Electronic Properties of π-conjugated Materials II - Universität ...

Oral Presentations – 2 π 2011
Modeling electronic and charge transport properties of
ambipolar and n-type organic semiconductors
F. Negri and S. Di Mo�a
Università degli Studi di Bologna, Italy
Recently synthesized quinoidal oligothiophenes have been shown to be promising materials for
their proved amphoteric properties[1], and also for their near infrared (NIR) absorption features,
driven by the reduction of their HOMO-LUMO energy gap, that make them of potential use in the
field of organic photodetectors. Here we present evidence[2] for the biradicaloid and polyenic
character of quinoidal oligothiophenes by proving at CASSCF//CASPT2 computational level the
presence of a low lying double exciton state responsible for the weak features observed in the
NIR absorption region of the longest members of this class of molecules. �e identification of
the doubly exciton state offers a unified view of the low lying electronic states for quinoidal
oligothiophenes and polyenes.
Among n-type organic semiconductors perylene bisimide (PBI) have been shown to display
promising electron mobilities. �e solid state packing and functional properties of PBIs can be
tailored by the introduction of appropriate substituents in the imide position or by core substitution
in the bay region.[3] Here we discuss charge transport properties, modeled by propagating
the charge carrier in the crystals of planar-core and core-twisted PBIs (see Figure O2.2), with
a kinetic Monte Carlo scheme. �ermally induced dynamical effects are investigated by means
of molecular dynamics simulations coupled to quantum-chemical evaluation of electronic couplings
V ij. �e study reveals that the reduced π − π stacking induced by core-twisting influences
not only static properties of the molecular material but also dynamical effects that should be
considered in the design of future organic semiconductor architectures.
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Figure O2.1 Figure O2.2