Electrochromism and charge transfer in molecular complexes and autocomplexes

Blinov, L. M.; Кириченко, Н. А.; Bespalov, B. P.; Rumyantsev, V. G.

doi:10.1007/bf00743289

Cited by 2 publications

(2 citation statements)

References 4 publications

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“…68,69 An alternate candidate for a dark intermediate state would be a charge-transfer state that has been postulated to play a role in SF. 3,21 The charge-transfer states of tetracene that have been identified through electroabsorption spectroscopy are higher in energy than the Frenkel exciton, 70,71 but it is possible that rapid lattice distortion after singlet excitation leads to a dark state with charge-transfer character. 10 However, there is no sign of this state at 77 K as either a long-lived induced absorption in the transient absorption or in the form of excimer emission.…”

Section: Resultsmentioning

confidence: 99%

The dependence of singlet exciton relaxation on excitation density and temperature in polycrystalline tetracene thin films: Kinetic evidence for a dark intermediate state and implications for singlet fission

Burdett

Gosztola

Bardeen

2011

The Journal of Chemical Physics

172

234

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The excited state dynamics of polycrystalline tetracene films are studied using femtosecond transient absorption in combination with picosecond fluorescence, continuing work reported in an earlier paper [J. J. Burdett, A. M. Muller, D. Gosztola, and C. J. Bardeen, J. Chem. Phys. 133, 144506 (2010)]. A study of the intensity dependence of the singlet state decay is conducted to understand the origins of the discrepancy between the broadband transient absorption and fluorescence experiments seen previously. High-sensitivity single channel transient absorption experiments allow us to compare the transient absorption dynamics to the fluorescence dynamics measured at identical laser fluences. At high excitation densities, an exciton-exciton annihilation rate constant of ~1 × 10(-8) cm(3) s(-1) leads to rapid singlet decays, but at excitation densities of 2 × 10(17) cm(-3) or less the kinetics of the transient absorption match those of the fluorescence. At these lower excitation densities, both measurements confirm that the initially excited singlet state relaxes with a decay time of 80 ± 3 ps, not 9.2 ps as claimed in the earlier paper. In order to investigate the origin of the singlet decay, the wavelength-resolved fluorescence dynamics were measured at 298 K, 77 K, and 4 K. A high-energy J-type emitting species undergo a rapid (~100 ps) decay at all temperatures, while at 77 K and 4 K additional species with H-type and J-type emission lineshapes have much longer lifetimes. A global analysis of the wavelength-dependent decays shows that the initial ~100 ps decay occurs to a dark state and not via energy transfer to lower energy bright states. Varying the excitation wavelength from 400 nm to 510 nm had no effect on the fast decay, suggesting that there is no energy threshold for the initial singlet relaxation. The presence of different emitting species at different temperatures means that earlier interpretations of the fluorescence behavior in terms of one singlet state that is short-lived due to singlet fission at high temperatures but long-lived at lower temperatures are probably too simplistic. The presence of a rapid singlet decay at all temperatures indicates that the initially created J-type singlet exciton decays to an intermediate that only produces free triplets (and delayed fluorescence) at high temperatures.

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Section: Resultsmentioning

confidence: 99%

The dependence of singlet exciton relaxation on excitation density and temperature in polycrystalline tetracene thin films: Kinetic evidence for a dark intermediate state and implications for singlet fission

Burdett

Gosztola

Bardeen

2011

The Journal of Chemical Physics

172

234

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“…a) Quantum efficiency of pulse photoconductivity Y for Pc layers as a function of 1/T at hv = = 2.4 eV; b) corresponding T dependence of thermalization length yo 0-30 excited molecule first dissipates its energy via intramolecular conversion and may ionize only from a long-lived S, state, forming a C P state with a constant separation length ro of the order of the intermolecular spacing. I n this case, too, there may be another independent pathway of C P state population via optical CT transition, which has been detected in CuPhc and H,Phc layers by Blinov and Kirichenko [30], using electroabsorption technique. Since both C P state population channels yield apparently only deep-lying C P states, the quantum efficiency @ of Phc is small, being of the order of lo-* to electrons/photon [29].…”

Section: Cp State Populationmentioning

confidence: 87%

On Charge Carrier Photogeneration Mechanisms in Organic Molecular Crystals

Silinsh

Kolesnikov

Muzikante

et al. 1982

Physica Status Solidi (b)

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An extended phenomenological model of photogeneration mechanisms in organic molecular crystals is proposed which describes intermediate and final stages of multi‐step photogeneration processes in terms of a modified Onsager approach. It is shown that the intermediate geminate charge pair (CP) states can be populated through two independent competitive pathways: viz. via autoionization and subsequent hot electron thermalization in terms of a ballistic model and via optical charge transfer (CT) transitions. The thermalization processes and their dependence on photon energy, temperature, and electric field are studied in some detail. It is demonstrated that the threshold spectral dependence of intrinsic photoconductivity quantum efficiency β(hv) in anthracene‐type crystals is mainly determined by the spectral dependence of dissociation efficiency Ω(hv) of the intermediate CP‐states and can be approximated by Onsager's formula.

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Electrochromism and charge transfer in molecular complexes and autocomplexes

Cited by 2 publications

References 4 publications

The dependence of singlet exciton relaxation on excitation density and temperature in polycrystalline tetracene thin films: Kinetic evidence for a dark intermediate state and implications for singlet fission

The dependence of singlet exciton relaxation on excitation density and temperature in polycrystalline tetracene thin films: Kinetic evidence for a dark intermediate state and implications for singlet fission

On Charge Carrier Photogeneration Mechanisms in Organic Molecular Crystals

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