The world of organic luminophores has been confined for a long time to fairly standard biological labeling applications and to certain analytical tests. Recently, however, the field has undergone a major change of direction, driven by the dual needs to develop novel organic electronic materials and to fuel the rapidly emerging nanotechnologies. Among the many diverse fluorescent molecules, the Bodipy family, first developed as luminescent tags and laser dyes, has become a cornerstone for these new applications. The near future looks extremely bright for "porphyrin's little sister".

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Metal oxides, in the form of dispersed powders, have been tested as potential catalysts for the four-electron oxidation of water to 0, under photochemical conditions. The most efficient catalysts were found to be IrO,, Co,O,, RuO,, NiCo,O,, Rh,O, and Mn,O, and, in particular, high activity was observed with IrO,. Comparison of the oxide structure with its observed rate of 0, generation under standard conditions has allowed formulation of a few general requisites for an effective catalyst. Samples of iridium oxide deposited onto the surface of a second (inert) oxide were tested for their 0,-evolving capability. The efficiency of the system depended markedly upon the nature of the support. Materials that favour formation of small deposits of iridium oxide (e.g. ZnO, MgO, TiO,) are the best supports, whilst 0, production is almost completely inhibited with acidic supports. Many metal oxides can be prepared in the form of hydrates of variable composition. These materials also function as 0,-evolving catalysts, the efficiency of the process depending upon any thermal pretreatment. This finding is explained in terms of changes in structure and composition of the oxide that occur upon heating.As part of a protracted research programme, concerned with building a photosystem capable of storing solar energy via the photodissociation of water, a range of 0,-evolving catalysts has been developed. 1-6 Mostly, these catalysts have contained ruthenium dioxide in some form, and all have been prone to corrosion under high anodic bias. homogeneous,'^ colloidal5* and heterogeneou~l.~ Ru0,-based catalysts have been tested for their 0,-evolving capacities under photochemical conditions. In certain cases, quite high efficiencies have been reported. Despite such detailed studies, the poor performance of the catalyst remains as the most serious obstacle in developing a suitable anodic branch of a solar-energy storage device and, if a satisfactory catalyst is to be identified, attention should be given to materials other than RuO,. Indeed, it has been shown that Ir0,,lo Pt0210 and MnO," powders will function as heterogeneous catalysts for water oxidation in related model systems.Using a well established photochemical test system,6 we have evaluated the 0,-evolving capabilities of a range of metal oxides. These materials have been used in the form of powders suspended in aqueous solution. Most of the materials were found to be inferior to RuO, powders, but a few oxides, notably IrO,, were effective catalysts for water oxidation and demonstrated much higher levels of corrosion resistance than the catalysts used previously. Several of these oxides exist in the form of hydrates for which the 0,-evolving capability is increased upon dehydration. In order to extend the scope of the work, a series of catalysts was prepared in which IrO, was deposited onto the surface of a second (inert) oxide. By this means, the effect of the supporting agent on the 2795

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