Length-Independent Charge Transport in Chimeric Molecular Wires

Advanced molecular electronic components remain vital for the next generation of miniaturized integrated circuits. Thus, much research effort has been devoted to the discovery of lossless molecular wires, for which the charge transport rate or conductivity is not attenuated with length in the tunneling regime. Herein, we report the synthesis and electrochemical interrogation of DNA-like molecular wires. We determine that the rate of electron transfer through these constructs is independent of their length and propose a plausible mechanism to explain our findings. The reported approach holds relevance for the development of high-performance molecular electronic components and the fundamental study of charge transport phenomena in organic semiconductors

Length- and Sequence-Controlled Organic Semiconductors

Organic semiconductors have shown promise not only as alternative materials for silicon- based devices, but also as a gateway to a new paradigm of printable, biocompatible, wearable, and generally ubiquitous electronics. Considerable research effort has been devoted to elucidating structure-function relationships and charge transport phenomena in organic materials at the sub-20 nm length scale, where various key device-relevant electronic processes occur. However, the construction of precisely defined model systems at these length scales, which emulate the properties of π-stacked or single molecule organic semiconductors remains as an important unmet challenge. To address this challenge, we have developed novel methodology for constructing length- and sequence-controlled molecular wires that can self-assemble into well- defined interfaces for charge transport studies. We have characterized the electronic structure and charge transfer dynamics at these interfaces with various techniques, including electrochemistry, synchrotron-based spectroscopy, and scanning tunneling microscopy. Our findings hold broad general relevance for understanding structure-function relationships in arbitrary organic electronic materials, nanoscale charge transfer phenomena at device-relevant organic/inorganic interfaces, and electrical conductivity in biological and bioinspired systems

Synthesis of polybenzoquinolines as graphene nanoribbon precursors

The bottom-up synthesis of all-carbon graphene nanoribbons (narrow strips of sp2 hybridized carbon) has attracted much attention in recent years, with a number of contemporary demonstrations of the preparation of all-carbon systems. However, fewer studies have focused on the solution-phase synthesis of heteroatom-doped graphene nanoribbons, the preparation of which remains a significant synthetic challenge. We have developed an iterative route to oligobenzoquinolines based on the aza-Diels–Alder (Povarov) reaction and methodologies for controlling the length and sequence of our oligobenzoquinoline precursors. Our straightforward approach also provides access to crowded macromolecular polybenzoquinoline scaffolds with a unique architecture and connectivity, which are key intermediates for the preparation of nitrogen-doped nanoribbons. Our findings hold implications for the bottom-up synthesis of graphene nanoribbons whose edge character, terminal functionalities, doping, and length are precisely controllable

An Aza-Diels-Alder Route to Polyquinolines

Polyquinolines have been studied since the early 1970s due to their favorable chemical, optical, electrical, and mechanical properties. However, surprisingly few synthetic strategies have been developed for the preparation of these polymers. Herein, we demonstrate the application of the aza-DielsAlder (Povarov) reaction for the synthesis of soluble polyquinolines from a bifunctional monomer. Our approach furnishes polyquinolines with a unique architecture and connectivity in only two synthetic steps from inexpensive, commercially available reagents. The reported strategy may therefore represent a welcome addition to the polymer chemists toolkit by providing ready access to a diverse library of polyquinoline-type materialsclos

Molecular Dynamics Simulations of Perylenediimide DNA Base Surrogates.

Perylene-3,4,9,10-tetracarboxylic diimides (PTCDIs) are a well-known class of organic materials. Recently, these molecules have been incorporated within DNA as base surrogates, finding ready applications as probes of DNA structure and function. However, the assembly dynamics and kinetics of PTCDI DNA base surrogates have received little attention to date. Herein, we employ constant temperature molecular dynamics simulations to gain an improved understanding of the assembly of PTCDI dimers and trimers. We also use replica-exchange molecular dynamics simulations to elucidate the energetic landscape dictating the formation of stacked PTCDI structures. Our studies provide insight into the equilibrium configurations of multimeric PTCDIs and hold implications for the construction of DNA-inspired systems from perylene-derived organic semiconductor building blocks

