Influence of exciton transfer on the optical cycle of α-PTCDA

Scholz, Reinhard; Schreiber, Michael; Vragović, I.; Kobitski, Andrei Yu; Wägner, Hans; Zahn, Dietrich R. T.

doi:10.1016/j.jlumin.2004.01.028

Cited by 11 publications

(17 citation statements)

References 16 publications

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“…In the following, it will be demonstrated that several candidates for relaxed excited dimer states can be constructed from different deformation patterns of the two molecules involved. 48 As in Secs. V and VI, the dimer geometries investigated include pairs of the same basis molecule displaced along the a or b lattice vectors of ␣-PTCDA, a dimer of the two coplanar basis molecules in the unit cell, and two further noncoplanar dimers involving both kinds of basis molecules.…”

Section: Influence Of Internal Deformations On Ct Transitionsmentioning

confidence: 90%

“…The TD-DFT method results in CT transitions below the neutral excitations of the molecules constituting the dimer. 48 Due to the deficiency that the TD-DFT approach does not reproduce the correct asymptotics for CT states 49 and the lack of the crystalline surroundings this result seems somewhat arbitrary, but after the detailed discussion in the subsequent parts of this work, it turns out that the relative positions of the Frenkel and CT transitions along the stacking direction are reproduced with a systematic deviation of only about 0.18 eV, compare Sec. VIII D. In any case, the slowly decaying PL channels occuring energetically below the Frenkel exciton PL ͑Ref.…”

Section: Computational Schemesmentioning

confidence: 98%

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Investigation of molecular dimers inα-PTCDA byab initiomethods: Binding energies, gas-to-crystal shift, and self-trapped excitons

et al. 2005

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Time-dependent density functional theory ͑TD-DFT͒, Hartree-Fock, second-order Møller-Plesset perturbation theory ͑MP2͒, and configuration interaction of singly excited states ͑CIS͒ are applied to crystalline PTCDA ͑3,4,9,10-perylene tetracarboxylic dianhydride͒. The systems investigated include single molecules in an optimized rectangular shape, and molecules and molecular dimers compatible with the experimental geometry in the crystalline ␣-phase. Total energy calculations for pairs of adjacent molecules result in a microscopic estimate for the intermolecular binding energy in the solid. The electronic transition energies are calculated with TD-DFT techniques and CIS. From a detailed comparison between the molecular excitations of a single molecule and different molecular dimers in the crystal, a large fraction of the gas-to-crystal shift can be assigned to the redshift of the HOMO-LUMO excitation energy induced by the neighboring molecules in the crystal. The molecular dimers are generalized to deformed molecules, resulting in model geometries for self-trapped excitons with long radiative lifetimes related to the small transition dipole moment associated to intermolecular charge transfer ͑CT͒ transitions. The part of the Stokes shift resulting from internal deformations is obtained from TD-DFT calculations, and the self-trapping along the intermolecular distance is determined from a combination of an MP2-based intermolecular van der Waals potential with CIS for the CT transitions. After a careful elimination of the energy offsets related to the applied methods and to the lack of the complete crystalline surroundings, the calculated transition energies for the deformed dimers can be used for assigning the long-living components of the photoluminescence spectra to pairs of oppositely charged molecules and to excimer states. For the crystalline ground state, we deduce a CT transition energy of 2.14 eV along the stacking direction, significantly below previous theoretical estimates.

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Section: Influence Of Internal Deformations On Ct Transitionsmentioning

confidence: 90%

Section: Computational Schemesmentioning

confidence: 98%

Investigation of molecular dimers inα-PTCDA byab initiomethods: Binding energies, gas-to-crystal shift, and self-trapped excitons

et al. 2005

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“…At 8.2 kbar a high energy shoulder becomes visible, emerging in the 2.0 -2.1 eV region as the main peak shifts more rapidly out of this region. The most likely assignment for this shoulder is the isolated monomer transition observed as a fast decaying (~3 ns) component contributing to the high-energy wing of the 1 atm emission spectrum [7,8,14]. The monomer transition originates mainly from a PTCDA molecule within a randomized surroundings as e.g.…”

Section: Methodsmentioning

confidence: 99%

Effects of high pressure on the photoluminescence transitions of excitons in α‐PTCDA (perylene tetracarboxylic dianhydride) crystals

Tallman

Weinstein²,

DeSilva

et al. 2004

Physica Status Solidi (b)

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PACS 62.50.+p, 78.55.Kz We report investigations of the photoluminescence (PL) spectrum of α-PTCDA single crystals at 11 K and 300 K as a function of applied pressures to 54 kbar carried out using a diamond-anvil cell with annealed methanol-ethanol medium. The effects of pressure are observed on several excitonic PL features principally associated with: an excimer transition for the 300 K spectra, or an indirect Frenkel exciton and charge transfer exciton transitions (between stacked molecules in different unit cells) for the 11 K spectra. Under applied pressure, all of these features redshift at rates that are in general accord with the π -π* broadening caused by increasing overlap between PTCDA molecules, but with variations in pressure dependence, especially in the quadratic shifts, that derive from the specific character and Stokes-shift mechanisms of the exciton transitions. The observed pressure behavior conforms to a recent model of the exciton transitions in α-PTCDA based on a theoretical analysis of 1 atm time-resolved PL experiments.

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“…according to these computations PTCDA and PBI aggregates possess quite different electronic structures. 119,[122][123][124] Using the computed PES (Fig. 8) describing the intermonomer motions along RL and RT, it is possible to explain the features of both, the absorption and the emission spectrum.…”

Section: -124mentioning

confidence: 99%

The dimer-approach to characterize opto-electronic properties of and exciton trapping and diffusion in organic semiconductor aggregates and crystals

Engels

Engel

2017

Phys. Chem. Chem. Phys.

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A fundamental understanding of photo-induced processes in opto-electronic thin film devices is a prerequisite for the rational design of improved organic semiconductor materials. Absorption and emission spectra provide important insights into the complicated electronic structure of and relaxation processes in organic semiconductor aggregates and crystals. They are of interest because they often limit the efficiencies of the devices. For an assignment of the spectra a close interplay between experiment and theory is essential because simulations are often necessary to entangle the various effects which determine the features of the spectra. In the present perspective we describe the so called dimer-approach and provide a few examples in which this approach could successfully deliver an atomistic picture of photo-induced relaxation effects in perylene-based materials and characterize their optical spectra. The model Hamiltonians of standard monomer-based approaches are also briefly discussed to reveal the differences between both methods and to shed some light on their strengths and shortcomings.

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Influence of exciton transfer on the optical cycle of α-PTCDA

Cited by 11 publications

References 16 publications

Investigation of molecular dimers inα-PTCDA byab initiomethods: Binding energies, gas-to-crystal shift, and self-trapped excitons

Investigation of molecular dimers inα-PTCDA byab initiomethods: Binding energies, gas-to-crystal shift, and self-trapped excitons

Effects of high pressure on the photoluminescence transitions of excitons in α‐PTCDA (perylene tetracarboxylic dianhydride) crystals

The dimer-approach to characterize opto-electronic properties of and exciton trapping and diffusion in organic semiconductor aggregates and crystals

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