Chemical doping enhances electronic transport in networks of hexabenzocoronenes assembled in non-aqueous electrolyte

Abstract

The charge-transporting ability of supramolecular polymer networks assembled from hexabenzocoronenes (HBCs) in nonaqueous electrolyte is reported here for the first time. Enhanced electronic conductivity is observed when the HBC subunits are chemically oxidized to radical cations, which is rationalized using density functional theory.Organic semiconductors with tunable, well-behaved charge transport have led to exciting advances for a broad range of (opto)electronic, photovoltaic and sensing technologies. 1 Recent work further highlights opportunities to integrate these materials in electrochemical devices. 2 Along these lines, we were interested in understanding their charge-transporting properties in electrolytes, toward flowable electrodes 3 with both ion and electron transport ability. Here, the electrolyte carries the ion current and the embedded organic semiconductor can be triggered, by some chemical or electrochemical means, to transport the electrons (or holes). For comparison, carbon nanomaterials with metallic or semi-metallic character confer static electronic conductivity when dispersed in electrolyte, but also improves when their loading exceeds a percolation threshold, indicating 3-D network formation is critical. 4 Notably, these nanomaterials are compositionally heterogeneous and offer limited means of tuning network conductivity and architecture through molecular engineering. 5 We hypothesized that supramolecular polymers of polycyclic aromatic hydrocarbons 6 (PAHs) would provide an attractive platform with modular tunability (Fig. 1). Achieving success in this regard would depend on the ability of these materials to assemble into nanowires and networks in electrolyte and, furthermore, be induced to transport charge (e.g., via a hopping mechanism 7 ). Here, we show that a new hexa-peri-hexabenzocoronene (HBC) assembles in non-aqueous electrolyte, and achieves mixed ion-and electronic-conductivity when HBC radical cations are introduced to the assembly (Fig. 1B). Up to 20-fold gains in shuttling current are demonstrated for HBC/HBC •+ mixed nanowire assemblies compared to assemblies of undoped HBC. We rationalize this behaviour using density functional theory (DFT), which supports a highly delocalized Fig. 1 Schematic representation of HBC assembly into supramolecular networks in liquid electrolyte (A) and subsequent chemical doping by HBC radical cations, which enhance the electronic charge transporting ability of the network (B). † Electronic supplementary information (ESI) available: Synthesis and characterization of all compounds, computational details, experimental details for optical spectroscopy, X-ray spectroscopy, EPR spectroscopy, and electrochemical measurements. See

Supramolecular Perylene Bisimide-Polysulfide Gel Networks as Nanostructured Redox Mediators in Dissolved Polysulfide Lithium–Sulfur Batteries

“…The mechanism of charge transport through self-assembled nanofibers is under further investigation; however, we hypothesize that rapid self-exchange of electrons through π-stacks of PBI nanowires, as has been previously reported, is partially responsible for the increased current. Related self-assembled nanowires of π-stacked hexabenzocornonenes have also shown enhanced solution-state electron transport when chemically doped …”

“…Related self-assembled nanowires of πstacked hexabenzocornonenes have also shown enhanced solution-state electron transport when chemically doped. 60 Having successfully demonstrated our proof of concept for a charge-transporting PBI redox mediator network, improved rate performance was further achieved by including conductive carbon cloth (C-cloth) with the dissolved PBI-PS gel catholyte. By analogy to biological vasculature, charge transport in these cells propagates through both "arteries" and "capillaries": that is to say, current travels from the electrode surface through the 8 μm diameter C-cloth arteries and then is locally distributed to PS by the nanoscale PBI capillary network.…”