Electron tunneling through water:: Oxidative quenching of electronically excited Ru(tpy)22+ (tpy=2,2′:6,2"-terpyridine) by ferric ions in aqueous glasses at 77 K

The luminescence lifetime of Ru(tpy)(2)(2+) (tpy = 2,2':6,2 "-terpyridine) is 8.0 mu s in H2SO4/H2O and HSO3F/H2O glasses (25% v/v) at 77 K, and 10.2 mu s in D2SO4/D2O (25% v/v). Addition of moderate concentrations of the powerfully oxidizing Fe(OH2)(6)(3+) ion to the glasses leads to accelerated and highly nonexponential *Ru(tpy)(2)(2+) decay kinetics. The quenching is attributed to electron transfer from *Ru(tpy)(2)(2+) to randomly dispersed Fe(OH2)(6)(3+) complexes. The luminescence decay kinetics and quantum yields in the three aqueous glasses indicate that the electron-transfer rate constants decrease from similar to 10(13) s(-1) at van der Waals contact with an exponential distance decay constant of 1.68 +/- 0.07 Angstrom(-1).