ChemInform Abstract: Iridium Terpyridine Complexes as Functional Assembling Units in Arrays for the Conversion of Light Energy
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.
- SourceAvailable from: Hadi Amiri Rudbari
Main Group Chemistry 11/2013; 12 (2013):349–360. · 0.65 Impact Factor
- "The coordination chemistry of multidentate ␣-terpyridine-based ligands (tpy) is interesting because of their application in emitters for electroluminescence devices and in molecular probes for biochemical research      . Along with the structural features, these ligands and their complexes have interesting electrochemical , catalytic and optical properties   . "
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ABSTRACT: Two triads (i.e., 3PTZ–Pt–MNDI and 10PTZ–Pt–MNDI) consisting of 3-phenothiazine (3PTZ) or 10-phenothiazine (10PTZ), bipyridine–diacetylide platinum complex (Pt), and naphthalene diimide (MNDI) chromophores linked by highly twisted biphenylene spacers have been prepared. The formation and decay of the charge-separated (CS) states in toluene were studied by use of picosecond and nanosecond laser photolysis via selective excitation of the Pt moiety. The time required for formation of the CS state, PTZ+–Pt–MNDI−, from PTZ–3Pt*–MNDI was determined to be τ CS = 280 ps for 3PTZ+–Pt–MNDI− and τ CS = 230 ps for 10PTZ+–Pt–MNDI−. The lifetimes of the CS states were determined to be τ CR1 = 75 ns (95 %) and τ CR2 = 285 ns (5 %) for 3PTZ+–Pt–MNDI− and τ CR = 830 ns for 10PTZ+–Pt–MNDI−. Formation and decay of the CS states are discussed in terms the Marcus theory and the spin-correlated radical pair mechanism.Research on Chemical Intermediates 01/2012; 39(1). DOI:10.1007/s11164-012-0642-6 · 1.54 Impact Factor
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ABSTRACT: The kinetics for photoinduced charge separation and thermal charge-recombination processes in three donor–bridge–acceptor molecules with rhenium(I) tricarbonyl diimine photosensitizers were investigated. Time resolved luminescence and transient absorption spectroscopies reveal that in addition to driving force effects, differences in bridge-mediated electronic donor–acceptor coupling among the three dyads play important roles. Notably, it is seen that charge separation depends strongly on whether initial photoexcitation involves promotion of an electron towards or away from a phenothiazine electron donor. Thermal charge recombination rates are found to differ by a factor of 2 between two isomeric dyads due to an electronic coupling effect.Inorganica Chimica Acta 02/2009; 362(10). DOI:10.1016/j.ica.2009.01.040 · 2.04 Impact Factor