Strategies for the Design of PEDOT Analogues Unraveled: the Use of Chalcogen Bonds and σ-Holes.

In this theoretical study, we set out to demonstrate the substitution effect of PEDOT analogues on planarity as an intrinsic indicator for electronic performance. We perform a quantum mechanical (DFT) study of PEDOT and analogous model systems and demonstrate the usefulness of the ωB97X-V functional to simulate chalcogen bonds and other noncovalent interactions. We confirm that the chalcogen bond stabilizes the planar conformation and further visualize its presence via the electrostatic potential surface. In comparison to the prevalent B3LYP, we gain 4-fold savings in computational time and simulate model systems of up to a dodecamer. Implications for design of conductive polymers can be drawn from the results, and an example for self-doped polymers is presented where modulation of the strength of the chalcogen bond plays a significant role.

Overcoming intra-molecular repulsions in PEDTT by sulphate counter-ion.

We set out to demonstrate the development of a highly conductive polymer based on poly-(3,4-ethylenedithia thiophene) (PEDTT), PEDOTs structural analogue historically notorious for structural disorder and limited conductivities. The caveat therein was previously described to lie in intra-molecular repulsions. We demonstrate how a tremendous >2600-fold improvement in conductivity and metallic features, such as magnetoconductivity can be achieved. This is achieved through a careful choice of the counter-ion (sulphate) and the use of oxidative chemical vapour deposition (oCVD). It is shown that high structural order on the molecular level was established and the formation of crystallites tens of nanometres in size was achieved. We infer that the sulphate ions therein intercalate between the polymer chains, thus forming densely packed crystals of planar molecules with extended π-systems. Consequently, room-temperature conductivities of above 1000 S cm-1 are achieved, challenging those of conventional PEDOT:PSS. The material is in the critical regime of the metal-insulator transition.

Localizing Binding Sites on Bioconjugated Hydrogen-Bonded Organic Semiconductors at the Nanoscale.

Hydrogen-bonded organic semiconductors are extraordinarily stable organic solids forming stable, large crystallites with the ability to preserve favorable electrical properties upon bioconjugation. Lately, tremendous efforts have been made to use these bioconjugated semiconductors as platforms for stable multifunctional bioelectronics devices, yet the detailed characterization of bio-active binding sites (orientation, density, etc.) at the nanoscale has not been achieved yet. The presented work investigates the bioconjugation of epindolidione and quinacridone, two representative semiconductors, with respect to their exposed amine-functionalities. Relying on the biotin-avidin lock-and-key system and applying the atomic force microscopy (AFM) derivative topography and recognition (TREC) imaging, we used activated biotin to flag crystal-faces with exposed amine functional groups. Contrary to previous studies, biotin bonds were found to be stable towards removal by autolysis. The resolution strength and clear recognition capability makes TREC-AFM a valuable tool in the investigation of bio-conjugated, hydrogen-bonded semiconductors.

Biofunctionalized conductive polymers enable efficient CO2 electroreduction.

Selective electrocatalysts are urgently needed for carbon dioxide (CO2) reduction to replace fossil fuels with renewable fuels, thereby closing the carbon cycle. To date, noble metals have achieved the best performance in energy yield and faradaic efficiency and have recently reached impressive electrical-to-chemical power conversion efficiencies. However, the scarcity of precious metals makes the search for scalable, metal-free, CO2 reduction reaction (CO2RR) catalysts all the more important. We report an all-organic, that is, metal-free, electrocatalyst that achieves impressive performance comparable to that of best-in-class Ag electrocatalysts. We hypothesized that polydopamine-a conjugated polymer whose structure incorporates hydrogen-bonded motifs found in enzymes-could offer the combination of efficient electrical conduction, together with rendered active catalytic sites, and potentially thereby enable CO2RR. Only by developing a vapor-phase polymerization of polydopamine were we able to combine the needed excellent conductivity with thin film-based processing. We achieve catalytic performance with geometric current densities of 18 mA cm-2 at 0.21 V overpotential (-0.86 V versus normal hydrogen electrode) for the electrosynthesis of C1 species (carbon monoxide and formate) with continuous 16-hour operation at >80% faradaic efficiency. Our catalyst exhibits lower overpotentials than state-of-the-art formate-selective metal electrocatalysts (for example, 0.5 V for Ag at 18 mA cm-1). The results confirm the value of exploiting hydrogen-bonded sequences as effective catalytic centers for renewable and cost-efficient industrial CO2RR applications.

Increase in electron scattering length in PEDOT:PSS by a triflic acid post-processing.

ABSTRACT: A stringent limitation in many optoelectronic devices, such as solar cells and light emitting diodes, is the intrinsic need for a transparent electrode. Uniting relevant aspects, indium tin oxide (ITO) is often the material of choice, however, alternatives are sought and being in particular found in conductive polymers. In this work, we present a novel doping strategy to arrive at highly conducting polymeric material based on poly-3,4-ethylenedioxythiophene (PEDOT). Based on commercial high conductivity PEDOT:PSS (Clevios PH 1000), and a post processing with aqueous triflic acid delivers a material that is both transparent and of low resistivity (5.23 × 10-4 Ω cm). Furthermore, this material retains its conductive character over a large temperature range, indicating metallic behaviour. This is further supported by positive magnetoconductance effects at low temperatures (1.8-10 K) and extended mean free paths of the conduction electrons are observed-evidencing for a metallic state in this polymer.

Reversible photochemical isomerization of N,N'-di(t-butoxycarbonyl)indigos.

We report on the photophysics of N,N'-di(t-butoxycarbonyl)indigos (tBOC indigos), finding that reversible photochemical trans-cis and cis-trans isomerization reactions proceed with high quantum yields (0.10-0.46). Absorption of wavelengths in the 500-600 nm region induces trans-cis isomerism, while blue light leads to the reverse cis-trans process. Like their parent indigos, trans-BOC indigos have low fluorescence yields (∼1 × 10(-3)), while the cis isomers have no measurable emission. These compounds are the first examples of photoisomerizable indigoid dyes in which photochemical isomerism effectively outcompetes radiative decay processes. Though indigo dyes typically have poor solubility in organic solvents, tBOC indigos can be dissolved at concentrations up to 8 w% in common organic solvents like acetone. Furthermore, unlike other photoisomerizable indigoids, tBOC indigos are not sensitive to quenching by proton and electron donors. These features, combined with high quantum yields of reversible photoisomerism induced by relatively low-energy photons (∼2 eV), make tBOC indigo derivatives potentially interesting for photochromic applications, such as photomechanically actuated materials.