Structure, dynamics and thermal reactivity of pigments and other organic solid

DPP pigments belong to a commercial family of pigments. They have all the attributes that a successful pigment requires, including high insolubility in common solvents which leads to difficulties in their application. This problem has been overcome by the incorporation of solubilising Boc groups. These can be removed by heating, thereby recovering the desired pigment. The kinetics of the solid state thermal decomposition reaction of DPP-Boc have been probed in detail using a range of complementary experimental techniques, including solid state 13C NMR, X-ray powder diffraction, differential scanning calorimetry and thermogravimetric analysis. A full model for the decomposition reaction has been elucidated for two polymorphs of DPP- Boc (denoted α- and β-), and the intermediates have been isolated and identified. The crystal structure of β-DPP-Boc was known, but the structure of β-DPP- Boc was unknown. The crystal structure of the β-DPP-Boc has been determined from X-ray powder diffraction data using the Monte Carlo method of structure solution. The structure solution represents the biggest flexible, equal atom structure to be determined from powder diffraction data. A high resolution solid state 13C NMR study has been performed on several derivatives of quinacridone, another successful commercial pigment material, as a means of determining the chemical shielding properties of various carbon environments. The effects of altering packing arrangements, and hence, the electronic distribution around the nuclei, are discussed in detail. The final area of work discussed concerns the study of dynamics of hydrogen bonding in crystalline triphenylmethanol (Ph3COH). The structure of Ph3COH was known, but the locations of the alcohol proton were not found although bond lengths etc. are consistent with hydrogen bonding. This suggests that the hydrogen bonding arrangement is disordered either statically or dynamically. The disorder has been probed experimentally using wide line solid state 2H NMR, and computationally using distributed multipole analysis. Both techniques are particularly sensitive to geometry, and they have been used to develop a dynamic model which agrees well with the experimental 2H NMR data

Synthesis, Properties, and Solid-State Structures of a Series of 6,13-Dicyanoheteropentacene Analogues: Towards New Liquid Crystalline Materials

The focus of this thesis is the synthesis of novel heterocyclic pentacene analogs and the investigation of their self-organization for the development of new materials for organic electronics. The thesis consists of two interrelated projects: the first being development of an improved synthesis of a series of liquid crystalline dicyanotetraoxapentacenes (DCTOPs) while the second entails the exploratory synthesis of several novel dicyanoheteropentacene analogues and a preliminary investigation of their photophysical properties and solid-state structures. Both of these projects centre around the use of nucleophilic aromatic substitution reactions on tetrafluoroterephthalonitrile. Soluble, tetrakis(bis(alkoxy)phenyl)-substituted DCTOPs were originally synthesised via a short synthesis complicated by a tedious purification required in the last step. Despite this, derivatives bearing long alkyl chains were prepared which displayed liquid crystalline properties in addition to aggregation-induced emission. Building upon this success, but with the goal of achieving DCTOPs in an efficient synthetic manner for this thesis, changes were made which eliminated the troublesome fourfold Suzuki coupling by changing the order of reactions, which in turn required a protection-deprotection sequence. Purification in the new synthesis was greatly simplified and the target tetraaryl-DCTOPs were accessed in good overall yields and purities. The synthesis and solid state structures of these DCTOPs are discussed in Chapter 2. Building on the methods developed in Chapter 2, several novel pentacene analogues containing combinations of nitrogen, oxygen, and sulfur atoms installed within the pentacene core were also synthesised. These compounds were prepared in good yields, and preliminary photophysical studies show that all the compounds displayed luminescence in solution and the solid state. It was also shown that replacement of O with N leads to a red shift in absorption and emission spectra. The X-ray crystal structures show that several of these compounds exhibit π−stacking in the solid state, which is an important design element for applications in organic electronics. The synthesis, photophysical properties, and solid-state organization of these novel 6,13-dicyanoheteropentacene analogues are discussed in Chapter 3

Two-Dimensional Self-Assembly Driven by Intermolecular Hydrogen Bonding in Benzodi-7-azaindole Molecules on Au(111)

The control of molecular structures at the nanoscale plays a critical role in the development of materials and applications. The adsorption of a polyheteroaromatic molecule with hydrogen bond donor and acceptor sites integrated in the conjugated structure itself, namely, benzodi-7-azaindole (BDAI), has been studied on Au(111). Intermolecular hydrogen bonding determines the formation of highly organized linear structures where surface chirality, resulting from the 2D confinement of the centrosymmetric molecules, is observed. Moreover, the structural features of the BDAI molecule lead to the formation of two differentiated arrangements with extended brick-wall and herringbone packing. A comprehensive experimental study that combines scanning tunneling microscopy, high-resolution X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and density functional theory theoretical calculations has been performed to fully characterize the 2D hydrogen-bonded domains and the on-surface thermal stability of the physisorbed material

