The method of the deposition of films of small molecules for use in electronic applications is just as important as the molecule design itself as the film’s morphology and continuity influence the performance of the devices that they are incorporated in. The purpose of the work in this thesis was to develop a method of electrochemically depositing films of small molecules for potential use in electronic applications. A method of electrochemically depositing films of chemically reduced low solubility dye molecules was successfully pioneered. The process was developed using N,N dibutyl-3,4,9,10-perylene-bis(dicarboxime), a simplified version of 3,4,9,10-perylene-tetracarboxylic bisbenzimidalzole. Both of these dyes have been used in electronic applications, but low solubility makes them difficult to deposit by traditional solution techniques. A series of films was electrochemically deposited onto FTO coated glass and field effect transistors using coulometry. These films were characterised by absorption spectroscopy, photoluminescence, scanning electron microscopy, X-ray diffraction and photo-electrochemistry. The same deposition method was applied to copper phthalocyanine. These films were characterised by absorption spectroscopy, photoluminescence, scanning electron microscopy and X-ray diffraction. The developed method was used to deposit films of bilayers of dyes and to investigate the dye penetration during the deposition of copper phthalocyanine onto porous titanium dioxide. Films of neutral copper and nickel dithiolenes were electrodeposited from air-stable TMA salts to investigate the absorbance of the near infrared species formed, as well as to investigate the conductivity of both complexes and the magnetoresponse of the neutral copper dithiolene which is air unstable when formed chemically.

Post-functionalization of 3,5-bis(2-pyridyl)-4-hydro-1,2,4,6-thiatriazine (Py2TTAH) and its synthetic precursors have been explored through alkylation, arylation, and coordination. While alkylation was initially pursued at the central nitrogen atom of Py2TTAH, functionalization instead occurred on the sulfur atom. Consequently, the proclivity of the sulfur towards alkylation and arylation was studied. Neutral 3,5-bis(2-pyridyl)-S-methyl-1,2,4,6-thiatriazine (S-Me-Py2TTA) and 3,5-bis(2-pyridyl)-S-ethyl-1,2,4,6-thiatriazine were achieved via either anionic or cationic intermediates, and all isolable species were fully characterized. In addition, an aromatic derivative, 3,5-bis(2-pyridyl)-S-phenyl-1,2,4,6-thiatriazine was obtained through reactions using hypervalent iodide as an electrophile. Functionalization of Py2TTAH and S-Me-Py2TTA was also explored through coordination with iron. The synthesis and crystal structures of two different iron complexes are described. The incorporation of boron with Py2TTAH and its precursor, N-2-pyridylimidoyl-2-pyridylamidine was also considered. Both compounds afforded the same boratriazine ring. Overall, this thesis describes the groundwork for future functionalization of the Py2TTA framework, and its potential for molecular materials applications.

No description available.

The field of molecular electronics has been under investigation by materials scientists for the last two decades, activity that has increased in recent years as their potential to be components in modern quantum computing devices began to be discussed in a more sophisticated manner. In this field, the challenge is to obtain stable highly conducting materials and to manipulate their properties with external stimuli. As one of the most stable organic radicals, the singly reduced form of TCNQ (7,7,8,8-tetracyanoquinodimethane) has played a central role in the design of many unprecedented conducting materials including the first purely organic conductor (TTF)(TCNQ) (TTF = tetrathiafulvalene) which is nearly metallic and the electrically bistable switching material Cu(TCNQ). The research in this dissertation focused on the application of TCNQ and its derivatives in order to tune the structure and conductivity of these materials, with the overarching goal being to understand the mechanism of conductivity. This dissertation reports the details of the first main-group TCNQ binary compound, Tl(TCNQ). Two distinct polymorphs have been discovered and a remarkable water-induced phase transition from one to the other was observed. With different modes of TCNQ stacking (alternating or homogenous distances), the two polymorphs exhibit very different conductivities, namely 2.4×10^-4 S/cm and 5.4×10^-1 S/cm. With this inspiration, a series of semiconductors, Tl(TCNQX2) (X =Cl, Br, I) was prepared and structurally characterized. The steric effect of the halogen substituents leads to a variety of structures and a band structure simulation has suggested a clear structure-property relationship that involves perturbation of the Tl 6s orbital into the conduction band. Inspired by the switching material Ag(TCNQ), semiconducting frameworks Ag(TCNQCl2) and Ag(TCNQBr2) were prepared by electrocrystallization methods. Importantly, the former material exhibits a high room temperature conductivity of 0.25 S/cm and an unusual room temperature negative differential resistance (NDR) which is the source of intrinsic switching behaviors. The effect of solvent on the structure of these binary phases was also investigated. The series M(TCNQX2)(MeCN)n (M = Cu, Ag; X = Br, I; n =1, 2) was discovered and the interconversion of these solvated phases was studied. The effect of coordinated solvent molecules decreases the density of conducting stacks, consequently leading to a decrease of conductivity.

