Experimental and theoretical studies of the electronic transport of an extended curcuminoid in graphene nano-junctions.

Exploiting the potential of curcuminoids (CCMoids) as molecular platforms, a new 3.53 nm extended system (pyACCMoid, 2) has been designed in two steps by reacting a CCMoid with amino-terminal groups (NH2-CCMoid, 1, of 1.79 nm length) with polycyclic aromatic hydrocarbon (PAH) aldehydes. CCMoid 2 contains pyrene units at both ends as anchoring groups to optimize its trapping in graphene nano-junctions created by feedback-controlled electro-burning. The measured I-V characteristics show gate-dependent behaviour at room temperature and 10 K, with increased conductance values compared to shorter CCMoids previously reported, and in agreement with DFT calculations. Our results show that the adjusted molecular design improves the conductance, as system 2 separates the conductive backbone from the anchor groups, which tend to adopt a planar configuration upon contact with the graphene electrodes. DFT calculations using Green functions of a set of different molecular conformations of 2 on graphene electrodes show a direct relationship between the units (e.g. pyrene, amide, etc.), in the molecule, through which electrons are injected and the conductance values; where the size of the spacing between the graphene electrodes contributes but is not the dominant factor, and thus, counter-intuitively the smallest spacing gives one of the lowest conductance values.

Dielectric behavior of curcuminoid polymorphs on different substrates by direct soft vacuum deposition.

Our work examines the structural-electronic correlation of a new curcuminoid, AlkCCMoid, as a dielectric material on different substrates. For this purpose, we show a homemade sublimation method that allows the direct deposition of molecules on any type of matrix. The electronic properties of AlkCCMoid have been evaluated by measurements on single crystals, microcrystalline powder, and sublimated samples, respectively. GIWAXS studies on surfaces and XRD studies on powder have revealed the existence of polymorphs and the effect that substrates have on curcuminoid organization. We describe the dielectric nature of our system and identify how different polymorphs can affect electronic parameters such as permittivity, all corroborated by DFT calculations.

Emergent Insulator-Metal Transition with Tunable Optical and Electrical Gap in Thin Films of a Molecular Conducting Composite.

Composites exhibit unique synergistic properties emerging when components with different properties are combined. The tuning of the energy bandgap in the electronic structure of the material allows designing tailor-made systems with desirable mechanical, electrical, optical, and/or thermal properties. Here, we study an emergent insulator-metal transition at room temperature in bilayered (BL) thin-films comprised of polycarbonate/molecular-metal composites. Temperature-dependent resistance measurements allow monitoring of the electrical bandgap, which is in agreement with the optical bandgap extracted by optical absorption spectroscopy. The semiconductor-like properties of BL films, made with bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF or ET) α-ET2I3 (nano)microcrystals as two-dimensional molecular conductor on one side and insulator polycarbonate as a second ingredient, are attributed to an emergent phenomenon equivalent to the transition from an insulator to a metal. This made it possible to obtain semiconducting BL films with tunable electrical/optical bandgaps ranging from 0 to 2.9 eV. A remarkable aspect is the similarity close to room temperature of the thermal and mechanical properties of both composite components, making these materials ideal candidates to fabricate flexible and soft sensors for stress, pressure, and temperature aiming at applications in wearable human health care and bioelectronics.