Mechanism of Exciplex Decay: The Quantum Yields and the Rate Constants of Triplet Formation from 9-Cyanophenanthrene Exciplexes

Dogadkin, D. N.; Dolotova, E. V.; Соболева, И. В.; Kuz’min, M. G.; Plyusnin, B. F.; Pozdnyakov, Ivan P.; Grivin, Vjacheslav P.; Phillips, David; Murphy, Keefe

doi:10.1023/b:hiec.0000048236.18451.db

Cited by 5 publications

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“…Englman and Jortner [25] derived another expression, developing their version of the theory of radiationless processes in the low-temperature (hν V Ӷ k B T) approximation of weak interaction (λ V ~≤ hν V ): ) and the energy of 0-0 transitions ( ); the spectral factor (S = λ V /hν V ); the energy of the dominant high-frequency modes (hν V ); the energy of internal reorganization of reactants (λ V ); Gaussian broadening in the emission spectra of 9-cyanophenanthrene (CP) exciplexes with 1,2,3-and 1,3,5-trimethoxybenzenes (123TMB and 135TMB) (σ, exciplex lifetimes ( ); the singlet-triplet splitting ∆E ST in exciplexes; the quantum yields of exciplex emission ( ), triplets ( ), radical ions ( ), and internal conversion ( ) from exciplexes; and the rate constants of intersystem crossing ( ) and internal conversion ( ) in exciplexes [22,23] …”

Section: Photochemistrymentioning

confidence: 99%

“…In the previous works [22,23], we measured the quantum yields of fluorescence ( ) of exciplexes of 9-cyanophenanthrene (CP) with 1,2,3-and 1,3,5-trimethoxybenzenes (123TMB and 135TMB), the quantum yields of formation from these of triplet states ( ) and of radical ions ( ), and the rate constants of internal conversion and intersystem crossing of these exciplexes in solvents of different polarities. The experimental methods and the procedures of the determination of the quantum yields of formation of triplets, radical ions, and internal conversion were described elsewhere [22,23].…”

mentioning

confidence: 99%

“…The experimental methods and the procedures of the determination of the quantum yields of formation of triplets, radical ions, and internal conversion were described elsewhere [22,23]. The data are listed in Table 1.…”

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The nature of internal conversion and intersystem crossing in exciplexes

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1 More and more data to suggest that many types of electron transfer processes, in particular photoinduced electron transfer between organic molecules in the kinetic region (at a free energy of excited-state electron transfer of ∆ > -0.4 eV), occur via the mechanism of intermediate formation of exciplexes [1][2][3][4][5][6], rather than the generally accepted mechanism of the preceding thermally activated solvent reorganization [7][8][9][10], are appearing in the literature. According to the mechanism of intermediate formation of exciplexes, the apparent rate constant of quenching of excited molecules is equal to k Q = 1/[1/ k 1 + exp ( ∆ / RT )] , where k 1 is the rate constant of exciplex formation, which is close to the diffusion rate constant; = 1/( + + + ) is the exciplex lifetime; ∆ is the Gibbs energy of exciplex formation; and , ,, and are the rate constants of exciplex emission, internal conversion and intersystem crossing of exciplexes, and exciplex dissociation into radical ions, respectively. Competition between different processes of exciplex decay determines not only the quantum yields of primary products of electron transfer but also the magnitude of the rate constants of quenching of excited molecules. Internal conversion and intersystem crossing, which involve partial back charge transfer and lead to either the initial singlet ground state or the triplet state of reactants, are the major processes of the exciplex decay. The back electron transfer in the radical ion pairs has been extensively investigated by many researchers [11][12][13][14][15][16][17][18][19][20][21], especially in view of the fact that it is for these exciplexes that a decrease in the rate of electron transfer with an increase in the reaction exoergicity (free energy of back electron transfer ∆ G BET = electron transfer) predicted by the Marcus theory (inverted region) [11][12][13][14][15][16][17][18][19][20][21] was observed.In order to reveal most important factors governing the rate of internal conversion and intersystem crossing in exciplexes, we will consider two alternative mechanisms, the thermally activated electron transfer and radiationless quantum transition. An analysis of experimental data shows that it is more sound to consider both internal conversion and intersystem crossing (back electron transfer) in exciplexes as radiationless electronic-vibrational diabatic quantum transitions rather than thermally activated electron transfer.In the previous works [22,23], we measured the quantum yields of fluorescence ( ) of exciplexes of 9-cyanophenanthrene (CP) with 1,2,3-and 1,3,5-trimethoxybenzenes (123TMB and 135TMB), the quantum yields of formation from these of triplet states ( ) and of radical ions ( ), and the rate constants of internal conversion and intersystem crossing of these exciplexes in solvents of different polarities. The experimental methods and the procedures of the determination of the quantum yields of formation of triplets, radical ions, and internal conversion were described elsewhere [22,23]. The d...

