Molten salts of Ni(bpy(350))(3)(2+) and single stranded oligonucleotides were prepared (bpy(350) = 4,4'-(CH3(OCH2CH2)(7.24)OCO)(2)-2,2'-bipyridine). Photoinduced electron transfer was observed between small amounts of Ru(bpz)(3)(2+)* (E2+*(/1+) = 1.35 V vs SCE, bpz = 2,2'-bipyrazine) added to the melt and guanine in the nucleic acid, by measuring the emission lifetime of the ruthenium complex in melts containing varying amounts of guanine-containing nucleic acid. Electrochemically determined diffusion coefficients in these media were <1 x 10(-11) cm(2)/s, showing that the Ru(bpz)(3)(2+)* diffuses less than 0.4 Angstrom during the measured excited-state lifetime. A linear relationship was observed between the fraction of Ru(bpz)(3)(2+)* that was quenched (calculated as (taudegrees - tau)/tau) and the mole fraction of guanine-containing oligonucleotides. This relationship supports a quenching mechanism that does not involve diffusion of the ruthenium complex. The average electron-transfer rate constant at full guanine loading was 7 x 10(6) s(-1), which implies an average electron-transfer distance of 12.5 Angstrom (center-to-center).