Academic literature on the topic 'Nanoring'

When light is absorbed by a nanoring consisting of 6–24 porphyrin units, the excitation delocalizes over the whole molecule within 200 fs. Highly symmetric nanorings exhibit thermally enhanced super-radiance.

We report strong plasmon–exciton coupling in bimetallic nanorings and nanocuboids, and demonstrate nanoring possesses larger enhanced electric field distribution, which enables to couple with more excitons, resulting to a larger Rabi splitting.

The fact that structural RNA motifs can direct RNAs to fold and self-assemble into predictable pre-defined structures is an attractive quality and driving force for RNA’s use in nanotechnology. RNA’s recognized diversity concerning cellular and synthetically selected functionalities, however, help explain why it continues to draw attention for new nano-applications. Herein, we report the modification of a bifurcated reporter system based on the previously documented Spinach aptamer/DFHBI fluorophore pair that affords the ability to confirm the assembly of contiguous RNA strands within the context of the previously reported multi-stranded RNA nanoring. Exploration of the sequence space associated with the base pairs flanking the aptamer core demonstrate that fluorescent feedback can be optimized to minimize the fluorescence associated with partially-assembled RNA nanorings. Finally, we demonstrate that the aptamer-integrated nanoring is capable of assembling directly from transcribed DNA in one pot.

Carbon nanoring (CNR) with heptagon–pentagon defects is formed by single-walled carbon nanotubes (SWCNTs) (5, 5) and (9, 0) and each junction is constructed by connecting a heptagonal and a pentagonal carbon-atom ring. Then cutting the ring into two pieces along the junction, one pitch of carbon nanocoil will be obtained by constraining one end and stretching the other end along the helical axis. Molecular mechanics (MM) simulations are employed to investigate the mechanical characteristics of CNRs and nanocoils with and without defects. The Young's modulus of the nanoring with defects is about 282 GPa, which is larger than that of perfect nanorings with the similar ring radii, such as (5, 5) and (9, 0). The spring stiffness of the carbon nanocoil is calculated with a maximum value of 2.08 N/m, and it is found to be nonlinear and decreases with the increase in the relative elongation.

The interplay between the mechanical properties of double-stranded and single-stranded DNA is a phenomenon that contributes to various genetic processes in which both types of DNA structures coexist. Highly stiff DNA duplexes can stretch single-stranded DNA (ssDNA) segments between the duplexes in a topologically constrained domain. To evaluate such an effect, we designed short DNA nanorings in which a DNA duplex with 160 bp is connected by a 30 nt single-stranded DNA segment. The stretching effect of the duplex in such a DNA construct can lead to the elongation of ssDNA, and this effect can be measured directly using atomic force microscopy (AFM) imaging. In AFM images of the nanorings, the ssDNA regions were identified, and the end-to-end distance of ssDNA was measured. The data revealed a stretching of the ssDNA segment with a median end-to-end distance which was 16% higher compared with the control. These data are in line with theoretical estimates of the stretching of ssDNA by the rigid DNA duplex holding the ssDNA segment within the nanoring construct. Time-lapse AFM data revealed substantial dynamics of the DNA rings, allowing for the formation of transient crossed nanoring formations with end-to-end distances as much as 30% larger than those of the longer-lived morphologies. The generated nanorings are an attractive model system for investigation of the effects of mechanical stretching of ssDNA on its biochemical properties, including interaction with proteins.

Recently, we reported the synthesis of two novel large π-extended carbon nanorings by incorporating hexa-peri-hexabenzocoronenes: cyclo[12]-paraphenylene[2]-2,11-hexa-peri-hexabenzocoronene ([12,2]CPHBC) and the [4]cyclo-2,11-para-hexa-peri-hexabenzocoronene ([4]CHBC). The successful synthesis was achieved by the rationally designed pathways via palladium-, nickel-, or platinum-mediated reactions and the final aromatization reaction. This Synpacts article highlights the synthetic methods to achieve these carbon nanorings with large conjugated systems. We also summarize the representative characterization evidences and interesting photophysical properties of these carbon nanoring structures. Furthermore, the selective supramolecular host–guest interaction between [4]CHBC and C70 is briefly discussed. The new π-extended carbon nanorings can be considered as examples of longitudinal extension of the cycloparaphenylene scaffold, forming large conjugated CNT segments.1 Introduction2 Large π-Extended Carbon Nanorings by Incorporating Hexa-peri-hexabenzocoronenes3 Conclusions

