Abstract
Conductive fullerene (C60) units were designed to be arranged in one dimensional close contact by locally organizing them with covalent bonds in a spatially constrained manner. Combined molecular dynamics and quantum chemical calculations predicted that the intramolecular electronic interactions (i.e. charge transport) between the pendant C60 units could be controlled by the length of the spacers linking the C60 units and the polymer main chain. In this context, C60 side-chain polymers with high relative degrees of polymerization up to 1220 and fullerene compositions up to 53% were synthesized by ruthenium catalyzed ring-opening metathesis polymerization of the corresponding norbornene-functionalized monomers. UV/vis absorption and photothermal deflection spectra corroborated the enhanced inter-fullerene interactions along the polymer chains. The electron mobility measured for the thin film field-effect transistor devices from the polymers was more than an order of magnitude higher than that from the monomers, as a result of the stronger electronic coupling between the adjacent fullerene units within the long polymer chains. This molecular design strategy represents a general approach to the enhancement of charge transport properties of organic materials via covalent bond-based organization.
Highlights
The electronic and optoelectronic properties of organic semiconductors depend heavily on non-covalent intermolecular interactions, which result in speci c molecular arrangements, crystal packing modes, and morphology in the solid state
One way to avoid the unpredictability of non-covalent intermolecular interactions in organic semiconductors is to x the conductive components using covalent bonds
In order to investigate the effects of covalent local organization of conductive components on the optical and electronic properties, the polymer should have (i) high molecular weight (MW) in order to maximize the charge transport from intramolecular contribution, (ii) no structural and chemical defects in the repeating units, and (iii) a non-rigid backbone that ensures good solubility and allows the pendant groups to reorganize thermally for maximized intramolecular interactions
Summary
One way to avoid the unpredictability of non-covalent intermolecular interactions in organic semiconductors is to x the conductive components using covalent bonds. On a scale of several nanometers that may not be applicable to micro-scale OFETs. In order to investigate the effects of covalent local organization of conductive components on the optical and electronic properties, the polymer should have (i) high molecular weight (MW) in order to maximize the charge transport from intramolecular contribution, (ii) no structural and chemical defects in the repeating units, and (iii) a non-rigid backbone that ensures good solubility and allows the pendant groups to reorganize thermally for maximized intramolecular interactions. In addition to the better processability and thermal stability, for conductive polymers, a higher MW allows fewer hops between polymer chains and sometimes gives better connection between grains.[17,18] Good solubility is an essential property for solution-processed fabrication procedures In this context, we designed (Fig. 1) a buckminsterfullerene (C60)-containing monomer terminated with a norbornene group for ring-opening metathesis polymerization (ROMP), leading to the corresponding brush-like polymer via a “gra through” route. Given the fact that the peculiar features of C60 are retained in most of its derivatives, such arrangements would promote intramolecular fullerene interactions, which could, in turn, result in fullerene-containing materials with improved charge transport
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