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Section: Photochemistrymentioning

confidence: 99%

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The nature of internal conversion and intersystem crossing in exciplexes

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“…Temperature Effect on the Competition between the Processes of 9-Cyanophenanthrene Exciplex Decay respectively), for which the rate constants and the decay quantum yields at ambient temperature had been determined earlier [22,23]. We studied experimentally the temperature effect in the range of 230-300 K on the competition between exciplex decay reactions.…”

Section: Photochemistrymentioning

confidence: 99%

“…It is well documented that the main pathways of exciplex decay are fluorescence, internal conversion, and intersystem crossing in both nonpolar and polar solvents [17][18][19] and dissociation into radical ions in polar solvents [20][21][22][23]. Determining the thermodynamic and activation parameters for exciplex formation and decay, we assumed [13][14][15] that the exciplex decay could be characterized by the same mean activation entropy and enthalpy over the entire temperature range examined, although their contribution could vary with temperature because of competition between several processes.…”

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Temperature effect on the competition between the processes of 9-cyanophenanthrene exciplex decay

et al. 2005

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The activation parameters of internal conversion, intersystem crossing, and dissociation into radical ions were determined for the exciplexes of 9-cyanophenanthrene with 1,3,5-and 1,2,3-trimethoxybenzene. The activation enthalpies for the different processes of exciplex decay were found to be close for a given exciplex in a given solvent, thus allowing a linear approximation for the temperature dependence of the logarithm of the exciplex lifetime.

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The Behavior of Exciplex Decay Processes and Interplay of Radiationless Transition and Preliminary Reorganization Mechanisms of Electron Transfer in Loose and Tight Pairs of Reactants

2006

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Exciplex emission spectra and rate constants of their decay via internal conversion and intersystem crossing are studied and discussed in terms of conventional radiationless transition approach. Exciplexes of 9-cyanophenanthrene with 1,2,3-trimethoxybenzene and 1,3,5-trimethoxybenzene were studied in heptane, toluene, butyl acetate, dichloromethane, butyronitrile, and acetonitrile. A better description of spectra and rate constants is obtained using 0-0 transition energy and Gauss broadening of vibrational bands rather than the free energy of electron transfer and reorganization energy. The coincidence of parameters describing exciplex emission spectra and dependence of exciplex decay rate constants on energy gap gives the evidence of radiationless quantum transition mechanism rather than thermally activated medium reorganization mechanism of charge recombination in exciplexes and excited charge transfer complexes (contact radical ion pairs) as well as in solvent separated radical ion pairs. Radiationless quantum transition mechanism is shown to provide an appropriate description also for the main features of exergonic excited-state charge separation reactions if fast mutual transformations of loose and tight pairs of reactants are considered. In particular, very fast electron transfer (ET) in tight pairs of reactants with strong electronic coupling of locally excited and charge transfer states can prevent the observation of an inverted region in bimolecular excited-state charge separation even for highly exergonic reactions.

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Mechanism of Exciplex Decay: The Quantum Yields and the Rate Constants of Triplet Formation from 9-Cyanophenanthrene Exciplexes

Cited by 5 publications

References 17 publications

The nature of internal conversion and intersystem crossing in exciplexes

The nature of internal conversion and intersystem crossing in exciplexes

Temperature effect on the competition between the processes of 9-cyanophenanthrene exciplex decay

The Behavior of Exciplex Decay Processes and Interplay of Radiationless Transition and Preliminary Reorganization Mechanisms of Electron Transfer in Loose and Tight Pairs of Reactants

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