity intersystem crossing in the exciplex is favored over exciplex dissociation into radicals. A tentative explanation is given in terms of solvent polarity dependence of the electronic energy gap between exciplex and corresponding Franck-Condon ground state. (1) and (2) it follows that the radical yield is determined by three factors, characterizing the behaviour of the triplet exciplex (Eq. (4» where 'Hal is the atomic spin-orbit coupling constant of the halogen and C 2 (POSHaJ is the Hiickel spin density transferred to the position of the halogen atom by the electron transfer. The latter factor readily explains the positional dependence of the substituent effect (para > ortho > meta).(1)The rate determining step in the quenching of the excited cationic dye triplet eA +) by the electron donor (D) is the formation of a triplet exciplex with radical-pair-like electronic structure e(A'D +». The triplet exciplex has two decay channels: dissociation to the free radicals (rate constant k fr ) and intersystem crossing with back transfer of the electron to the donor leading to the formation of the ground state of the reaction partners (rate constant k isc ) ' The radical yield observed is determined by the two decay constants of the exciplex:triplet exciplexes can be detected by their phosphorescence under such conditions. In a recent paper [22] we provided indirect evidence for the formation of triplet exciplexes as intermediates in electron transfer reactions. We studied the reaction of thionine triplet as an electron acceptor with aniline and its monohalogen derivatives as electron donors in methanol. In these reactions the halogen substituents have systematic influence on the radical yield (extrapolated to complete triplet quenching) which could be explained satisfactorily by the following mechanism, strongly supported by a recently determined magnetic field effect [23]:The analysis of the radical yield...

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Section: Radical Yieldsmentioning

confidence: 99%

“…So far, however, geminate recombinations have been detected mainly with radical pairs subject to Coulomb attraction (see e. g. Ref. [14,48,49]). Without Coulomb interaction as in our systems the effects are expected to be much smaller [50].…”

Section: Influence Of Solvent Viscositymentioning

confidence: 99%

Heavy Atom Substituents as Molecular Probes for Solvent Effects on the Dynamics of Short‐lived Triplet Exciplexes

Winter

Steiner

1980

Ber Bunsenges Phys Chem

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“…However, in the presence of a weak MF of the order of hyperfine interaction (HFI) or higher the degeneracy of the triplet states is removed and only S → T 0 channel is operative, thus leading to an increase in the population of the initial spin state. Generally MF studies are performed in micellar media or highly viscous solvents where the RIPs retain their geminate character for longer time to allow the occurrence of diffusion and subsequent spin flipping [14,15].…”

Section: Introductionmentioning

confidence: 99%

Exploring photoinduced electron transfer and excited-state proton transfer reactions involving 9-aminoacridine hydrochloride hydrate and methyl viologen using laser flash photolysis

Mitra

Chakraborty

Basu

2014

Chemical Physics Letters

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“…Therefore, an optimum distance of separation between the RIPs is required so that both spin flipping and recombination are feasible. Generally MFE experiments on the triplet born transients involve micellar media [16,17] or highly viscous solvents [18][19][20] at low temperature or long chain biradicals [21,22] to reduce fast escape thus retaining the spin-correlation between the partners of the geminate RIP. However, there are few examples found in the literature, where MFE has been detected in homogeneous medium by transient absorption of the triplets and the radical ions [23][24][25][26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Direct observation of radical intermediates during electron transfer between DNA and a ternary copper complex

Dey

Basu

2011

Journal of Luminescence

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Cage escape and spin rephasing of triplet ion-radical pairs: temperature-viscosity and magnetic field effects in photoreduction of fluorenone by dabco

Cited by 28 publications

References 14 publications

Heavy Atom Substituents as Molecular Probes for Solvent Effects on the Dynamics of Short‐lived Triplet Exciplexes

Heavy Atom Substituents as Molecular Probes for Solvent Effects on the Dynamics of Short‐lived Triplet Exciplexes

Exploring photoinduced electron transfer and excited-state proton transfer reactions involving 9-aminoacridine hydrochloride hydrate and methyl viologen using laser flash photolysis

Direct observation of radical intermediates during electron transfer between DNA and a ternary copper complex

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