Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Exciton Localization in Extended {\pi}-electron Systems: Comparison of
  Linear and Cyclic Structures   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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The categories of this paper are: nucl-ex
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The categories of this paper are: acc-phys
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The categories of this paper are: plasm-ph
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The categories of this paper are: funct-an
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The categories of this paper are: cs
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The categories of this paper are: patt-sol
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The categories of this paper are: eess
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The categories of this paper are: alg-geom
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The categories of this paper are: chao-dyn
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The categories of this paper are: mtrl-th
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The categories of this paper are: econ
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The categories of this paper are: astro-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: q-fin
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The categories of this paper are: q-bio
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The categories of this paper are: q-alg