Iridium Terpyridine Complexes as Functional Assembling Units in Arrays for the Conversion of Light Energy
- 11 June 2008
- journal article
- Published by American Chemical Society (ACS) in Accounts of Chemical Research
- Vol. 41 (7), 857-871
- https://doi.org/10.1021/ar700282n
Abstract
In photosynthesis, sunlight energy is converted into a chemical potential by an electron transfer sequence that is started by an excited state and ultimately yields a long-lived charge-separated state. This process can be reproduced by carefully designed multicomponent artificial arrays of three or more components, and the stored energy can be used to oxidize or reduce molecules in solution, to inject electrons or holes, or to create an electron flow. Therefore, the process is important both for artificial-photosynthesis research and for photovoltaic and optoelectronic applications. Molecular arrays for photoinduced charge separation often use chromophores that resemble the natural ones. However, new synthetic components, including transition metal complexes, have had some success. This Account discusses the use of bis-terpyridine (tpy) metal complexes as assembling and functional units of such multicomponent arrays. M(tpy)2(n+) complexes have the advantage of yielding linear arrays with unambiguous geometry. Originally, Ru(tpy)2(2+) and Os(tpy)2(2+) were used as photosensitizers in triads containing typical organic donors and acceptors. However, it soon became evident that the relatively low excited state of these complexes could act as an energy drain of the excited state of the photosensitizer and, thus, seriously compete with charge separation. A new metal complex that preserved the favorable tpy geometry and yet had a higher energy level was needed. We identified Ir(tpy)2(3+), which displayed a higher energy level, a more facile reduction that favored charge separation, a longer excited-state lifetime, and strong spectroscopic features that were useful for the identification of intermediates. Ir(tpy)2(3+) was used in arrays with electron-donating gold porphyrin and electron-accepting free-base porphyrins. A judicious change of the free-base porphyrin photosensitizer with zinc porphyrin allowed us to shape the photoreactivity and led to charge separation with unity yield and a lifetime on the order of a microsecond. In a subsequent approach, an Ir(tpy)2(3+) derivative was connected to an amine electron donor and a bisimide electron acceptor in an array 5 nm long. In this case, the complex acted as photosensitizer, and long-lived charge separation over the extremities (>100 micros, nearly independent of the presence of oxygen) was achieved. The efficiency of the charge separation was modest, but it was improved later, after a modification aiming at decoupling the donor and photosensitizer components. This study represents an example of how the performances of an artificial photofunctional array can be modeled by a judicious design assisted by a detailed knowledge of the systems.Keywords
This publication has 24 references indexed in Scilit:
- Photocatalytic Generation of Hydrogen from Water Using a Platinum(II) Terpyridyl Acetylide ChromophoreJournal of the American Chemical Society, 2006
- Autonomous artificial nanomotor powered by sunlightProceedings of the National Academy of Sciences of the United States of America, 2006
- Light Induced Manganese Oxidation and Long-Lived Charge Separation in a Mn2II,II−RuII(bpy)3−Acceptor TriadJournal of the American Chemical Society, 2005
- Chemical Approaches to Artificial Photosynthesis. 2Inorganic Chemistry, 2005
- Platinum Chromophore-Based Systems for Photoinduced Charge Separation: A Molecular Design Approach for Artificial PhotosynthesisInorganic Chemistry, 2005
- Mimicking Photosynthetic Solar Energy TransductionAccounts of Chemical Research, 2000
- Photoinduced electron transfer in supramolecular systems for artificial photosynthesisChemical Reviews, 1992
- Photoinduced processes in dyads and triads containing a ruthenium(II)-bis(terpyridine) photosensitizer covalently linked to electron donor and acceptor groupsInorganic Chemistry, 1991
- Photochemically induced charge separation at the molecular level. A chromophore-quencher complex containing both an electron donor and an acceptorJournal of the American Chemical Society, 1987
- Hydrogen Evolution from Water by Visible Light, a Homogeneous Three Component Test System for Redox CatalysisHelvetica Chimica Acta, 1978