4:00pm - 4:30pmInvited
DNA-hybrid Materials: System Integration and Electronics
Newcastle University, United Kingdom
This talk will cover the synthesis of DNA systems and their integration with electronic materials. Focus will be on the chemical and enzymatic synthesis of modified DNA to provide routes to incorporate electroactive groups at the double helix in order to examine the behaviour of DNA-hybrids as potential interconnects for molecular electronics.
The approaches covered will begin with solid-phase synthesis, explore the supramolecular assembly of templated materials and conclude with biologically powered enzymatic fabrication. In particular the enzymatic synthesis of long DNA with a controlled sequence, length and functional content will be presented. Here, a modified PCR protocol using the key components of a repeating sequence oligo-seed (ca.20 bases), the deoxynucleotide triphosphates (dNTPs), and a DNA polymerase is reported.
Incorporation of artificial nucleotides, with modifications ranging from single atom exchanges, 5-I-dCTP, 7-deaza-I-dATP, 5-Br-dUTP and 6-S-dGTP, to long chains, 5-C8-alkyne-dCTP, suggest that functional designer DNA may have applications in the production of unique conductive 1D-nanomaterials.
In a first example, 6-S-dGTP is renowned for strong metal interactions, and was exploited for the specific localisation of Au+, Ni2+, Cd2+ and Au3+ at repeating G positions as a potential route for metal-based nanowire fabrication. As the 6-S-DNA product is limited in length, an alternative thiol-modification was investigated. Using phosphorothioate dNTPs, sulfur bearing DNA products similar in length to the unmodified DNA were produced. This enabled the specific positioning of Au-nanoparticles through careful oligo-seed design.
A second example is DNA bearing the 5-C8-alkyne-dCTP, which provides alkyne anchors at sites sitting in the major groove. To demonstrate the ability to add a second layer of design, click chemistry with azide-fluor-545 was investigated. This opens up multiple routes to more complex modifications via organic synthesis at precise sites within the designer DNA for highly unique DNA-based electronic materials.
4:30pm - 5:00pmInvited
Bio-molecular Electronics Electron Transport across Peptides and Proteins
Weizmann Institute of Science, Israel
Molecular electronics has as one of its goals to incorporate functional molecules into electrical circuits, to provide characteristics beyond those of existing and predicted semiconductor-based electronics. Going from simple molecules to ones with interesting functionality is, though, a huge step. This is where proteins come in and we move to bio-molecular electronics.
Electron transport (ETp), i.e., electronic conduction across proteins in a solid state–like configuration is surprisingly efficient, and comparable to, or at times even more efficient than via completely conjugated molecules of comparable length. Working with modified proteins and homo-peptides we find that both cofactors and secondary structure matter for ETp efficiency.
An open question is if contact to the external world or, or intra-protein processes dominat transport. This is important, also for electron transfer, ET, which nature regulates via redox chemistry, i.e., injection and extraction of e-s; that is where ET and ETp are related, because the ETp analog is the coupling to the electrodes. However, for ETp a redox process is not needed, allowing its study also via non-redox proteins, such as rhodopsins and albumins (“dopable” proteins). Results point to peptides as relatively efficient transport medium. Therefore, studying transport via, and coupling to them, can be a way to learn about protein ETp and I will note also their electronic transport behaviour.
 Recent reviews of ours: N. Amdursky et al., Adv. Mater. 42,7142-7161(2014) Electronic Transport via Proteins; C. Bostick, S. Mukhopadhyay et al., submitted
* collaboration with M. Sheves & I. Pecht. Work involved/involves former group members S.Mukhopadhyay, R.Lovrincic, L.Sepunaru, Xi Yu, N.Amdursky, and present members C.Guo, J.Fereiro., and with theorists L.Kronik, P.Agrawal D.Egger, SRefaely-Abramson; with Y. Levy and Y.Gavrilov, all from the Weizmann Inst. of Science, and with J.C. Cuevas from UAM, Madrid.
