Applications of functionalized transition metal complexes in photonic and optoelectronic devices

Transition metal complexes with low lying excited states are finding increa sing use as photosensitizers. Major work horses are those derived from poly pyridine complexes and metalloporphyrins. The low-lying metal-to-ligand cha rge transfer (MLCT) and ligand-centered (pi-pi*) excited states of these co mplexes are fairly long-lived to participate in electron transfer processes . The emissive nature and high quantum yields allow development of applicat ions. In this paper we review some of the recent applications of these coor dination complexes in photochemical systems for the direct conversion and s torage of solar energy. Mesoporous membrane type films with large surface a rea 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 photoelectrochemic al solar cells, intercalation batteries, optical display and optical sensor s. Principles of operation of these optoelectronic devices are reviewed her e. 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 th e dye-sensitized solar cells and associated mechanistic studies. Principles of operation of electrochromic and photoelectroluminescent devices based o n anchored polypyridine complexes of Ru are also indicated. (C) 1998 Elsevi er Science S.A. All rights reserved.