Frenkel exciton model of electron energy loss spectroscopy in -PTCDA

Vragović, I.; Schreiber, Michael; Scholz, Reinhard

doi:10.1016/j.jlumin.2004.08.022

Cited by 5 publications

(2 citation statements)

References 29 publications

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“…28 A model including only Frenkel excitons has allowed to quantify the anisotropic dielectric tensor, PL at low temperatures, and the dependence of electron-energyloss spectra on the momentum transfer. [20][21][22][29][30][31] Previous microscopic calculations of dielectric function and PL spectra raise the fundamental question under which conditions separate F and CT states or their mixing via electron or hole transfer determine the optical observables. In the following, we extend a Frenkel-CT approach developed earlier for a one-dimensional stack to a crystal model accounting for both basis molecules in the unit cell, combining two key ingredients applied earlier to the calculation of the anisotropic optical response of perylene compounds.…”

Section: Introductionmentioning

confidence: 99%

Crystallochromy of perylene pigments: Interference between Frenkel excitons and charge-transfer states

2009

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The optical properties of perylene-based pigments are arising from the interplay between neutral molecular excitations and charge transfer between adjacent molecules. In the crystalline phase, these excitations are coupled via electron and hole transfer, two quantities relating directly to the width of the conduction and valence band in the crystalline phase. Based on the crystal structure determined by x-ray diffraction, densityfunctional theory ͑DFT͒ and Hartree-Fock are used for the calculation of the electronic states of a dimer of stacked molecules. The resulting transfer parameters for electron and hole are used in an exciton model for the coupling between Frenkel excitons and charge-transfer states. The deformation of the positively or negatively charged molecular ions with respect to the neutral ground state is calculated with DFT and the geometry in the optically excited state is deduced from time-dependent DFT and constrained DFT. All of these deformations are interpreted in terms of the elongation of an effective internal vibration which is used subsequently in the exciton model for the crystalline phase. A comparison between the calculated dielectric function and the observed optical spectra allows to deduce the relative energetic position of Frenkel excitons and the chargetransfer state involving stack neighbors, a key parameter for various electronic and optoelectronic device applications. For five out of six perylene pigments studied in the present work, this exciton model results in excellent agreement between calculated and observed optical properties.

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Section: Introductionmentioning

confidence: 99%

Crystallochromy of perylene pigments: Interference between Frenkel excitons and charge-transfer states

2009

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“…Therefore, to attain high quantum efficiencies suitable for successful technological implementation, the luminescence behavior of these crystalline materials needs to be controlled requiring an understanding of the excited states in the solid-state phase. Accordingly, widespread theoretical and experimental attention has been focused on the mechanism of the electronic excitations in organic solids, predominantly described by Frenkel excitons as a superposition of localized excitations. − Throughout the years, researchers have utilized the simple model developed over six decades ago by Kasha and co-workers , to understand the photophysics of dimers, as such, molecular dimers stacked in a “side-by-side” fashion result in a positive Coulomb coupling and exhibit a blue-shifted absorption maximum accompanied with a suppressed radiative decay rate and are known as H-aggregates, whereas those packed in a “head-to-tail” configuration exhibit a negative Coulomb coupling leading to a red-shifted absorption maximum and enhanced radiative decay rate and are referred as J-aggregates . One can shift between H- and J-aggregations through altering the slip or angle between the molecules, and accordingly, many groups have utilized this strategy to generate H- or J-aggregated structures. , It is important to note that the difference in the photoluminescence between H- and J-aggregates is related to the radiative decay rates but not to the total emission quantum yield.…”

Section: Introductionmentioning

confidence: 99%

Bright Frenkel Excitons in Molecular Crystals: A Survey

2021

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We computed the optical properties of a large set of molecular crystals (∼2200 structures) composed of molecules whose lowest excited states are strongly coupled and generate wide excitonic bands. Such bands are classified in terms of their dimensionality (1-, 2-, and 3-dimensional), the position of the optically allowed state in relation with the excitonic density of states, and the presence of Davydov splitting. The survey confirms that one-dimensional aggregates are rare in molecular crystals highlighting the need to go beyond the simple low-dimensional models. Furthermore, this large set of data is used to search for technologically interesting and less common properties. For instance, we considered the largest excitonic bandwidth that is achievable within known molecular crystals and identified materials with strong super-radiant states. Finally, we explored the possibility that strong excitonic coupling can be used to generate emissive states in the near-infrared region in materials formed by molecules with bright visible absorption and we could identify the maximum allowable red shift in this material class. These insights with the associated searchable database provide practical guidelines for designing materials with interesting optical properties.

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Dispersion of electron–hole excitations in pentacene along (100)

Knupfer

Berger

2006

Chemical Physics

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Frenkel exciton model of electron energy loss spectroscopy in -PTCDA

Cited by 5 publications

References 29 publications

Crystallochromy of perylene pigments: Interference between Frenkel excitons and charge-transfer states

Crystallochromy of perylene pigments: Interference between Frenkel excitons and charge-transfer states

Bright Frenkel Excitons in Molecular Crystals: A Survey

Dispersion of electron–hole excitations in pentacene along (100)

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