In this paper, Fe nanoring model of different degree of eccentricity has been made. Based on the FFTM method and MC simulation method, the magnetic properties of the Fe nanoring, such as hysteresis loops, spin configuration, have been studied. The simulated results indicate that there are typical hysteresis loops and spin-configurations, such as onion-type state and vortex-type state in the system of symmetric Fe nanoring. The hysteresis loops of the eccentric Fe nanoring are similar to symmetric system when the degree of eccentricity is small, but as the degree of eccentricity increased, the magnetization behavior become different. Remanence is almost linearly related to the degree of eccentricity in the system of eccentric Fe nanoring, which can be explained by analyzing the change of spin-configurations in the eccentric Fe nanoring.

Magnetic hysteresis behavior of isotropic permalloy elliptic nanorings of outer semi-major axis length [Formula: see text] 100 nm and thickness [Formula: see text] 20 nm were studied with respect to the variation of two parameters: outer semiminor axis length [Formula: see text] and the difference between outer and inner dimensions [Formula: see text]. The outer semiminor axis length [Formula: see text] varied from 90 nm to 20 nm which covers from nearly circular nanoring to elliptic nanoring of high aspect ratio. The value of [Formula: see text] varied in steps of 10 nm. Micromagnetic simulation of in-plane hysteresis curve of these nanorings revealed that the remanent state of all of these elliptic rings are onion states if the magnetic field is applied along the longer side of the elliptic rings. If the magnetic field is applied along the shorter side, then the remanent states turn out to be vortex state. The hysteresis loss indicated by area of the hysteresis loop was found to be decreasing gradually with the increment of either [Formula: see text] or [Formula: see text]. On the other hand, the remanent magnetization increased with increment of [Formula: see text] but decreased with the increment of [Formula: see text]. The changes were attributed to three parameters mainly: inner curvature, exchange energy and demagnetization energy. The changes in loop area were discussed in light of variation of these three parameters.

In this work we investigate the characteristics and feasibility of a new class of magnetic particles that are optimized for possible biological applications as magnetic hyperthermia. These new nanostructures have the nanoring shape, being composed of iron oxides (magnetite or hematite). Such morphology gives the nanoparticles a peculiar magnetic behavior due to their magnetic vortex state. The iron oxide nanorings were obtained using hydrothermal synthesis. X-ray Diffraction confirmed the existence of the desired crystal structure and Scanning Electron Microscopy shows that the magnetite particles had nanometric dimensions with annular morphology (diameter ~250 nm). The nanorings also show intensified magnetic properties and a transition to a vortex state. This study showed that it is possible to obtain magnetic nanorings with properties that can be used in nanotechnological applications (mainly biotechnological ones aimed at the treatment and diagnosis of cancer), in large quantities in a simple synthesis route.