5:00pm - 5:15pmOral
Molecular Diodes based on van der Waals Coupling of the Molecular Orbitals with the Electrodes
1Department of Chemistry, National University of Singapore, Singapore; 2Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore; 3Materials and Surface Science Institute and Department of Physics and Energy, University of Limerick, Co. Limerick, Ireland
The concept that certain molecules sandwiched between two electrodes may work as a molecular diode was initially proposed more than 40 years ago. To date, the fabrication of well-performing molecular diodes with rectification ratio (R) of >10 is still challenging because the chemical, supramolecular, and electronic structure of the junction, molecule-electrode coupling and electrode roughness, all affect the overall performance of the diodes and all these parameters need to be optimized. Here we show how the molecule---electrode interaction can be optimized in such a way that the molecule---electrode interaction is strong enough to achieve molecular rectification yet with the molecular frontier orbitals confined to the molecule. We formed self-assembled monolayers (SAM) of ferrocene (Fc) terminated molecules on graphene through van der Waals interactions which were then contacted with EGaIn top electrodes. Hence, the SAMs are in van der Waals contact with both electrodes. These perform well with values of R of 40. These junctions are also stable as the Fc-graphene interface, unlike the widely used unstable metal-thiolate bond, are not prone to oxidation yielding stable junctions under ambient conditions for more than 1000 cycles.
 Aviram, A.; Ratner, M. A. Chem. Phys. Lett. 1974, 29, 277.
5:15pm - 5:45pmInvited
Single-Molecule Transport in Biomolecular Structures
University of Barcelona, Spain
Electron transfer (ET) through bioorganic architectures is undoubtedly one of the most important processes in life. Millions of years of evolution have resulted in complex but fascinating biomolecular structures in living organisms that allow charge transport through organic networks with unbeatable efficiencies. Long-range ET in redox proteins involved in the respiratory chain is, among others, one of the most prominent examples of how nature has developed mechanisms to efficiently transport charge across an organized organic scaffold.
Single-molecule contacts made of a molecule covalently bridged to two metal electrodes have been shown to be experimentally realizable at room temperature. A large variety of synthetic molecular systems has been already explored bringing a robust understanding of the critical parameters required to build and measure charge transport through single-molecule devices.
In this contribution, we will present the latest applications of single-molecule junction methods with SPM approaches to study charge transport in biological architectures. The first part will describe the latest implemented methods to univocally identify the formation of single-molecule contacts between two macroscopic electrodes and characterize transport through them. Few examples on synthetic backbones will be provided to illustrate the effectiveness of the employed methodology, making emphasis on electrochemically-gated single-molecule devices with redox active molecular compounds (e.g. perylene, coronene derivatives). Next, a short overview of the state-of-the-art on single-biomolecule charge transport studies will be given, ending with our current progress on single-protein electrical contacts. During this survey, the combination of bioengineering site-directed mutagenesis procedures together with single-molecule electrical contact approaches will be shown to be an effective methodology to map the ET landscape of complex biomolecular architectures.
5:45pm - 6:15pmInvited
Gate-controlled Conductance Switching in DNA
1Arizona State University, United States; 2Northwestern University, United States
Recent advances have made it possible to design and synthesize DNA with programmable 3D nanostructures, which have stimulated efforts to study DNA as building blocks of electronic devices. Despite the advances, the electrical conductivity of native DNA cannot be regulated with an external electrical field, which prevents it from serving as an active electronic component (switch). Here we construct a molecular switch by inserting a redox group in between DNA bases. Electrically tuning of the redox group between reduced and oxidized states leads to reversible switching of the molecule between high and low conductivity states. We further show that this strategy allows tracking of single chemical reaction events, and examining of the thermodynamics and kinetics of the reaction at the single-molecule level.
6:15pm - 6:30pmOral
Quantifying Morphology-Dependent Optical Properties with Back Focal Plane Spectroscopies
University of California, Santa Barbara, United States
The propensity of organic materials to self-assemble into highly ordered structures leads to strong morphology-dependent optical properties. These optical properties, in turn, reveal important qualities of the underlying electronic excitations and have a significant impact on device performance and design. In this talk, we describe a novel class of Back Focal Plane spectroscopies that provide new insight into morphology-dependent optical properties of organic materials.
Specifically, we use Back Focal Plane imaging techniques to measure or control the momentum distribution of in-coming or out-going light rays respectively. These techniques are applied to the polymer and small-molecule materials that are deposited with distinct edge-on and face-on morphologies depending on processing conditions. Using momentum-resolved photoluminescence, we determine the orientation of transmission and absorption dipoles in these materials. We also demonstrate the use of Back Focal Plane reflectometry to perform “model-free” measurements of optical constants. The approach provides precise and accurate optical constants with quantified error estimates, obviating the complications associated with the highly model-dependent, multi-parameter spectral fitting procedures used in ellipsometry. We conclude with demonstrations of how optical anisotropies in molecular materials can be used to enhance optoelectronic processes in plasmonic and nanophotonic device architectures.