Photoinduced electron-transfer (ET) reactions in a series of iridium(spacer)pyridinium complexes. [Ir(μ-pz*)-(CO)PH2POC6H4(CH2)n-A+] 2 (pz* = 3,5-dimethylpyrazolyl; Ph = C6H5; C6H4 = phenylene: A+ pyridinium (py+) or substituted py+; n = 0-3), have been studied in acetonitrile solution at room temperature. The rates of singlet (1Ir2* → A+; 1ET) reactions were determined for each complex, and for n = 1 and 2 species, the rates of thermal charge recombination (ETb) also were measured. The ET rates for the n = 1 system display a Gaussian free-energy dependence (λ = 1.0 eV, HAB = 5 cm-1). With one exception, maximum ET rates exhibit an exponential dependence upon the number of carbon atoms (αC) in the spacer. The exception is the n = 1 (αC = 5) system; kmax is almost a factor of 100 slower than predicted by the exponential dependence on αC, indicating that donor-acceptor electronic coupling through a single methylene link is unusually weak.
ASJC Scopus subject areas
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