In this thesis, the growth of metal-free naphthalocyanine (Nc) and copper naphthalocyanine (CuNc) on both bare Si/SiO2 and octadecyltrichlorosilane (OTS) modified Si/SiO2 surface were studied. The effects of the substrate temperature on morphology and structure of Nc and CuNc thin film growth were presented. For these purposes thin films of Nc and CuNc prepared by thermal vacuum evaporation were studied using atomic force microscopy (AFM) and X-ray diffraction (XRD). We observed that the increase of substrate temperature during growth affects the morphology, preferential molecular orientation and degree of crystallinity of both Nc and CuNc thin film, which were used as active layers in organic field effect transistor (OFET) devices. Organic thin film transistors (OFETs) were fabricated using these molecules as the active layers and their electrical characteristics were measured under both vacuum and atmospheric conditions and they were found to exhibit p-type transistor action. A series of samples of the Nc and CuNc thin films were grown on Si/SiO2 and OTS-modified oxide surface at different substrate temperature but fixed equivalent deposited thickness. The growth conditions, particularly the substrate temperature strongly affect nucleation size and shape of the organic thin film. In general, the thin film morphology shows a near circular grain and elongated grain shape at low substrate temperature, while the thin Nc film shows small needle-like structure and extended needle-like crystalline structures with large gaps at high substrate temperature. The optimum substrate temperature during the growth of Nc on both surfaces is achieved at 200 °C, and this occurs for growth of CuNc at 180 °C and 160 °C on Si/SiO2 and OTS surfaces, respectively, for which the naphthalocyanine thin film shows the best morphological and electrical properties. We used Nc and CuNc thin films prepared at different substrate temperatures as active layers to fabricate bottom and top-contact organic field effect transistors. Their electrical characteristics were measured at room temperature in vacuum and air in the dark. We plotted the output characteristic and transfer characteristic of all OFET devices so that the effects of grain size and crystal structure on the performance characteristic of Nc OFET device could be investigated. Then we studied the effects of hysteresis and charge traps on device performance when exposed to air. We found that the changes generated by exposure of the device to atmosphere may be reversed by annealing the thin film to ∼100 °C in vacuum. We reported the highest mobility of (5.16 ± 0.23) × 10-2 cm2 /Vs for top-contact Nc device prepared at 200ºC on SiO2 after annealing in vacuum, and also we reported the highest mobility of (3.56 ± 0.14) × 10-2 cm2 /Vs for top-contact CuNc device prepared at 180ºC on SiO2 after annealing in vacuum. We found that the top-contact device always performs better than the bottom-contact device. We attributed this to the change of morphology of active layer in the interface between contact metal and SiO2. Solvent induced self-assembly, self-trapping, and self-organizing of c-P30 cyclic porphyrin polymers on the Au surface that are deposited from two solutions and various concentrations in ambient condition was also studied. This results in the arrangement of cyclic polymers in different configurations such as stacking columnar, supramolecular nesting and uniform height hexagonal close packed structure. These conformations are observed using scanning tunnelling microscopy. Highly covered surface stacking columnar like porous array is also observed. We show that toluene:methanol mixture can play a crucial role in self-assembly of supramolecular structure in two dimensions, π-π stacking conformation perpendicular over surface in three dimensions and single in double nested nanoring conformation. Cyclic porphyrin polymers deposited from toluene shows nested nanorings structure, such as single nanoring self-trapped inside a near-circular shape single ring on surface. Diluted solutions using a large volume of methanol relative to the toluene can suppress the adsorption of nanorings to the surface. Interestingly, adsorption of the cyclic polymer from toluene:methanol 3:5 can result in the formation of uniformly height hexagonal close packing on surface, where nanorings aggregate as columnar stacks in two layers, dependent on concentration. Our results show that the self-assembly of artificial cyclic polymers is dependent on solvent and concentration provides a significant step towards control of the three-dimensional arrangement of supramolecular conformation on surfaces using non-covalent interactions.