Harnessing Non-Covalent Interactions for Functional Organic Materials

Non‐covalent interactions play a crucial role in developing functional organic materials. As non-covalent interactions are reversible, dynamic and responsive to environment, multifunctional materials with excellent processability and recyclability can be designed and developed utilizing these adaptable forces. In this dissertation, different types of non-covalent interactions were harnessed in developing new functional organic materials which (i) exhibit tunable thermochromism based on the competing charge transfer interactions, (ii) composed of enantiomerically pure macroscopic helices desirable for chiral applications, and (iii) possess conjugated, rigid molecular backbones and regulated intermolecular bonds suitable for extreme operating or processing conditions. The dissertation begins with a brief introduction of different non‐covalent interactions and how they were employed in functional materials. My argument then moves on to examples demonstrating how a variety of non-covalent interactions can be used in developing new functional organic materials. In the first example, a series of donor-acceptor based thermochromic materials were designed and synthesized. These materials can be assembled in water, and solution-processed to form patterns, thin films and aerogels with a reversible thermochromic property. The color transition of donor-acceptor assemblies is resulted from the competing ππ* and n-->π* charge transfer (CT) interactions. To further control the thermochromic properties of these materials, a wide range of -electron rich donors, halogen counterions and -electron poor acceptors have been selected and synthesized. Mechanistic studies to further understand the donor-acceptor self-assembly and color changing processes have also been conducted. Moreover, a facile method to prepare macroscopic helical architectures with controlled handedness was introduced. The feasibility in forming large-scale enantiomerically pure helices and the chiral memory effects of these supramolecular self-assemblies are of great interest for future applications in chiral separation and catalysis. In the last example, conjugated small molecules and a conjugated ladder polymer possessing rigid coplanar backbones and self-complementary intermolecular hydrogen bonds have been developed. The intermolecular π─π interactions and hydrogen bonds of the ladder polymer rendered its excellent resistance to organic solvents, aqueous acids, and thermal treatments. This unique property allows for developments of robust polymer materials for applications associated with extreme operating or processing conditions

Evaluation of Thermal Effects and Lattice Vibrations in Molecular Crystals

The effect of temperature plays a large role in the behavior of many physical systems. While it is certainly the case that many effects of temperature can be observed macroscopically, they are often of molecular origin, and determining why these effects occur can provide insight into the nature of chemical systems as a whole. A large portion of this work is dedicated to analyzing polymorphic forms and small organic molecules with interesting thermal effects. Low-frequency spectroscopy is a very useful tool in the investigation of polymorphs, providing a method of probing a sample to investigate the possible motions and characteristics that these systems exhibit with the effect of heating or cooling. In this work, low-frequency spectroscopy is combined with X-ray diffraction to differentiate polymorphs and analyze systems that behave anharmonically with temperature. This experimental work is complemented with solid-state density functional theory calculations, enabling for the evaluation of the energetics of the studied systems, providing insight into the relative stabilities of the studied systems over a range of temperatures, and can even elucidate the mechanisms by which polymorphic transformations may occur. Overall, this is an achievement in the understanding of thermal effects in crystalline systems made possible by the combination of experimental and theoretical techniques

Novel synthetic approach to heteroatom doped polycyclic aromatic hydrocarbons: Optimizing the bottom-up approach to atomically precise doped nanographenes

The success of the rational bottom-up approach to nanostructured carbon materials and the discovery of the importance of their doping with heteroatoms puts under the spotlight all synthetic organic approaches to polycyclic aromatic hydrocarbons. The construction of atomically precise heteroatom doped nanographenes has evidenced the importance of controlling its geometry and the position of the doping heteroatoms, since these parameters influence their chemical–physical properties and their applications. The growing interest towards this research topic is testified by the large number of works published in this area, which have transformed a once “fundamental research” into applied research at the cutting edge of technology. This review analyzes the most recent synthetic approaches to this class of compounds

Autoxidation of 4-Hydrazinylquinolin-2(1H)-one; Synthesis of Pyridazino[4,3-c:5,6-c′]diquinoline-6,7(5H,8H)-diones

An efficient synthesis of a series of pyridazino[4,3-c:5,6-c′]diquinolines was achieved via the autoxidation of 4-hydrazinylquinolin-2(1H)-ones. IR, NMR (1H and 13C), mass spectral data, and elemental analysis were used to fit and elucidate the structures of the newly synthesized compounds. X-ray structure analysis and theoretical calculations unequivocally proved the formation of the structure. The possible mechanism for the reaction is also discussed

Autoxidation of 4-Hydrazinylquinolin-2(1H)-one; Synthesis of Pyridazino[4,3-c:5,6-c′ ]diquinoline-6,7(5H,8H)-diones

An efficient synthesis of a series of pyridazino[4,3-c:5,6-c′]diquinolines was achieved via the autoxidation of 4-hydrazinylquinolin-2(1H)-ones. IR, NMR ($^1$H and $^13$C), mass spectral data, and elemental analysis were used to fit and elucidate the structures of the newly synthesized compounds. X-ray structure analysis and theoretical calculations unequivocally proved the formation of the structure. The possible mechanism for the reaction is also discussed