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Exciton scattering and localization in branched dendrimeric structures

Abstract

π-conjugated dendrimers are molecular examples of tree-like structures known in physics as Bethe lattices. Electronic excitations in these systems can be spatially delocalized or localized depending on the branching topology. Without a priori knowledge of the localization pattern, understanding photoexcitation dynamics reflected in experimental optical spectra is difficult. ‘Supramolecular’-like quantum-chemical calculations quickly become intractable as the molecular size increases. Here we develop a reduced exciton-scattering (ES) model, which attributes excited states to standing waves in quasi-one-dimensional structures, assuming a quasiparticle picture of optical excitations. Direct quantum-chemical calculations of branched phenylacetylene chromophores are used to verify our model and to derive relevant parameters. Complex and non-trivial delocalization patterns of photoexcitations throughout the entire molecular tree can then be universally characterized and understood using the proposed ES method, completely bypassing ‘supramolecular’ calculations. This allows accurate modelling of excited-state dynamics in arbitrary branched structures.

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Figure 1: Supramolecular dendrimers are made up via branching of linear chains.
Figure 2: Exciton-scattering patterns given by contour plots of transition density matrices from the ground state to excited states of the molecules shown in Fig. 1.

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Acknowledgements

V.Y.C. acknowledges the support through the start-up funds from WSU. The research at LANL is supported by the Center for Integrated Nanotechnology (CINT), the Center for Nonlinear Studies (CNLS) and the OBES program of the US Department of Energy. This support is gratefully acknowledged.

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Correspondence to Sergei Tretiak or Vladimir Y. Chernyak.

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Wu, C., Malinin, S., Tretiak, S. et al. Exciton scattering and localization in branched dendrimeric structures. Nature Phys 2, 631–635 (2006). https://doi.org/10.1038/nphys389

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