Phthalocyanine dimers and PIMs based on hexaphenylbenzene

• Main Author: Short, Rhys Bryan
• Published: Cardiff University 2011
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.585213

The first part of the work, described in Chapter One, concentrates on the attempted synthesis of discrete, water-soluble phthalocyanine dimers, which were of interest as model compounds for studies into the photochemical stability of phthalocyanine dyes. The phthalocyanines were linked together by two different bridges derived from diethyl 3,3-bis(4-(3,4- dicyanophenoxy)phenyl)pentanedioate and 1,2-di(4'-(3",4"-dicyano)phenoxy)-3,4,5,6- tetraphenyl-benzene. The formation of the dimers using 4-(2,6-di-/so- propylphenoxy)phthalonitrile was possible, as determined by mass spectrometry and visible absorption spectroscopy of the crude product mixture, but their isolation proved extremely difficult and so this work was abandoned to concentrate on the work described in chapters 3-4. After an introduction to the research area of organic microporous materials (Chapter 2) and a statement of the new aims and objectives, the second part of the work, described in Chapter 3, concerns the use of hexaphenylbenzene as a structural unit for the synthesis of polymers of intrinsic microporosity, PIMs. Even though hexaphenylbenzene does not have a site of contortion, typical of PIMs, it was thought that the rigidity and non-planarity of this unit due to the lack of rotational freedom of the benzene rings would hinder efficient packing of the polymer in the solid state and induce intrinsic microporosity. A number of different hexaphenylbenzene-based monomers suitable for use in the type of polymerisation reactions used to make PIMs due to their catechol units were synthesised. It was discovered that the position of the catechol substituents in relation to one another had a significant effect on the molecular mass and hence physical properties of the polymer, in particular its ability to form self-standing films. It can be concluded that placing the catechol units on opposite sides of the hexaphenylbenzene unit (para-substitution) suppressed cyclic oligomer formation and allowed the preparation of polymers of high molecular mass with good film-forming properties. In addition, the microporosity of this polymer was greater than that obtained from the monomer in which the catechol units were placed adjacent to one another (ortho-substitution). The Preface resulting self-standing films allowed the measurement of gas permeation through this polymer, which showed encouraging performance. The crystal packing properties of the monomers and a 2+2 cyclic oligomer isolated from the polymerisation reaction using the monomer with adjacent catechol units on the hexaphenylbenzene core are described in Chapter 4. The macrocyclic 2+2 cyclic oligomer is highly fluorescent and its binding with nitrobenzene, as a model for small nitrated aromatic compounds, was investigated in the context of its possible use as a sensor. However, studies offered no evidence of selective binding. Finally, Chapter 5 offers suggestions on the concept of using hexaphenylbenzene units in flow chemistry.