La méthodologie classique pour la synthèse de matériaux à transition de spin a un certain degré d’irréproductibilité du fait de l’imprévisibilité des flux turbulents à l’intérieur du milieu réactionnel contenu dans la verrerie ordinaire de laboratoire. Pour tenter de résoudre ce problème, nous explorons la microfluidique de gouttelettes sans tensioactifs comme une nouvelle méthode d’obtention de matériaux à transition de spin.Après avoir testé divers dispositifs microfluidiques, nous avons synthétisé le MOF de type Hofmann [Fe(pz)Pt(CN)4] en combinant deux solutions de réactifs dans un canal débouchant immédiatement dans une buse de focalisation de flux. Le produit obtenu présente une réduction drastique de la taille de particule par rapport aux méthodes classiques, et affiche un comportement magnétique consistent avec les nanoparticules rapportées antérieurement.Malheureusement, du fait des hautes concentrations utilisées ici, la réaction se produit très rapidement, et le dispositif peut facilement se boucher si les flux sont modifiés ou perturbés. Pour résoudre ce problème, nous avons développé une nouvelle méthode : une substance causant un gonflement du PDMS est mélangée avec l’huile de la phase continue pour obtenir une réduction des dimensions du dispositive, et ainsi réduire le diamètre des gouttes de presque deux ordres de grandeur. / The conventional methodology to synthesize spin-crossover materials has some degree of irreproducibility due to the unpredictability of the turbulent flows in the reaction media contained in ordinary laboratory glassware. To address this issue, we explore surfactant-free droplet microfluidics as a new method to synthesize spin-crossover materials.After probing the use of different microfluidic devices, we synthesized the Hofmann type MOF [Fe(pz)Pt(CN)4] by combining two solutions with reactants into a channel that immediately reaches a flow-focusing junction. The product obtained displays a strong decrease in its particle size compared with the batch synthesis. The obtained nanoparticles display a magnetic behavior consistent with the nanoparticles reported previously.Unfortunately, under the high concentrations used here, the reaction occurs very quickly, and the device can easily clog when the flow rates are changed. This leads to difficulties when attempting to modulate the dimensions of the droplets without affecting the general performance of the device. To solve this problem, we developed a new method where a swelling agent is combined with the oil used as the continuous phase, resulting in a change in the critical dimensions of the PDMS chip and a change of the diameter of the droplets of almost two orders of magnitude.

We have used ab initio computational simulation techniques to investigate both intra- and intermolecular interactions in a novel family of ionic organophosphonate molecular crystals. We have examined the influence of various numerical approximations on the computed geometry and binding energies of a selection of well-characterised hydrogen bonded systems. It was found that numerical basis sets provided the efficiency required to study the large hydrogen bonded dimer anions present in the organophosphonate system, while also producing accurate geometries and binding energies. We then calculated the relaxed structures and binding energies of phenylphosphonic acid dimer in the two arrangements in which it is present in the bulk crystal. The computed geometries were in excellent agreement with the experimental structures and the binding energies were consistent with those found for other ionic hydrogen bonded systems. Electron density maps were used to gain insight into the nature of the hydrogen bonding interaction between phenylphosphonic acid dimers. We also examined the effect of aromatic ring substituents on the geometry and energetics of the hydrogen bonding interaction. The nitro-substituted dimer was predicted to have a stronger binding energy than its unsubstituted parent while the methyl-substituted dimer was predicted to have a similar binding energy to its unsubstituted parent. An analysis of crystal field effects showed that the structure of the phenylphosphonic acid dimers in the organophosphonates is a complex product of competing intra- and intermolecular forces and crystal field effects. Cooperative effects in the organophosphonate system were also investigated and it was found that the interactions were mostly one-body (local) in nature. We have examined the intramolecular charge-transfer interaction between copper-halogen cations in the organophosphonate materials. The origin of geometric differences between the Cu(I) starting material and Cu(II) product cations was attributed to the electronic configuration of the Cu ion, not crystal field effects. To gain further insight into the difference in electronic structure between the starting material and product, we attempted to simulate the step-by-step dissociation of the [CuI]+ system. Although this investigation was not successful, we were able to expose some of the pitfalls of simulating dissociating odd-electron systems. We also analysed and compared the charge-transfer interaction in the chloro-, bromo- and iodo-forms of the organophosphonate family. The charge-transfer interaction was predicted to increase on going from the chloro- to the iodo-form, consistent with solid-state UV-visible data. Finally, we used the highly accurate Quantum Monte Carlo (QMC) method to investigate the hydrogen bonding interaction in water dimer and to calculate the dissociation energy. The accuracy of the experimental estimate for the dissociation energy has recently been questioned and an alternative value has been put forward. Our results lend support to the validity of the alternative value and are also in excellent agreement with those from other high-level calculations. Our results also indicate that QMC techniques are a promising alternative to traditional wavefunction techniques in situations where both high accuracy and efficiency are important.

