Perylene-3,4,9,10-tetracarboxylic diimide (PDI) has emerged as a building block of organic materials for next generation molecular electronics. Intensely absorbing and chemically robust, PDI-based materials often excel as n-type semiconductors in organic field-effect transistors and organic photovoltaic (OPV) cells. Notably, twistacene nanoribbons arising from the iterative fusion of PDI to ethylene have been incorporated into OPV cells with power conversion efficiencies approaching 10%. These PDI-twistacenes adopt various unresolvable isoenergetic conformations in solution, precluding the possibility of optical activity. In pursuit of persistent helical chirality in PDI-based nanoribbons, I have prepared and now present naphthyl- and anthracenyl-linked PDI-dimer helicene (NPDH and APDH). Their syntheses entail the cross-coupling of an acene to two PDI subunits, followed by oxidative ultraviolet cyclizations. Straining the polyaromatic surface does not encumber the efficiency of these photocyclizations: they proceed quantitatively, without a trace of the sterically favored regioisomers. We have resolved NPDH and APDH into their constituent enantiomers by chiral high performance liquid chromatography. Solutions of APDH racemize at room temperature, whereas NPDH does not invert at 250 °C. The enantiostability of NPDH arises from the extensive intramolecular overlap of its π-surface. Looking down its stereogenic axis reveals ten pairs of π-bonded atoms eclipse one another. The nearest of these pairs are separated by 3.2 Å, closer than twice the van der Waals radius of the carbon atom. Thus, the naphthyl link of NPDH facilitates intramolecular π-to-π collisions between the PDI subunits. Voltammetric, spectroelectrochemical, and EPR measurements suggest these π-to-π collisions enable through-space electronic delocalization when NPDH is reduced. I next report the preparation of a π-helix of helicenes constituted from three PDI monomers and two naphthalene subunits. Two different synthetic routes of alternating cross-couplings and oxidative photocyclizations provided this nanoribbon, naphthyl-fused PDI-trimer helix (NP3H). Remarkably, visible light from household lightbulbs induces these cyclizations, although the final cyclization proceeds more swiftly when on the helix exterior than when within its core. NP3H possesses extraordinary chiroptical properties, exhibiting numerous and incredibly intense electronic circular dichroism (ECD) across the UV-visible range (|Δε| = 820 M-1 cm-1 at 407 nm). The ECD spectrum of NP3H transforms significantly in the presence of a mild reducing agent and visible light. Spectroelectrochemical measurements confirmed that photoinduced electron transfer to the π-helix tunes its absorbance of circularly polarized light.

No description available.

Thesis (Ph.D.)--Physics, Georgia Institute of Technology, 2008. / Committee Chair: Alexei Marchenkov; Committee Member: Bruno Frazier; Committee Member: Dragomir Davidovic; Committee Member: Markus Kindermann; Committee Member: Phillip First

Thesis (M.S.)--OGI School of Science & Engineering at OHSU, 2005. / Includes bibliographical references (leaves 59-61).

In molecular electronics, the building material (traditionally elemental semiconductor) is replaced by single molecules or a nanoscale collection of molecules. Key to molecular electronics is the ability to precisely embed molecules into a nano device/structure and to manipulate large numbers of functional devices so they can be built in parallel, with each nano-device precisely located on the electrodes. In this work, the assembly of organic and inorganic nanostructures dispersed in aqueous solutions has been controlled via chemical functionalisation. By combining this bottom-up assembly strategy with traditional top-down lithographic apporaches, the properties of these nanostructures have been investigated via a range of different techniques. The high degree of control on the molecular design through chemical synthesis and the scalability by self-assembly make this approach of interest in the field of molecular electronics. In this regard, this dissertation presents a solution-based assembly method for producing molecular transport junctions employing metallic single-walled carbon nanotubes as nanoelectrodes. On solid substrates, electrical and electronic properties have been investigated by Conducting Atomic Force Microscopy (C-AFM). Furthermore, different strategies for asymmetric junction formation have been explored towards the development of a potential nanoscale Schottky diode. Moreover, various patterning techniques based on shadow evaporation and AFM probe scratching have been investigated for the assembly of 1-D nanostructures. Nanostructures dispersed in solution were organised onto surfaces by means of dielectrophoretic assembly, and their electronic properties was then measured by the means of a probing station. In addition to the aforementioned organic nanostructures, we also report on the dispersion of boron nitride nanotubes (BNNT) by DNA wrapping, followed by the formation of nano-hybrids of boron nitride nanotubes and carbon nanotubes. Previously, researchers have adopted BNNT as a 2D dielectric layer. The work inspires me to adopt boron nitride nanotubes as 1D dielectric materials. The techniques developed in this thesis are of interest for fundamental studies of electron transport in molecules and nanostructures. Addtionally, the approaches developed in this work may facilitate the advancement of new technologies for electronics, including, but not limited to, future circuits based on single-wall carbon/boron nitride nanotubes with specific functionality.

