Photoinduced Electron Transfer in Iridium(spacer)pyridinium Complexes

• Published in: Journal of physical chemistry (1952) 1994-05, Vol.98 (20), p.5176-5179
• Main Authors: Farid, Ramy S, Chang, I-Jy, Winkler, Jay R, Gray, Harry B
• Format: Article
• Language: English
• Subjects: 400102 - Chemical & Spectral Procedures; 400201 - Chemical & Physicochemical Properties; 400500 - Photochemistry; 990200 - Mathematics & Computers; ABSORPTION SPECTROSCOPY; ACETONITRILE; CHEMICAL REACTIONS; COMPILED DATA; COMPLEXES; DATA; DISPERSIONS; ELECTRON TRANSFER; ENERGY; FLUORESCENCE; FREE ENERGY; GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE; INFORMATION; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; IRIDIUM COMPLEXES; LUMINESCENCE; MAGNETIC RESONANCE; MATHEMATICAL MODELS; MIXTURES; NITRILES; NUCLEAR MAGNETIC RESONANCE; NUMERICAL DATA; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; ORGANOMETALLIC COMPOUNDS; PHOTOCHEMICAL REACTIONS; PHYSICAL PROPERTIES; RESONANCE; SOLUTIONS; SPECTROSCOPY; THERMODYNAMIC PROPERTIES; TRANSITION ELEMENT COMPLEXES
• ISSN: 0022-3654; 1541-5740
• DOI: 10.1021/j100071a001

Photoinduced electron-transfer (ET) reactions in a series of iridium(spacer)pyridinium complexes, [Ir([mu]-pz*)-(CO)PH[sub 2]POC[sub 6]H[sub 4](CH[sub 2])[sub n]-A[sup +]][sub 2] (pz* = 3,5-dimethylpyrazolyl; Ph = C[sub 6]H[sub 5]; C[sub 6]H[sub 4] = phenylene: A[sup +] pyridinium (py[sup +]) or substituted py[sup +]; n = 0-3), have been studied in acetonitrile solution at room temperature. The rates of singlet ([sup 1]Ir[sub 2]* [yields] A[sup +]; [sup 1]ET) reactions were determined for each complex, and for n = 1 and 2 species, the rates of thermal charge recombination (ET[sup b]) also were measured. The ET rates for the n = 1 system display a Gaussian free-energy dependence ([lambda] = 1.0 eV, H[sub AB] = 5 cm[sup [minus]1]). With one exception, maximum ET rates exhibit an exponential dependence upon the number of carbon atoms ([alpha][sub C]) in the spacer. The exception is the n = 1 ([alpha][sub C] = 5) system; k[sub max] is almost a factor of 100 slower than predicted by the exponential dependence on [alpha][sub C], indicating that donor-acceptor electronic coupling through a single methylene link is unusually weak. 33 refs., 3 figs., 2 tabs.