This thesis focuses on theoretical study of charge transportproperties in molecular systems. The understanding of the transportprocess and mechanism in molecular systems is essential forthe design of new functional molecular materials and molecularelectronic devices. The molecular junctions and organic molecularcrystals have been used as the model systems to highlight the usefulnessof theoretical modelling. A molecular junction is a system that consists ofone or several molecules sandwiched between two electrodes.The charge transport in molecular junctions is a very complex processthat is affected by the interaction between molecules and electrodes,the surroundings, as well as electron-electron (e-e) andelectron-phonon (e-p) couplings. When the molecule-electrode couplingis strong, the transport process can be very quick. If the e-p couplingis weak, the inelastic tunneling has only negligible contributions to thetotal current and the elastic electron tunneling plays the dominant role.Furthermore, the hopping process becomes dominant in the case of strong e-pcoupling, for which the geometric relaxation of the molecule needsto be considered. In this thesis, we have examined these three kinds oftransport processes separately. The first studied system is a molecular junction consisting of aromaticallycoupled bimolecules. Its elastic electron tunneling property is simulatedusing Green's functional theory at density functional theory level.The dependence of the conductance of bimolecular junctions on the vertical distances,horizontal distances and the tilt angles has been systematically studied. Theinelastic electron tunneling spectra (IETS) of molecular junctions have beencalculated for several systems that were experimentally measured with conflictingresults and controversial assignments. Our calculations provide the reliableassignments for the experimental spectra and revealed unprecedented detailsabout the molecular conformations within the junctions under different conditions.It demonstrates that a combined theoretical and experimental IETS study is capableof accurately determining the structure of a single molecule inside the junction.The hopping process is a dominant charge transfer process in organic molecularcrystals. We have studied the charge transport ability of four kinds of n-typeorganic semiconductor materials to find out the related structure-to-propertyrelationship. It is done by adopting the quantum charge transfer rate equationcombined with the random walk approach. / QC 20120515

The aim of this thesis was to investigate carbon based molecular materials at first principles levels. Special attention has been paid to simulations of X-ray spectroscopies, including near edge X-ray absorption fine structure (NEXAFS), X-ray photoelectron, and X-ray emission spectroscopy, which can provide detailed information about core, occupied and unoccupied molecular orbitals of the systems under investigation. Theoretical calculations have helped to assign fine spectral structures in high resolution NEXAFS spectra of five azabenzenes (pyridine, pyrazine, pyrimidine, pyridazine and s-triazine), and to identify different local chemical environments among them. With the help of NEXAFS, the characters of important chemical bonds that might be responsible for the unique magnetic properties of the tetracyanoethylene compound has been revealed. Calculations have demonstrated that X-ray spectroscopies are powerful tools for isomer identification and structure determination of fullerenes and endohedral metallofullerenes. A joint experimental and theoretical study on metallofullerene Gd@C82 has firmly determined its equilibrium structure, in which the gadolinium atom lies above the hexagon on the C2 axis. It is found that the gadolinium atom could oscillate around its equilibrium position and that its oscillation amplitude increases with increasing temperature. In this thesis, several new computational schemes for large-scale systems have been proposed. Parallel implementation of a central insertion scheme (CIS) has been realized, which allows to effectively calculate electronic structures of very large systems, up to 150,000 electrons, at hybrid density functional theory levels. In comparison with traditional computational methods, CIS provides results with the same high accuracy but requires only a fraction of computational time. One of its applications is to calculate electronic structures of nanodiamond clusters varying from 0.76 nm (29 carbons) to 7.3 nm (20,959 carbons) in diameter, which enabled to resolve the long-standing debate about the validity of the quantum confinement model for nanodiamonds. Electronic structures and X-ray spectroscopies of a series of single-walled carbon nanotubes (SWCNTs) with different diameters and lengths have been calculated, which have made it possible to interpret the existing experimental results. / QC 20100727