Frequently, the dental surgery one faces serious problems of defects osseous and loss of teeth; this means that those must be replaced by prostheses or implants to reconstitute the function and static. These materials were called biomaterials, since they interact with the systems made up of cells and fabrics. It is currently difficult to give a definition of "biomaterial" since the concepts changed in the last few years. We can however define a biomaterial as "a nonbiological material which interacts with biological systems" (Williams 1987). Since it interacts with biological systems, this material must be biologically accepted or at least no cause tissue injure; consequently we must also give a definition of "biocompatibility" which is "the capacity of a material to induce a suitable answer of the host for a specific application" (Williams 1987). These terms are appropriate in the majority of materials currently used like biomaterials, however the "nonbiological" term is not completely exact, since many materials used like biomaterials or medical devices are of biological origin, such is the case of bone grafts. One already used a large variety of materials like biomaterials, metals, ceramics, polymers, glasses, carbon, and composite materials. There are many examples of applications of the biomaterials: cardiac valves, articulations of knee, implants dental, intraocular lenses, etc. Now, many medical fields use the biomaterials. Each year in the United States more than 30. 000 prostheses of the knee and hip also 100. 000 to 300. 000 dental implants are placed (D. A. Puleo, 1999). In the European Community more than 50. 000 prostheses of hip and approximately 100. 000 dental implants are placed (SIMI Project). These statistics increase each year as the materials used get a greater safety with their patients, which also tend to lower the costs, by facilitating their good use gradually. One of most significant advanced in this field, was "the material bioactive" design. I. E. Works with the design and the development of biomaterials to which biologically activated molecules were built-in, in order to control the cellular answer. One conceived a series of process to this end by stressing polymer adhesion at surface of materials. The method suggested by Decher is of a great interest for self-assembly polyelectrolytes thin films made on the surface of materials. The alternate absorption of polyelectrolytes anion and cation on solid surfaces gives us the possibility of forming the multi-layer ones of very thin polyelectrolytes, which constitutes a versatile technique to modify surfaces. This possibility is of a great attraction for industry and medicine. The most significant characteristic of the polyelectrolytes is their capacities to be charged electrically in solution, which gives us the possibility of forming self-assembly polyelectrolytes films, with the possibility of intercalating and of immobilizing a large variety of made up on treated surface, such with inorganic particles or organics like proteins, the enzymes, etc, by providing to the surface of material really active characteristics, which constitute new strategies to control the answer of the host. This can be the key for the design and manufacture of biomaterials bioactives able to control the answer of the host at the molecular level by creating an adequate, fast and directed answer. Our work consisted in : the study of the formation of nanoring, the study of the adsorption of proteines on films in a field of precise pH, the study of the adhesion of cells on films of polyelectrolytes for micro aspiration. We studied the adsorption of the HSA on films made of polypeptides, the poly(L-lysine) (PLL), and the acid poly(glutamique) (PGA) in a field of pH 3. 0-10. 5. We showed that adsorption depends enormously on the last layer of the film. For the PLL, to low pH, an electrostatic repulsion limits adsorption. With the pH superiors one on adsorption of HSA on the PGA is observed. This is with the conformation of the rich PGA helical alpha which increases the roughness of film. Finally, we studied the adhesion of cells of films of polyelectrolytes. All the biological processes are achieved thanks to weak specific molecular interactions which generate connections of short duration; too strong interactions would remove all dynamics essential to the life. We thus evaluated by the technique of micromanipulation by micropipette the short-term interactions of cells with multi-layer films. By grafting hundreds of cells on a substrate, one will be able to distinguish the mechanical answers from the healthy cells. The goal of this work was the modulation of the multi-layer film properties with respect to the cellular adhesion. We observed also at the time of the deposit of PSS on a layer of PEI, the formation of circular structures. We named these structures of the nanorings. These structures are variable sizes of 300 Nm diameters to 2 µm diameter between the various experiments but by experiment, are of very homogeneous size. Such structures had never been observed. We thus sought to include/understand the mechanisms of controls and formation of these structures. These observations were realizes in AFM by using a liquid cell which prevents the appearance of artefacts due to dehydration. We determined that the two parameters which control the size of the nanoring are the size of the pores of the filters used for the preparation of the solution of PSS and the time of contact of the solutions with the air. Indeed, divalent ions CO3 -- play a dominating role in the formation of this nanoring. It is about a mechanism of car-assembly of hydrophobic complexes of PSS on the surface of film of PEI. The size being controlled by a balance enters the electrostatic repulsions and hydrophobic attractions and under the dependence of the electrostatic interactions between the PEI and the PSS
Fréquemment, la chirurgie dentaire fait face à de graves problèmes de défauts osseux et compris la perte de dents; ceci signifie que celles-ci doivent être remplacées par des prothèses ou implants pour reconstituer la fonction et l'esthétique. Ces matériaux ont été appelés des biomatériaux, puisqu'ils interagissent avec les systèmes constitués de cellules et de tissus. Il est actuellement difficile de donner une définition de " biomatériau " puisque les concepts ont changé durant ces dernières années. Nous pouvons toutefois définir un biomatériau comme " un matériau non biologique qui interagit avec des systèmes biologiques " (Williams 1987). Puisqu'il interagit avec des systèmes biologiques, ce matériau doit biologiquement être accepté ou au moins ne pas provoquer de dommages tissulaires ; par conséquent nous devons aussi définir le terme " biocompatibilité " qui est " la capacité d'un matériau à induire une réponse appropriée de l'hôte pour une application spécifique " (Williams 1987). Ces termes conviennent à la majorité des matériaux actuellement utilisés comme biomatériaux, toutefois le terme " non biologique " n'est pas tout à fait exact, puisque beaucoup des matériaux utilisés comme biomatériaux ou dispositifs médicaux sont d'origine biologique, tel est le cas des greffes de tissus. On a déjà utilisé une grande variété de matériaux comme biomatériaux, métaux, céramique, polymères, verres, carbone, et matériaux composites. Il existe de nombreux exemples d'applications des biomatériaux : les valves cardiaques, les articulations de genou, les implants dentaires, les lentilles intraoculaires, etc. Actuellement, de très nombreux domaines médicaux utilisent les biomatériaux. Chaque année aux Etats-Unis plus de 30. 000 prothèses du genou et de hanche aussi que 100. 000 à 300. 000 implants dentaires sont placés (D. A. Puleo, 1999). Dans la Communauté Européenne sont placés plus de 50. 000 prothèses de hanche et environ 100. 000 implants dentaires (SIMI Project). Ces chiffres augmentent chaque année au fur et à mesure que les matériaux utilisés procurent une plus grande sécurité à leurs patients, ce qui tend aussi à abaisser les coûts, en facilitant progressivement leur bon usage. Une des avancées les plus importantes dans ce domaine, a été la conception de " matériaux bioactifs ". C'est-à-dire que l'on travaille à la conception et l'élaboration de biomatériaux auxquels des molécules biologiquement activées ont été incorporées, afin de contrôler la réponse cellulaire. On a conçu une série de processus dans ce but en mettant l'accent sur l'adhésion de polymères à la surface des matériaux. La méthode proposée par Decher est d'un grand intérêt pour l'autoassemblage de film de polyélectrolytes à la surface des matériaux. L'absorption alternée de polyélectrolytes anioniques et cationiques sur des surfaces solides nous donne la possibilité de former des multicouches de polyélectrolytes très minces, ce qui constitue une technique ubiquitaire pour modifier des surfaces. Cette possibilité est d'un grand attrait pour l'industrie et la médecine. La caractéristique la plus importante des polyélectrolytes est leur capacités d'être chargé électriquement en solution, ce qui nous donne la possibilité de former des films alternés de polyélectrolytes autoassemblés, avec la possibilité d'intercaler et d'immobiliser une grande variété de composés sur la surface traitée, telles de particules inorganiques ou organique comme des proteines, les enzymes, etc. , en fournissant à la surface du matériau des caractéristiques réellement actives, qui constituent de nouvelles stratégies pour contrôler la réponse de l'hôte. Celle-ci peut être la clé pour la conception et fabrication de biomatériaux bioactifs capables de contrôler la réponse de l'hôte au niveau moléculaire en créant une réponse adéquate, rapide et dirigée. Notre travail a consisté en : l'étude de la formation de nanoring, l'étude de l'adsorption de proteines sur des films dans un domaine de pH précis, l'étude de l'adhésion de cellules sur des films de polyelectrolytes pour micro aspiration. Nous avons observé lors du dépôt de PSS sur une couche de PEI, la formation de structures circulaires. Nous avons nommé ces structures des nanorings. Ces structures sont de tailles variables de 300 nm de diamètre à 2 µm de diamètre entre les différentes expériences mais par expérience, sont de taille très homogène. De telles structures n'avaient jamais été observées. Nous avons donc cherché à comprendre les mécanismes de contrôles et de formation de ces structures. Ces observations ont été réalise en AFM en utilisant une cellule liquide qui prévient l'apparition d'artéfacts dus à la déshydratation. Nous avons déterminé que les deux paramètres qui contrôlent la taille des nanoring sont la taille des pores des filtres utilisés pour la préparation de la solution de PSS et le temps de contact des solutions avec l'air. En effet, les ions divalents CO3—jouent un role prépondérant dans la formation de ces nanoring. Il s'agit d'un mécanisme d'auto-assemblage de complexes hydrophobiques de PSS à la surface du film de PEI. La taille étant contrôlée par une balance entre les répulsions électrostatiques et les attractions hydrophobiques et sous la dépendance des interactions électrostatiques entre le PEI et le PSS. Nous avons étudié aussi l'adsorption de la HSA sur des films formé de polypeptides, la poly(L-lysine) (PLL), et l'acide poly(glutamique) (PGA) dans un domaine de pH 3. 0-10. 5. Nous avons démontré que l'adsorption dépend énormément de la couche supérieure des films. Pour le PLL, à pH bas, une répulsion électrostatique limite l'adsorption. Aux pH supérieurs une sur adsorption de HSA sur le PGA est observé. Ceci est du à la conformation du PGA riche en hélice alpha qui augmentent la rugosité du film. Finalement, nous avons étudié l'adhésion de cellules des films de polyelectrolytes. Tous les processus biologiques s'accomplissent grâce à des interactions moléculaires spécifiques faibles qui génèrent des liaisons de courte durée; des interactions trop fortes supprimeraient toute la dynamique indispensable à la vie. Nous avons donc évalué par la technique de micromanipulation par micropipette les interactions à court terme de cellules avec des films multicouches. En greffant des centaines de cellules sur un substrat, on pourra distinguer les réponses mécaniques des cellules saines. Le but de cette travail a été la modulation des propriétés de films multicouches vis à vis de l'adhésion cellulaire

