Efficient Exciton Diffusion and Resonance-Energy Transfer
in Multilayered Organic Epitaxial Nanofibers
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Abstract
Multilayered epitaxial nanofibers
are exemplary model systems for
the study of exciton dynamics and lasing in organic materials because
of their well-defined morphology, high luminescence efficiencies,
and color tunability. We use temperature-dependent continuous wave
and picosecond photoluminescence (PL) spectroscopy to quantify exciton
diffusion and resonance-energy transfer (RET) processes in multilayered
nanofibers consisting of alternating layers of para-hexaphenyl (p6P)
and α-sexithiophene (6T) serving as exciton donor and acceptor
material, respectively. The high probability for RET processes is
confirmed by quantum chemical calculations. The activation energy
for exciton diffusion in p6P is determined to be as low as 19 meV,
proving p6P epitaxial layers also as a very suitable donor material
system. The small activation energy for exciton diffusion of the p6P
donor material, the inferred high p6P-to-6T resonance-energy-transfer
efficiency, and the observed weak PL temperature dependence of the
6T acceptor material together result in an exceptionally high optical
emission performance of this all-organic material system, thus making
it well suited, for example, for organic light-emitting devices