Porphyrinic Dyads and Triads Assembled around Iridium(III) Bis-terpyridine: Photoinduced Electron Transfer Processes Isabelle M. Dixon, § Jean-Paul Collin,* ,§ Jean-Pierre Sauvage,* ,§ and Lucia Flamigni* ,‡ Laboratoire de Chimie Organo-Mine ´rale, UMR 7513 CNRS, Universite ´ Louis Pasteur, Institut Le Bel, 4, rue Blaise Pascal, 67070 Strasbourg, France, and Istituto FRAE-CNR, Via P. Gobetti 101, 40129 Bologna, Italy ReceiVed April 17, 2001 Multicomponent arrays based on a central iridium(III) bis-terpyridine complex (Ir) used as assembling metal and free-base, zinc(II) or gold(III) tetraaryl-porphyrins (PH 2 , PZn, PAu) have been designed to generate intramolecular photoinduced charge separation. The rigid dyads PH 2 -Ir, PZn-Ir, PAu-Ir, and the rigid and linear triads PH 2 -Ir-PAu, PZn-Ir-PAu, as well as the individual components Ir, PH 2 , PZn, PAu have been synthesized and characterized by various techniques including electrochemistry. Their photophysical properties either in acetonitrile or in dichloromethane and toluene have been determined by steady-state and time-resolved methods. In acetonitrile, excitation of the triad PH 2 -Ir-PAu leads to a charge separation with an efficiency of 0.5 and a resulting charge-separated (CS) state with a lifetime of 3.5 ns. A low-lying triplet localized on PH 2 and the presence of the heavy Ir(III) ion offer the CS state an alternative deactivation path through the triplet state. The behavior of the triad PZn-Ir-PAu in dichloromethane is rather different from that of PH 2 -Ir-PAu in acetonitrile since the primary electron transfer to yield PZn + -Ir - -PAu is not followed by a secondary electron transfer. In this solvent, both unfavorable thermodynamic and electronic parameters contribute to the inefficiency of the second electron-transfer reaction. In contrast, in toluene solutions, the triad PZn-Ir-PAu attains a CS state with a unitary yield and a lifetime of 450 ns. These differences can be understood in terms of ground-state charge- transfer interactions as well as different stabilization of the intermediate and final CS states by solvent. Introduction Artificial photosynthesis has been a very active area of research for more than 3 decades, with the elaboration and study of models of natural systems or of synthetic devices aimed at converting light energy into chemical or electrical energy. An important source of inspiration has been the disclosure of the structure of bacterial photosynthetic Reaction Centers (RC). 1 In the past 20 years, many light-triggered charge separation molecular systems have been designed to mimick the processes taking place in the RC. 2 Porphyrins have been used as components of such devices since the very beginning, due to their resemblance with natural components and due to the fact that the redox and spectroscopic properties of these chro- mophores can be widely varied by the use of electroactive or bulky substituents and by their coordination to different transi- tion metals. 3 In the models elaborated by the Strasbourg group in the course of the past decade, a free-base or zinc(II) porphyrin is used as chromophore and primary electron donor, while a gold(III)- metalated porphyrin serves as electron acceptor. 4 In a modular strategy, 5 the electro-active components are assembled around an octahedral transition metal complex of the bis-terpyridine type, allowing the construction of linear triads with fixed intercomponent distances. 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