Applications of functionalized transition metal complexes in photonic and optoelectronic devices

Transition metal complexes with low lying excited states are finding increasing use as photosensitizers. Major work horses are those derived from polypyridine complexes and metalloporphyrins. The low-lying metal-to-ligand charge transfer (MLCT) and ligand-centered (pi-pi*) excited states of these complexes are fairly long-lived to participate in electron transfer processes. The emissive nature and high quantum yields allow development of applications. In this paper we review some of the recent applications of these coordination complexes in photochemical systems for the direct conversion and storage of solar energy. Mesoporous membrane type films with large surface area can be prepared from nanosized colloidal semiconductor dispersions. By suitable molecular engineering, the metal complexes can be readily attached to the surface. These films with anchored complexes are finding increasing use in energy conversion devices such as dye-sensitized photoelectrochemical solar cells, intercalation batteries, optical display and optical sensors. Principles of operation of these optoelectronic devices are reviewed here. Various approaches to anchoring molecules on surfaces are first reviewed followed by an overview of the methods of preparation of mesoporous films. This is followed by a comprehensive discussion of the design details of the dye-sensitized solar cells and associated mechanistic studies. Principles of operation of electrochromic and photoelectroluminescent devices based on anchored polypyridine complexes of Ru are also indicated. (C) 1998 Elsevier Science S.A. All rights reserved.