An Aza-Diels-Alder Approach to Crowded Benzoquinolines

Graphene nanoribbons (GNRs) are promising candidate materials for the next generation of nanoscale electronics. Described herein is the synthesis of 2,4,6-substituted benzoquinolines, which constitute building blocks for nitrogen-doped GNRs. The presented facile and modular aza-Diels-Alder chemistry accommodates the installation of diverse functionalities at the crowded benzoquinolines 2 positions. Given the general utility of the benzoquinoline motif, these findings hold relevance not only for carbon-based electronics but also for a range of chemical disciplinesclos

Evidence for Anomalous Bond Softening and Disorder Below 2 nm Diameter in Carbon-Supported Platinum Nanoparticles from the Temperature-Dependent Peak Width of the Atomic Pair Distribution Function

X-ray pair distribution function (PDF) analysis has been applied to five carbon-supported platinum nanoparticles with sizes ranging from 1.78(2) to 11.2(2) nm. Debye (θ_D) and Einstein (θ_E) temperatures were extracted from temperature-dependent PDF peak widths. A monotonic decrease in (θ_D) with nanoparticle diameter was found and could be well explained by the effect of increased surface area except in the case of the 1.78(2) nm diameter nanoparticle where the measured Debye temperature is significantly depressed from that predicted. This suggests an anomalous bond softening in the smallest sample

Molecular Dynamics Simulations of Perylenediimide DNA Base Surrogates

Perylene-3,4,9,10-tetracarboxylic diimides (PTCDIs) are a well-known class of organic materials. Recently, these molecules have been incorporated within DNA as base surrogates, finding ready applications as probes of DNA structure and function. However, the assembly dynamics and kinetics of PTCDI DNA base surrogates have received little attention to date. Herein, we employ constant temperature molecular dynamics simulations to gain an improved understanding of the assembly of PTCDI dimers and trimers. We also use replica-exchange molecular dynamics simulations to elucidate the energetic landscape dictating the formation of stacked PTCDI structures. Our studies provide insight into the equilibrium configurations of multimeric PTCDIs and hold implications for the construction of DNA-inspired systems from perylene-derived organic semiconductor building blocks

Tailoring the Seebeck Coefficient of PEDOT:PSS by Controlling Ion Stoichiometry in Ionic Liquid Additives

Mixing simple additives into poly­(3,4-ethylenedioxythiophene)/poly­(styrenesulfonate) (PEDOT:PSS) dispersions can greatly enhance the thermoelectric properties of the cast films with little manufacturing cost, but design rules for many of these additives have yet to emerge. We show that controlling stoichiometry in ionic liquid (I.L.) additives can decouple morphological and electronic modifications to PEDOT:PSS and enhance its power factor by over 2 orders of magnitude. Blending I.L. additives with a 1:1 stoichiometry between cationic imidazolium (Im⁺) derivatives and anionic bis­(trifluoromethane)­sulfonamide (TFSI^–) groups into PEDOT:PSS dispersions raised the film conductivity to ∼1000 S/cm. The Seebeck coefficient, which gives insight into the electronic structure as well as thermoelectric performance, remained unchanged. This behavior mimics that of popular high-boiling solvent additives such as dimethyl sulfoxide and ethylene glycol, which restructure the film morphology to enhance carrier mobility. Blending I.L. additives with a 4:1 stoichiometry between Im⁺ and TFSI^– groups raises the conductivity in a similar manner but also enhances the Seebeck coefficient. This selective Seebeck enhancement proceeds from the interaction of excess Im⁺ with anionic poly­(styrenesulfonate) (PSS^–) groups, similar to previous studies using inorganic salts, that results in a shift in charge carrier populations. Inorganic salts by themselves cannot raise the conductivity of PEDOT:PSS to appropriate values since they lack the solvent restructuring effect. These I.L. additives combine the effects of high-boiling solvents and diffuse ions, with the ability to tailor the Seebeck coefficient through ion stoichiometry