In the pursuit of economical and rapid fabrication solutions on the micro and nano scale, polymer replication has proven itself to be a formidable technique, which despite zealous development by the research community, remains full of promise. This thesis explores the potential of elastomers in what is a distinctly multidisciplinary field. The focus is on developing innovative fabrication solutions for planar photonic devices and for nanoscale devices in general. Innovations are derived from treatments of master structures, imprintable substrates and device applications. Major contributions made by this work include fully replicated planar integrated optical devices, nanoscale applications for photolithographic standing wave corrugations (SWC), and a biologically templated, optical fiber based, surface-enhanced Raman scattering (SERS) sensor. The planar devices take the form of dielectric rib waveguides which for the first time, have been integrated with long-period gratings by replication. The heretofore unemployed SWC is used to demonstrate two innovations. The first is a novel demonstration of elastomeric sidewall photolithographic mask, which exploits the capacity of elastomers to cast undercut structures. The second demonstrates that the corrugations themselves in the absence of elastomers, can be employed as shadow masks in a directional flux to produce vertical stacks of straight lines and circles of nanowires and nanoribbons. The thesis then closes by conceptually combining the preceding demonstrations of waveguides and nanostructures. An optical fiber endface is em ployed for the first time as a substrate for patterning by replication, wherein the pattern is a nanostructure derived from a biological template. This replicated nanostructure is used to impart a SERS capability to the optical fiber, demonstrating an ultra-sensitive, integrated photonic device realized at great economy of both time and money, with very real potential for mass fabrication.

