4.10.2017

Jun.-Prof. Dr. Katharina Broch (Eberhard Karls Universität Tübingen, Německo):
Tuning of charge transfer in pentacene: Impact on Davydov-splitting and singlet fission time constants

Abstract:

As the spin-allowed photophysical process converting an excited singlet state
into two triplet states, singlet fission has attracted significant attention
for device applications. Research so far has focused mainly on the
understanding of singlet fission in pure materials, yet blends offer the
premise of a controlled tuning of the intermolecular interactions with
potential impact on singlet fission efficiencies. I am going to present some
results of a recent study on mixtures of pentacene (PEN) with non-interacting
spacer molecules. Comparison of experimentally determined steady state optical
properties and theoretical calculations indicates a reduction of
charge-transfer interactions between neighboring PEN molecules with increasing
fraction of spacer molecules. This weaker charge-transfer coupling is
theoretically predicted to slow down singlet fission in these blends, but
surprisingly even in those mixed films singlet fission occurs on a timescale
comparable to that in pure pentacene (~ 100 fs). The observed robustness of
singlet fission in such mixed films can be explained by a mechanism of exciton
diffusion to hot spots with closer intermolecular spacings.