MacLean, Elizabeth Janet; (1997) Structure, dynamics and thermal reactivity of pigments and other organic solid. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

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.

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