Stark Effect of Intrinsic and Extrinsic Charge-Transfer Excitons in a Linear Donor−Acceptor Stack: Anthracene−Pyromellitic Dianhydride

Abstract

Anthracene-PMDA single crystals display at 2K about 70 meV below a well-known intrinsic charge-transfer exciton three narrow absorption lines, which are attributed to CT excitons bound to defects of a few 10(-5) concentration. All excitons respond very sensitively to electric fields along the molecular stack because of the large dipole moment, about 2 eA, of an ionized donor-acceptor pair, but only intrinsic excitons observe an optical selection rule. Although the triclinic unit cell contains only one pair of molecules, excitons appear in field-modulated spectra as near-degenerate doublets of different parity with very small splitting. The line shape of the EA spectra and selection rules with respect to the polarization of light and orientation of the field are consistent with the inversion symmetry of the lattice and the molecules. The simple crystal structure enables identification of the defects that are responsible for extrinsic excitons. Symmetry consideration based on translation invariance lead to a new interpretation of intrinsic excitons as true crystal states with charge transfer from the donor to the acceptor sublattice.

Probing Fabry–Perot Interference in Self-Assembled Excitonic Microcrystals with Subgap Light Emission

“…A discernible peak centered at 540 nm appears on top of the rising background. Based on previous studies, we assign this peak as the CT exciton resonance. , It is denoted explicitly in Figure .…”

“…In this study, we examine the characteristics and formation mechanism of Fabry–Perot interference fringes in the suboptical gap light emission spectra of the perovskite-like layered material hexyl ammonium lead iodide (HA 2 PbI 4 ) and 1:1 cocrystals of anthracene and pyromellitic dianhydride (A-PMDA). The ability to process semiconducting hybrid organic–inorganic perovskite in solution gives them the potential to transform methods to fabricate optoelectronic technologies including photovoltaic cells, ,,, light-emitting diodes, ,, and lasers. ,, A-PMDA has long been used as a model system to understand the properties of charge-transfer (CT) excitons including fine structure and their coupling to material vibrations. − The ability to reliably control the light emitted by this material may open interesting avenues to interrogate intermolecular interactions in the solid state.…”

Insight into Intermolecular Charge Transfer Determined by Two Packing Mode Cocrystals

“…For these D–A systems, many works have been carried out to capture the CT intermediates and obtained some information about the dynamic processes by means of time-resolved transient absorption, , emission, , Raman, − and other techniques, so as to further understand the nature of CT state. The intermolecular CT between the electron donor and electron acceptor in solution has been studied and reported a lot. , However, the electronic interactions between the donor and acceptor in the cocrystals are not deeply explored because of the technical limitations. − However, it is a big challenge to characterize and explore the excited states of solid state because there are multiple influence factors to the properties of excited state of solid state, such as intermolecular CT, hydrogen bond, π–π stacking, van der Waals force, and so forth. The motivation here is that we want to explore the excited states and its dynamics in the solid state by ultrafast time-resolved spectroscopy.…”

Charge transfer excitons in a donor–acceptor amphidynamic crystal: the role of dipole orientational order

“…34 Moreover, energetically distinct CTE transitions have been observed only in the presence of an external electric field in Stark effect experiments at cryogenic temperatures. 35,36 The explanation for such pioneering experiments resides in the breaking of the centrosymmetric charge distribution of the CTE configuration, which can be D(+)A(À)D or DA(À)D(+) with equal probability. In the presence of an electric field in the stacking direction, the resulting parallel or antiparallel CTE orientations separate at different energies.…”