Exciton Localization in Extended {\pi}-electron Systems: Comparison of Linear and Cyclic Structures

Alexander Thiessen; Dominik Würsch; Stefan-S. Jester; A. Vikas Aggarwal; Alissa Idelson; Sebastian Bange; Jan Vogelsang; Sigurd Höger; John M. Lupton

arXiv · 1506.05522

Exciton Localization in Extended {\pi}-electron Systems: Comparison of Linear and Cyclic Structures

Alexander Thiessen·Dominik Würsch·Stefan-S. Jester·A. Vikas Aggarwal·Alissa Idelson·Sebastian Bange·Jan Vogelsang·Sigurd Höger·John M. Lupton

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Abstract

We employ five {\pi}-conjugated model materials of different molecular shape --- oligomers and cyclic structures --- to investigate the extent of exciton self-trapping and torsional motion of the molecular framework following optical excitation. Our studies combine steady-state and transient fluorescence spectroscopy in the ensemble with measurements of polarization anisotropy on single molecules, supported by Monte Carlo simulations. The dimer exhibits a significant spectral red-shift within $\sim$ 100 ps after photoexcitation which is attributed to torsional relaxation. This relaxation mechanism is inhibited in the structurally rigid macrocyclic analogue. However, both systems show a high degree of exciton localization but with very different consequences: while in the macrocycle the exciton localizes randomly on different parts of the ring, scrambling polarization memory, in the dimer, localization leads to a deterministic exciton position with luminescence characteristics of a dipole. Monte Carlo simulations allow us to quantify the structural difference between the emitting and absorbing units of the {\pi}-conjugated system in terms of disorder parameters.

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Alexander Thiessen, Dominik Würsch, Stefan-S. Jester, A. Vikas Aggarwal, Alissa Idelson, Sebastian Bange, Jan Vogelsang, Sigurd Höger, John M. Lupton. 2015-06-18. Exciton Localization in Extended {\pi}-electron Systems: Comparison of Linear and Cyclic Structures. https://arxiv.org/abs/1506.05522

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