Photoreversible metal chelating agents.

The main objective of this work has been to design and synthesise new photoreversible metal chelating agents. The reversibility is effected mainly by using light as a switch to isomerise two forms of a chelating agent, (1↔2), where R2 is a metal complexing group. Highlighted in this thesis is the problem of why some compounds show limited photoreversible and chelating properties and therefore the need to tune the systems to compensate for the shift in photodynamic equilibria caused by the inherent stabilisation of the chelated form by the process of co-ordination. By strategically placing substituents (i.e. electronic tuning) on the crowned indolospirobenzopyran rings, chelating ability can be tuned to obtain photoreversible binding agents. However thermal equilibration of the systems was observed and there was a need for development of systems with larger energy barriers between the various photoisomers and therefore, sterically restricted photochromic systems have been examined as a means for controlling the photochromic (and hence metal chelating) process. A demonstration that photoreversible chelating agents can be used to transport ions through a membrane under photochemical control has been made