Designed intramolecular competition in a chromophore-biquencher complex

Competitive energy and electron transfer occur following excitation of the chromophore-biquencher [Re-1(MebpyCH(2)OCH(2)An)(CO)(3)(MQ(+))](PF6)(2)(MebpyCH(2)OCH(2)An is 4-[(9-anthrylmethoxy)methyl]-4'-methyl-2,2'-bipyridine; MQ(+) is N-methyl-4,4',-bipyridinium ion). Following excitation with a 392-nm, 4-ns laser pulse in 1,2-dichloroethane (DCE), the initial excited state energy is distributed in a similar to 2:1 ratio between (3)An* and the lower lying Re-II(MQ(.)) metal-to-ligand charge transfer (MLCT) excited state. The appearance of the two states was monitored by transient absorption spectroscopy, which detected the triplet-triplet band for (3)An* at lambda(max) = 420 nm (tau = 35 +/- 2 mu s, k = (2.9 +/- 0.2) x 10(4) s(-1)) and a pi --> pi* band of MQ(.) at 610 nm (tau = 37 +/- 2 ns, k = (2.7 +/- 0.2) x 10(7) s(-)1). These states result from a competitive partitioning in the initial excited state or states. They do not interconvert to any significant degree on the time scale of the shorter lived, higher energy Re-II(MQ*) state.