Les oligophénylènes constituent une classe de molécules centrale dans la conception de semi-conducteurs organiques pour des applications optoélectroniques. Ces travaux portent sur la synthèse et l’étude approfondie de dérivés linéaires et cycliques du fluorène (un biphényle rigidifié par un pont méthylène), fragment constitutif essentiel dans l’électronique organique. Nous nous intéressons en particulier aux relations structure-propriétés de ces systèmes π-conjugués. Dans une première partie, avec comme cadre le développement de matériaux hôtes pour diodes électroluminescentes (PhOLEDs), nous présentons une étude de la régioisomérie de phényl-fluorènes et de phényl-spirobifluorènes. Ses résultats ont permis la préparation de quatre matériaux hôtes purs hydrocarbures, dimères de spirobifluorène, intégrés dans des PhOLEDs bleues à hautes performances. Dans une seconde partie, nous nous intéressons au domaine récent des nano-anneaux moléculaires, objets cycliques présentant une conjugaison π de nature singulière. Après une revue bibliographique portant sur les cycloparaphénylènes et leurs propriétés, nous présentons nos études concernant plusieurs exemples de leurs analogues pontés : les cycloparafluorènes
Oligophenylenes constitute a major class of molecules in the design of organic semiconductors for optoelectronics applications. This work involves the synthesis and in-depth study of linear and cyclic derivatives of fluorene (a biphenyl rigidified by a methylene bridge), an essential building block in organic electronics. We focus our attention on the structure-property relationships of these π-conjugated systems. In a first part, within the framework of host materials for phosphorescent organic light-emitting diodes (PhOLEDs), we present a regioisomerism study of phenyl-fluorenes and phenyl-spirobifluorenes. Its results enabled the preparation of four pure hydrocarbon host materials, spirobifluorene dimers, used in high-performance blue PhOLEDs. In a second part, we take interest in the emerging field of molecular nanorings, cyclic objects presenting a singular nature of π-conjugation. After a bibliographical review covering cycloparaphenylenes and their properties, we present our studies regarding several examples of their bridged analogues: cycloparafluorenes

