Exciton–Exciton Annihilation Is Coherently Suppressed in H-Aggregates, but Not in J-Aggregates

Abstract

We theoretically demonstrate a strong dependence of the annihilation rate between (singlet) excitons on the sign of dipole–dipole couplings between molecules. For molecular H-aggregates, where this sign is positive, the phase relation of the delocalized two-exciton wave functions causes a destructive interference in the annihilation probability. For J-aggregates, where this sign is negative, the interference is constructive instead; as a result, no such coherent suppression of the annihilation rate occurs. As a consequence, room temperature annihilation rates of typical H- and J-aggregates differ by a factor of ∼3, while an order of magnitude difference is found for low-temperature aggregates with a low degree of disorder. These findings, which explain experimental observations, reveal a fundamental principle underlying exciton–exciton annihilation, with major implications for technological devices and experimental studies involving high excitation densities.

Enhanced Energy Transfer in Doped Bifluorene Single Crystals: Prospects for Organic Lasers

“…To optimize molecular design for the energy transfer process, one must consider intramolecular as well as intermolecular properties. Exciton transport in highly ordered molecular crystals is determined by relative orientation of dipole moments leading to constructive/destructive interference in J‐/H‐type excitonic coupling . At the same time excitonic coupling is highly sensitive to static and dynamic disorder, hence molecular rigidity plays a role in exciton transport .…”

“…Exciton transport in highly ordered molecular crystals is determined by relative orientation of dipole moments leading to constructive/destructive interference in J-/H-type excitonic coupling. [26] At the same time excitonic coupling is highly sensitive to static and dynamic disorder, hence molecular rigidity plays a role in exciton transport. [44] Later stage of host-dopant FRET is controlled by spectral overlap, host photoluminescence (PL) quantum yield and dipole-dipole orientation factor.…”

“…The former results in low radiative rate and close π–π stacking leads to formation of trap states (i.e., excimers) . The latter introduces strong reabsorption losses in crystals, while enhanced exciton transport results in significant exciton annihilation losses . Recent studies show that the effects of long‐range Coulomb coupling could be compensated by short‐range charge transfer interactions in crystals with dense molecular packing (<4 Å), enabling superior charge mobility and emission efficiency in single component crystals .…”

Mapping of exciton–exciton annihilation in a molecular dimer via fifth-order femtosecond two-dimensional spectroscopy

“…We note that, for dimers and degenerate levels E fg = Eee, the annihilation rate is similar for H-and J-aggregates. 56 The parameters entering into the dimer Hamiltonian are summarized in Table I. These are the monomer energies and the couplings J, K, and L. Also given is a value for the relaxation rate kM for the |e⟩ ← | f ⟩ monomer transition.…”

Double-excitation manifold's effect on exciton transfer dynamics and the efficiency of coherent light harvesting

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