Photo-Active Metal Complexes

The photochemistry of metal complexes has been extensively studied since the 1960s and has been the subject of a number of monographs and reviews [1,11,14-19]. Systematic investigations have concentrated on or d  

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Finally these compounds may also present in the future some interest in the area of novel anti-tumor drugs, or in photochemotherapy [12], Up to now the mechanism of action of the Pt complexes as antineoplastic agents has been extensively examined [13]. In spite of their successful applications, there is a need in compounds that are less toxic than the Pt derivatives. Therefore novel photo-active metallic compounds could offer future possibilities for cancer treatment. The fact that a drug would become active exclusively under illumination might represent an advantage. 

Polynuclear complexes, molecular dyads, triads, and other supermolecules composed of redox- and photo-active metal polypyridine units have a great promise as components of future molecular electronic or photonic devices as optical switches, relays, memories, etc. [38, 46],... 

Substitution-inert complexes have also recently been introduced into DNA as modified-base phosphoramidites. Interest here is generally focused on photo- and redox-active metal species for use as probes for sensing applications (165) and in studies on DNA-mediated electron... 

The insertion of a photosensitive group or of a redox active unit into the push-pull system 1 yields switchable molecular wires and push-pull molecules that contain a photo-switch or a redox switch S, as represented in 4. Compounds of such type containing for instance electroactive ferrocene groups and photosensitive metal complexes, have been synthesized. Some of them are shown in series 5 (Marczinke, B. Przibilla, K.J. Lehn, J.-M., unpublished data). 

Currently, metal-polypyridine units are the molecular building blocks of choice whenever a compound with special electro- and/or photo-activity is to be designed. The research emphasis has somewhat shifted from fundamental studies of electron transfer reactivity and excited state properties of individual complexes to the design of new functional molecules and supermolecules with predetermined properties. 

In case 1.3 the pro-catalyst interacts with the substrate (for example by photosubstitution) to generate the actual catalyst. Such a case is germane to photo-induced electron transfer catalyzed reactions [7] shown in case 1.4. Here, an excited state of a transition metal complex (designated as I) could interact with the substrate by a positive or negative electron transfer. Because of the activation induced by electron transfer [13] S would be transformed into S, whose fate is to be regenerated one or several steps after yielding P. 

The discovery and coordination chemistry of phenanthrolines closely followed that of the bipyridines throughout the early twentieth century, much as it does today. F. Blau1 and Gerdiessen2 are credited with the earliest published syntheses of 1,10-phenanthrolines (phen, (1)) in the late nineteenth century. While the colored metal complexes of these compounds had been reported, their utility as colorimetric indicators was not discussed until 1931.3 For the next several decades, phenanthroline derivatives served primarily as colorimetric indicators for many transition metals. Throughout this period, the contributions of G. F. Smith,4-7 F. H. Case,8-10 A. A. Schilt,11 and others toward the chemistry of these complexes resulted in a wealth of synthetic routes for derivatives of (1). The flourishing studies of polypyridyl-coordinated metal complexes provided inspiration for preparing unique phenanthrolines with a wealth of pendant photo- and electro-active molecules.12-16... 

Magnetic interactions of a paramagnetic metal center and a free radical ligand are of interest for the development of new types of molecular magnetic materials. Complexes of this type (such as (83)) change their magnetic properties upon irradiation by visible light and can serve as a basis for development of novel photo-activated memory units for electronic devices.346,347... 

Electron transfer is an appealing process allowing the same transformation as in photochemistry, i.e., cyclization-reopening. In this context, the DTE unit has proven to be useful for the elaboration of photo and/or electrochromic metal-based systems specially devoted to the control of the electronic communication in bimetallic complexes. Organometallic complexes crmsisting of Jt-conjugated system bridging two redox active metal centers have proven to be efficient molecular wires (Fig. 11). 

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