Electrochemical Deposition of a Single‐Crystalline Nanorod Polycyclic Aromatic Hydrocarbon Film with Efficient Charge and Exciton Transport

Abstract

Electrochemical deposition has emerged as an efficient technique for preparing conjugated polymer films on electrodes. However, this method encounters difficulties in synthesizing crystalline products and controlling their orientation on electrodes. Here we report electrochemical film deposition of a large polycyclic aromatic hydrocarbon. The film is composed of single‐crystalline nanorods, in which the molecules adopt a cofacial stacking arrangement along the π–π direction. Film thickness and crystal size can be controlled by electrochemical conditions such as scan rate and electrolyte species, while the choice of anode material determines crystal orientation. The film supports exceptionally efficient migration of both free carriers and excitons: the free carrier mobility reaches over 30 cm2 V−1 s−1, whereas the excitons are delocalized with a low binding energy of 118.5 meV and a remarkable exciton diffusion length of 45 nm.

Electron transfer in polyaromatic hydrocarbons and molecular carbon nanostructures

“…Furthermore, as observed in some works concerning the organic semiconductors and their electrochemical synthesis, as also reported by Bruno et al [37], the oligomerization process leads to an apparent narrowing of the solvent potential window at negative values [37]. The authors proposed that the proton released in the proximity of the electrode during the oligomerization process, coordinated by two CH 2 Cl 2 molecules would in fact undergo a reduction process at a potential of - also observed the formation of a conductive film on the ITO electrode, which was attributed to the self-assembling of HBC molecules in fiber-like structures, due to the lower solubility of HBC molecules and intermolecular π-π interactions, even with a graphene monolayer surface influencing the crystal growth orientation [66].…”

Nanographenes and Graphene Nanoribbons as Multitalents of Present and Future Materials Science

“…Of widespread current use is a “polymerization–graphitization” protocol, in which branched polyphenylenes are made in a first step and then subjected to a chemical cyclodehydrogenation. Now the scope of cyclodehydrogenation is further broadened by the recent success of electrochemical methods. , The branched polyphenylenes serve as carbon reservoirs; therefore, their topologies are crucial since the flattening process should neither leave holes of partially dehydrogenated spots nor produce spatial overlap of benzene rings. Scheme presents some precursor polymers which document both the importance of a multibenzene “Lego” and the need for high molecular weights in the precursors. − Transition-metal-catalyzed polycondensations, as demonstrated in Scheme b–c, suffer from unavoidable loss of functional groups, − thus disturbing the perfect stoichiometries required for polycondensation and limiting the molecular weights, while repetitive Diels–Alder cycloadditions according to Scheme d can provide the targeted lengths of the polymers.…”

“…Now the scope of cyclodehydrogenation is further broadened by the recent success of electrochemical methods. 50,51 The branched polyphenylenes serve as carbon reservoirs; therefore, their topologies are crucial since the flattening process should neither leave holes of partially dehydrogenated spots nor produce spatial overlap of benzene rings. Scheme 2 presents some precursor polymers which document both the importance of a multibenzene "Lego" and the need for high molecular weights in the precursors.…”

Coatable Negative Dispersion Retarder: Kinetically Controlled Self-Assembly Pathway of Butterfly-Shaped Molecular Building Blocks for the Construction of Nanocolumns

“…Specifically, discotic molecules with π-conjugated aromatic cores assemble into the columnar phase that generates delocalized π-states by overlapping p-orbitals. − However, while calamitic LCs have already contributed to large-area displays, achieving the anisotropic property of discotic LCs has proven difficult mainly due to their high transition temperature, aggregation tendency, and low processability. These are a consequence of bulky discotic aromatic core, which allows for an increase in transition temperature by strong intermolecular cohesion with π–π stacking. − Therefore, many researchers have designed and investigated versatile small molecules such as hockey sticks or rod-disc molecules to induce the columnar LC phase with high mobility at low temperatures. − Especially, the Ungar, Percec, and Cheng research groups have produced a notable new concept involving incorporation of directional hydrogen bonding in a molecule, producing columnar phases even by calamitic, conical, or hemispherical molecules. − …”