HTML clipboardIn this thesis, dynamic effects on electron transport in molecular electronic devices are presented. Special attention is paid to the dynamics of atomic motions of bridged molecules, thermal motions of surrounding solvents, and many-body electron correlations in molecular junctions. In the framework of single-body Green’s function, the effect of nuclear motions on electron transport in molecular junctions is introduced on the basis of Born-Oppenheimer approximation. Contributions to electron transport from electron-vibration coupling are investigated from the second derivative of current-voltage characteristics, in which each peak is corresponding to a normal mode of the vibration. The inelastic-tunneling spectrum is thus a useful tool in probing the molecular conformations in molecular junctions. By taking account of the many-body interaction between electrons in the scattering region, both time-independent and time-dependent many-body Green’s function formula based on timedependent density functional theory have been developed, in which the concept of state of the system is used to provide insight into the correlation effect on electron transport in molecular devices. An effective approach that combines molecular dynamics simulations and first principles calculations has also been developed to study the statistical behavior of electron transport in electro-chemically gated molecular junctions. The effect of thermal motions of polar water molecules on electron transport at different temperatures has been found to be closely related to the temperature-dependent dynamical hydrogen bond network. / QC20100630

DNA molecules possess high density genetic information in living beings, as well as selfassembly and self-recognition properties that make them excellent candidates for many scientific areas, from medicine to nanotechnology. The process of electron transport through DNA is important because DNA repair occurs spontaneously via the process that restores mismatches and lesions, and furthermore, DNA-based molecular electronics in nano-bioelectronics can be possible through the process. In this thesis, we study theoretically the transport properties through a one-dimensional one-channel DNA model, a quasi-one-dimensional one-channel DNA model, and a two-dimensional four-channel DNA model by using the Tight-Binding Hamiltonian method. We show graphical outputs of the transmission, overall contour plots of transmission, localization lengths, the Lyapunov exponent, and current-voltage characteristics as a function of incoming electron energy and magnetic flux which are obtained using Mathematica run on the CSH Beowulf Cluster. Our results show that the semiconductor behavior can be observed in the I-V characteristics. The current through a quasi-one-dimensional one-channel DNA model starts to flow after the breakdown voltage and remains constant after threshold voltage. The variations of the temperature make the fluctuations of the system. As the temperature increases, the sharp transmission resonances are smeared out and the localization lengths are also decreased. Due to a magnetic field penetrating at the center of the two-dimensional DNA model, the Aharonov- Bohm (AB) oscillations can be observed. / Sequence dependent electron transport through a one-dimensional, one-channel DNA model -- Backbone-induced effects on charge transport through a quasi one-dimensional DNA molecule -- Temperature and magnetic fields effects on the electron transport through two-dimensional and four-channel DNA model.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: molecular electronics; triplet-triplet; singlet-singlet; energy transfer. Includes bibliographical references (p. 88-92).

No description available.

The field of structural DNA nanotechnology utilizes DNA's powerful base-pairing molecular recognition criteria to help solve real challenges facing researchers in material science and nanotechnology, some of which include synthesis, sensing, catalysis, delivery, storage, optics, electronics, and scaffolding. In it, DNA is stripped away from any of its preconceived biological roles, and is treated as a powerful synthetic polymer. A subarea of research that our group has recently termed supramolecular DNA nanotechnology is emerging, and is proving to be a powerful complement to some of the already established rules of structural DNA nanotechnology. The work within this thesis falls under the umbrella of supramolecular DNA nanotechnology, and can conceptually be divided into three parts. (1) The first deals with the problem of discrete nanopartic1e organization. In it we present an approach for the facile and economical access to libraries of discrete nanoparticle assemblies that are addressable and switchable post-assembly. (2) The second deals with the synthesis of three-dimensional DNA assemblies. In it we present an approach for the facile construction of discrete three-dimensional DNA cages that can be structurally oscillated between pre-defined lengths, and adapt this approach to generate geometrically well-defined DNA columns of modular stiffness. (3) The last part deals with the use of small molecules to reprogram the assembly behavior of DNA. In it we use molecules to address the issue of error-correction, during and after the assembly process, and to facilitate the synthesis of "higher-order" DNA helices composed of more than two DNA strands. This work collectively offers a set of simple solutions to some of the bigger challenges currently facing researchers in DNA nanotechnology, and provides a snapshot of what is to be expected from tehe emerging discipline that is supramolecular DNA nanotechnology.