This thesis presents a combined experimental and computational evaluation of the physical-organic properties of butadiyne-linked porphyrin oligomers. The principal result from the thesis is the synthesis and characterisation of the largest aromatic and antiaromatic systems to date, in the form of an oxidised [6]-porphyrin nanoring, with diameter 2.4 nm. This large electronically coherent system provides insight into the connection between aromatic ring currents and persistent currents in metal and semiconductor mesoscopic rings. Chapter 1 briefly reviews the concepts used in the remainder of the thesis, with a particular focus on aromaticity. In Chapter 2, the barrier to inter-porphyrin torsional rotation in a butadiyne-linked porphyrin dimer is determined computationally and experimentally to be 3 kJ mol^-1. The barrier height is closely related to the resonance delocalisation energy between the porphyrin subunits. In Chapter 3 we show that by oxidising a butadiyne-linked [6]-porphyrin nanoring to its 4+ and 6+ oxidation states, the nanoring becomes antiaromatic and aromatic respectively. In contrast, the neutral oxidation state exhibits only local aromaticity for the six porphyrin units. The 12+ cation can also be generated, and exhibits local antiaromaticity for each porphyrin unit. The characterisation of (anti)aromaticity employs NMR and computational techniques. In Chapter 4, the properties of cation radicals of linear and cyclic porphyrin oligomers are explored. Cations generated by spectroelectrochemistry are measured by optical spectroscopies, and chemically generated radical monocations are examined by cw/pulsed EPR spectroscopies. EPR and optical spectroscopies agree that the dimer monocation radical is fully delocalised, in Robin-Day Class III, whereas the monocations of longer oligomers are localised over 2-3 porphyrin units (Class II). In Chapter 5, photophysical and computational investigations into excited state aromaticity in porphyrin nanorings are presented. The computational results suggest the presence of aromaticity in the triplet excited states, but experiment fails to convincingly demonstrate the effect. Computational results in Chapter 6 show that a butadiyne linked [6]-porphyrin nanoring in which one butadiyne (C≡C-C≡C) is truncated to an alkyne (C≡C) exhibits a reversal of aromaticity and antiaromaticity in its oxidised states, compared to the all-butadiyne linked nanoring, consistent with Hückel's law.

This report gives a short introduction of the Norwegian wireless electronics company Chipcon AS, and goes on to account for the state of the art of small IP processor cores. It then describes the NanoRisc, a powerful processor developed in this project to replace hardware logic modules in future Chipcon designs. The architecture and a VHDL implementation of the NanoRisc is described and discussed, as well as an assembler and instruction set simulator developed for the NanoRisc. The results of this development work are promising; synthesis shows that the NanoRisc is capable of powerful 16-bit data moving and processing at 50 MHz in an 18nm process while requiring less than 4500 gates. The report concludes that the NanoRisc, and none of the existing IP cores studied, satisfies the requirements for hardware logic replacement in Chipcon transceivers.

New templates based on the structures of cyclodextrin and ferrocene have been developed for porphyrin nanoring syntheses. Flexibility can be taken into account of the molecular template design. The flexibility of butadiyne bonds allow the formation of a 5-porphyrin nanoring, which is the smallest fully-conjugated porphyrin nanoring to date. Chapter 1 describes the general information of porphyrin, cyclodextrin and ferrocene, which are used as basic structures in the thesis. The polymer chemistry of porphyrins is reviewed as the background knowledge of the work. Meanwhile, chelate cooperativity of supramolecular systems and the corresponding measurement method are introduced. Chapter 2 presents the chemistry towards 6- and 7-porphyrin nanorings using molecular templates T6* and T7*, which are based on the a- and β-cyclodextrin scaffolds. The cooperativity of respective template-nanoring complexes was investigated by UV-vis titrations. Chapter 3 describes the Vernier-templated syntheses of porphyrin nanorings using T7* and different linear porphyrin oligomers (l-P2, l-P4 and l-P8). Both chapters focus on the influences of spatial preorganization and flexibility to the cooperativity of supramolecular systems. Chapter 4 introduces the chemistry towards a ferrocene-based five-dentate template T5 which successfully directed the syntheses of 5-porphyrin nanorings. Investigation of the cooperativity in the nanoring-template system is presented. Chapter 5 investigates the cooperativity between T5 and linear porphyrin oligomers in detail; and focuses on the contribution of partially-bound complexes in the measurement of equilibrium constants of the host-guest systems. Both chapters focus on the influences of intramolecular strain to the cooperativity in supramolecular systems. Chapter 6 provides experimental procedures and characterization data of the known and novel compounds synthesized in the course of completing the thesis.

