The development of ionophores offering alternative modes of transduction of cation inclusion has evoked much recent interest. The first four chapters of this thesis deal with one such set of ionophores, namely chromogenic calix[4]arenes, which can exhibit a significant change in optical properties upon complexation with metal cations in the presence of a suitable base. All of the chromogenic compounds examined are ionisable chromoionophores which rely on the deprotonation of a phenolic group for colour generation. Chapter 1:- This chapter offers a comprehensive introduction to ionophores with particular attention being paid to chromoionophores. Chapter 2:- This chapter outlines the methods and materials used in the examination of the novel chromogenic calixarenes. Chapter 3:- This chapter describes four novel calix[4]arenes bearing either one or four nitrophenol chromogenic groups. All compounds were examined as cation selective ionophores capable of exhibiting significant colour changes u p o n complexation with Li+, and to a lesser extent with N a +, in the presence of a suitable base. Chapter 4:- This chapter concentrates on assessing another series of novel chromogenic calix[4]arenes bearing from one to four nitrophenylazophenol chromophores as optical signalling moieties. Li+ selectivity over Na+ was again exhibited. The lithium complex of the tetranitrophenylazophenol ligand was additionally examined as a solid phase gaseous trimethylamine ( T M A ) indicator. Chapte r 5:- This chapter deals with novel solid-state ion-selective electrodes. Both coated wire electrodes ( C W E ) and solid contact (SC) electrodes, which combined the electronically conducting nature of electropolymerised polythiophene (PT) of polyoctylthiophene ( P O T ) with an ionically conducting PVC/ionophore layer, were assessed as lithium- and chloride-selective electrodes. Hybrid-film electrodes ( H F E ) which were made by mixing chemically polymerised P O T and a PVC/ionophore cocktail in T H F and applying this mixture to a glassy carbon substrate were also examined as Li+ selective electrodes.