Neutral radicals represent versatile building blocks for the design of new conductive and magnetic molecular materials. In order to obtain good electron transport, materials displaying a high bandwidth W and a low on-site Coulomb repulsion energy U must be generated, and to this end, the pyridine-bridged bisdithiazolyl radicals were developed. As a result of resonance stabilization, these materials possessed a low U, a high thermal stability, and did not dimerize in the solid state. Unfortunately, their crystal structures consisted of slipped π-stack arrays that limited overall bandwidth and afforded Mott insulating ground states. To improve on these systems, two strategies were employed to increase orbital overlap between radicals. The first approach involved the removal of one of the R groups to allow for more superimposed π-stacking in the solid state. Although the desired packing motif was achieved for one derivative, and higher conductivity was observed, a subtle distortion along the π-stacks at low temperature resulted in diamagnetic behaviour, demonstrating the need for steric protection in preventing spin-quenching association in these compounds. The second strategy to improve W was to incorporate the heavier, more spatially diffuse selenium atom into the framework. Three selenium-containing isomers were developed and it was found that conductivity increased with selenium content, with room temperature values reaching 0.001 S/cm. For some derivatives σ-dimerization through the selenium atom is observed, and these compounds exhibited a dramatic response to applied pressure, with conductivity values increasing by 5 orders of magnitude under 5 GPa of pressure. When dimerization is avoided, isomorphous mapping of sulfur for selenium is generally achieved, although for one series of radicals, two space groups were obtained. For this family of compounds the effects of the crystal structure on the transport properties were examined. A series of EHT bandwidth calculations and DFT magnetic exchange energy calculations on a model 1D π-stack of radicals revealed that the experimental properties (both conductivity and magnetism) correlate well to theory, suggesting that the behaviour of these compounds can be predicted based on crystal structure, and that the design of compounds with specific properties may soon be possible.

Neutral radicals represent versatile building blocks for the design of new conductive and magnetic molecular materials. In order to obtain good electron transport, materials displaying a high bandwidth W and a low on-site Coulomb repulsion energy U must be generated, and to this end, the pyridine-bridged bisdithiazolyl radicals were developed. As a result of resonance stabilization, these materials possessed a low U, a high thermal stability, and did not dimerize in the solid state. Unfortunately, their crystal structures consisted of slipped π-stack arrays that limited overall bandwidth and afforded Mott insulating ground states. To improve on these systems, two strategies were employed to increase orbital overlap between radicals. The first approach involved the removal of one of the R groups to allow for more superimposed π-stacking in the solid state. Although the desired packing motif was achieved for one derivative, and higher conductivity was observed, a subtle distortion along the π-stacks at low temperature resulted in diamagnetic behaviour, demonstrating the need for steric protection in preventing spin-quenching association in these compounds. The second strategy to improve W was to incorporate the heavier, more spatially diffuse selenium atom into the framework. Three selenium-containing isomers were developed and it was found that conductivity increased with selenium content, with room temperature values reaching 0.001 S/cm. For some derivatives σ-dimerization through the selenium atom is observed, and these compounds exhibited a dramatic response to applied pressure, with conductivity values increasing by 5 orders of magnitude under 5 GPa of pressure. When dimerization is avoided, isomorphous mapping of sulfur for selenium is generally achieved, although for one series of radicals, two space groups were obtained. For this family of compounds the effects of the crystal structure on the transport properties were examined. A series of EHT bandwidth calculations and DFT magnetic exchange energy calculations on a model 1D π-stack of radicals revealed that the experimental properties (both conductivity and magnetism) correlate well to theory, suggesting that the behaviour of these compounds can be predicted based on crystal structure, and that the design of compounds with specific properties may soon be possible.