This thesis is concerned with the photophysical properties of porphyrin nanorings. In particular, the impact of symmetry, conformation and structure on electronic delocalization, radiative rate and emission polarization memory loss are investigated and exciton migration is probed on a number of porphyrin nanorings. Ultrafast time-resolved spectroscopy techniques are used to study the fluorescence dynamics of these newly synthesized compounds. First, photophysical implications of lifting the rotational symmetry are investigated using a number of small porphyrin rings specially modified for this purpose. For more severe symmetry distortions, increased optical transitions to the lowest excited state have been observed, which is dipole-forbidden due to symmetry reason. Also, the degeneracy in the allowed first excited state is lifted for broken symmetry, leading to a polarization switching effect. The effect of conformation on emission depolarization memory loss is studied using a series of similarly sized porphyrin rings with rigid structures exhibiting various degrees of out-of-plane distortion. Excitations can access any segment on the nanoring and this is not affected by the conformation. However, severe out-of-plane distortions lead to lowered emission anisotropy; this conclusion is further supported by molecular dynamics simulation. Finally, exciton migration within porphyrin ring complex is investigated. Russian doll complex which consists of two concentric porphyrin rings acts as a single emitter, even though spectral features of both ring components are found in the absorption spectrum. Lifetimes and radiative rates of the complex and the individual rings components further confirmed that excitons migrate from the outer 12-ring to the inner 6-ring within 40 ps. A nanotube consisting of two conjugated 6 porphyrin rings linked by dimers acting as staves also exhibits energy migration. Emission anisotropy measurements suggest that excitation is transferred from the staves of the nanotube to the ring plane effectively within 280 fs.

This thesis describes supramolecular approaches to porphyrin nanorings. Cyclic porphyrin arrays resemble natural light harvesting systems, and it is of interest to probe the photophysical effects of bending the porphyrin aromatic π-system. A general overview of the synthesis and photophysical properties of porphyrins and their arrays is carried out in Chapter 1. The electronic structure of porphyrins is examined, and how conformational effects in oligomers, such as inter-porphyrin torsional angle and backbone bending influence the π-conjugation pathway. The structures of light harvesting complexes are discussed. Chapter 2 describes the design and synthesis of a complementary 12-armed template designed to coordinate linear porphyrin oligomers in the correct conformation for cyclisation to give a cyclic porphyrin dodecamer. Chapter 3 demonstrates two approaches to a cyclic porphyrin dodecamer ring. Firstly, a classical templating approach using the 12-armed template is described. The limitations of this approach in the quest for larger nanorings are discussed. Vernier templating, which utilises a mismatch in the number of binding sites between a ligand and its receptor is introduced as a general strategy to the synthesis of large nanorings. This is demonstrated by the synthesis of cyclic dodecamer from a linear porphyrin tetramer and a hexadentate template via a figure-of-eight intermediate. The general utility of the Vernier method to large nanorings is explored in Chapter 4 with steps towards the synthesis of a cyclic tetracosamer, consisting of 24 porphyrin subunits. In preliminary experiments, an improved route to the cyclic porphyrin octamer is described. Finally, the photophysical properties of the nanoring series are explored in Chapter 5 as a function of size and conformation. Femtosecond photoluminescence spectroscopy shows that even in cyclic dodecamer, exciton delocalisation over the entire porphyrin backbone occurs on a sub-picosecond timescale, and parallels are drawn with the dynamics of natural light harvesting complexes.

This study focuses on the nanopiezoelectric energy harvesting mechanism of free-floating zinc oxide (ZnO) nanorings. Inner and outer surfaces of a ZnO nanoring are both deposited with an electrode layer that are uniformly and symmetrically segmented into series of couples to serve as distributed energy generators. The generation mechanism of voltage signal is analyzed first, followed by the energy generation analysis. Because of the cancellation of the electric potentials across the nanoring thickness induced by bending strains, the membrane strain is the only contribution to the output voltage and energy generations. The membrane (circumferential) oscillation modes of the nanoring are considered for the analysis of energy generation mechanism. Distributions of the output voltage signal and the generated energy are evaluated with respect to various nanoring modes and design parameters, e.g., nanoring radii and electrode segment sizes. Signal average and cancellation effect reduces the generated signal and energy when the segment size enlarges. The overall energy is also calculated by summing up energies generated from all energy harvesters of the whole nanoring. Analysis suggests that more energy can be generated when the segment size reduces. The energy distributions with respect to nanoring modes provide a design guideline to select proper segmentation and nanoring radius, as well as optimal distributions of electrode patches to achieve highest energy harvesting efficiency for nanoring generators.