Integrating functional molecules into single-molecule devices is a key step toward the realization of future computing machines based on the smallest possible components. In this context, photoswitching molecules that can make a transition between high and low conductivity in response to light are attractive candidates. Here we present the synthesis and conductance properties of a new type of robust molecular photothermal switch based on the norbornadiene (NB)–quadricyclane (QC) system. The transport through the molecule in the ON state is dominated by a pathway through the π-conjugated system, which is no longer available when the system is switched to the OFF state. Interestingly, in the OFF state we find that the same pathway contributes only 12% to the transport properties. We attribute this observation to the strained tetrahedral geometry of the QC. These results challenge the prevailing assumption that current will simply flow through the shortest through-bond path in a molecule.

The exponential proliferation of data during the information age has required the continuous exploration of novel storage paradigms, materials, and devices with increasing data density. As a step toward the ultimate limits in data density, the development of an electrically controllable single‐molecule memristive element is reported. In this device, digital information is encoded through switching between two isomer states by applying a voltage signal to the molecular junction, and the information is read out by monitoring the electrical conductance of each isomer. The two states are cycled using an electrically controllable local‐heating mechanism for the forward reaction and catalyzed by a single charge‐transfer process for the reverse switching. This single‐molecule device can be modulated in situ, is fully reversible, and does not display stochastic switching. The I–V curves of this single‐molecule system also exhibit memristive character. These features suggest a new approach for the development of molecular switching systems and storage‐class memories.

To explore the potential of negative photochromic molecules for possible optical memory storage applications, we have here synthesized and studied a series of four norbornadiene–quadricyclane (NBD–QC) photoswitching molecules.

Development of Molecular Solar Thermal (MOST) systems for harvesting and storing solar energy is based on molecular photoswitches that undergo photoisomerizations to metastable isomers. One challenge is to achieve low-molecular weight molecules that absorb at sufficiently long wavelengths to match the solar spectrum. Here we show that this can be achieved by linking two norbornadiene (NBD) photoswitches to a central heterocycle, thiophene or carbazole, via alkyne appendages. In this approach, the same heteroaryl is used to tune the properties of two photoswitches at the same time, thereby keeping the molecular weight as low as possible. A series of NBD dimers was prepared by Sonogashira coupling reactions, and these compounds showed remarkable redshifted absorptions, with onsets of absorption as high as 468 nm, and thermal half-lives ranging from 44 seconds to 16 hours.

parallel electroless plating, [16] and shadow mask evaporation, [17,18] and the field has recently been reviewed. [19,20] Meanwhile new parallel fabrication strategies for formation of nanogap electrodes are being developed, here recent examples include mole cular crystal lithography, [21] gold nanorod alignment, [22] crack-defined electronic nanogaps, [23] self-limiting electrode growth, [24] the use of graphenebased constrictions, [25] and carbon nanotube electrodes. [26,27] A remaining challenge is scalability, that is, how to position single (or a few) molecules in the nanogap in a parallel way. In this context, an interesting approach is the use of the protodevice concept, where the single (or a few) molecule is isolated in the solution between nanoparticles, and subsequently self-assembled onto prefabricated nanoelectrodes. [28][29][30][31][32][33][34] Templated self-assembly can be used to position nanoparticles at prefabricated surfaces. Examples include positioning of gold nanoparticles and orientation of gold nanorods. [35,36] It is also possible to assemble particles using a meniscus flow over nanostructures, [37,38] chemically activate and passivate parts of a surface prior to deposition of nanoparticles, [39] making use of variations of hydrophobicity on a surface [40] or wet-contact printing. [41] Other methods involve electrostatic trapping of particles attached with molecules. [42][43][44] Here we explore the natural surface charges that different metal/metal oxides acquire in solution to guide bottom-up assembled molecular linked nanoparticle dimers to prefabricated electrodes (Figure 1). It is in this manner possible to position, isolate, and measure electron transport on a single (or a few) molecules. Electron-beam lithography (EBL) was used to fabricate electrode pairs, with optimized geometry and materials to promote the assembly of negatively charged nanoparticle dimers (Figure 2). The electrodes are made in layers of nickel (Ni) and palladium (Pd). Nickel has proven to be able to attract negatively charged citrate stabilized nanoparticles due to the positive surface potential at pH 6.5-7. [45] Pd is sandwiched between the Ni electrodes to improve the conductivity of the electrodes, and to enable an oxide free interface between the electrodes and protodevices. At the same time the top Pd layer reduces assembly of nanoparticles "on top" of the electrodes. Two different molecules, 1,6-hexanedithiol and 1,4-benzenedithiol, were used as test molecules for the construction of Single molecule electronics might be a way to add additional function to nanoscale devices and continue miniaturization beyond current state of the art. Here, a combined top-down and bottom-up strategy is employed to assemble single molecules onto prefabricated electrodes. Protodevices, which are self-assembled nanogaps composed by two gold nanoparticles linked by a single or a few molecules, are guided onto top-down prefabricated nanosized nickel electrodes with sandwiched palladium layers. It is shown that an optimized geo...

The photo- and acidochromic properties of a new generation norbornadiene derivative have been harnessed for the realization of a three-input keypad lock, where a specific sequence of inputs induces a unique output. Reversible quadricyclane/norbornadiene photoisomerization is reported, and this rare feature allows the first example of a norbornadiene-based molecular logic system. The function of this system is clearly rationalized in terms of the interconversion scheme and the absorption spectra of the involved species.

Guided deposition of nanoparticles onto different substrates is of great importance for a variety of applications such as biosensing, targeted cancer therapy, anti-bacterial coatings and single molecular electronics. It is therefore important to gain an understanding of what parameters are involved in the deposition of nanoparticles. In this work we have deposited 60 nm, negatively charged, citrate stabilized gold nanoparticles onto microstructures consisting of six different materials, (vanadium (V), silicon dioxide (SiO2), gold (Au), aluminum (Al), copper (Cu) and nickel (Ni)). The samples have then been investigated by scanning electron microscopy to extract the particle density. The surface potential was calculated from the measured surface charge density maps measured by atomic force microscopy while the samples were submerged in a KCl water solution. These values were compared with literature values of the isoelectric points (IEP) of different oxides formed on the metals in an ambient environment. According to measurements, Al had the highest surface potential followed by Ni and Cu. The same trend was observed for the nanoparticle densities. No particles were found on V, SiO2 and Au. The literature values of the IEP showed a different trend compared to the surface potential measurements concluding that IEP is not a reliable parameter for the prediction of NP deposition.

The exponential proliferation of data during the information age has required the continuous exploration of novel storage paradigms, materials, and devices with increasing data density. As a step toward the ultimate limits in data density, the development of an electrically controllable single‐molecule memristive element is reported. In this device, digital information is encoded through switching between two isomer states by applying a voltage signal to the molecular junction, and the information is read out by monitoring the electrical conductance of each isomer. The two states are cycled using an electrically controllable local‐heating mechanism for the forward reaction and catalyzed by a single charge‐transfer process for the reverse switching. This single‐molecule device can be modulated in situ, is fully reversible, and does not display stochastic switching. The I–V curves of this single‐molecule system also exhibit memristive character. These features suggest a new approach for the development of molecular switching systems and storage‐class memories.