1 research outputs found
Controlling Electronic Transitions in Fullerene van der Waals Aggregates via Supramolecular Assembly
Morphologies
crucially determine the optoelectronic properties of organic semiconductors.
Therefore, hierarchical and supramolecular approaches have been developed
for targeted design of supramolecular ensembles of organic semiconducting
molecules and performance improvement of, <i>e.g</i>., organic
solar cells (OSCs), organic light emitting diodes (OLEDs), and organic
field-effect transistors (OFETs). We demonstrate how the photonic
properties of fullerenes change with the formation of van der Waals
aggregates. We identified supramolecular structures with broadly tunable
absorption in the visible spectral range and demonstrated how to form
aggregates with targeted visible (vis) absorption. To control supramolecular
structure formation, we functionalized the C60-backbone with polar
(bis-polyethylene glycol malonate-MPEG) tails, thus yielding an amphiphilic
fullerene derivative that self-assembles at interfaces. Aggregates
of systematically tuned size were obtained from concentrating MPEGC60
in stearic acid matrices, while different supramolecular geometries
were provoked via different thin film preparation methods, namely
spin-casting and Langmuir–Blodgett (LB) deposition from an
air–water interface. We demonstrated that differences in molecular
orientation in LB films (<i>C</i><sub>2<i>v</i></sub> type point group aggregates) and spin-casting (stochastic
aggregates) lead to huge changes in electronic absorption spectra
due to symmetry and orientation reasons. These differences in the
supramolecular structures, causing the different photonic properties
of spin-cast and LB films, could be identified by means of quantum
chemical calculations. Employing supramolecular assembly, we propounded
that molecular symmetry in fullerene aggregates is extremely important
in controlling vis absorption to harvest photons efficiently, when
mixed with a donor molecule, thus improving active layer design and
performance of OSCs