The preparation of new functionalised phthalocyanine compounds has been the subject of intense research over the last three decades in order to develop new commercial applications. Interestingly, their electrical and physical properties can be tuned by suitable derivatization of their rigid inner core. A brief summary of the syntheses, properties and applications of these compounds is described in Chapter 1. The aim of this project was to synthesise new phthalocyanines for use in field effect transistors (FETs). Chapter 2 describes the investigation of the preparation of novel polysiloxane phthalocyanine polymers having hexyl substituents in non-peripheral positions. It has been shown that polysiloxanes comprising non-peripherally substituted phthalocyanines of this type cannot be isolated. Further investigation indicates that this is likely to be due to steric hindrance. A series of mixed oligomeric compounds were successfully synthesised by condensation of the corresponding substituted and unsubstituted silicon phthalocyanine monomers. These co-oligomeric materials were functionalised, isolated and characterised and found to exhibit interesting optical properties. Moreover, the solid-state structure of a mixed phthalocyanine dimer was determined by X-ray diffraction analysis. Interestingly, red fluorescence emission was also exhibited by derivatives of these compounds. During the preparation of a phthalocyanine intermediate, an unexpected coloured sideproduct was also observed. The structure of this product proved to be closely related to the phthalocyanine and was characterised as a tetrabenzotriazaporphyrin. The origin of this by-product was explored. A series of metal-free and metallated derivatives of this compound was subsequently prepared and their optical and physical properties compared to their corresponding phthalocyanines. The results of these investigations are reported in Chapter 3.