SUPRAMOLECULARA ASSEMBLIES OF METAL-COMPLEXES - LIGHT-INDUCED ELECTRON-TRANSFER IN THE GALLERIES OF ALPHA-ZIRCONIUM PHOSPHATE

Rapid photoinduced electron transfer was observed with supramolecular assemblies of donor and acceptor metal complexes at the galleries of n -butylammonium salt of alpha-zirconium phosphate ((C4H9NH3)(2)Zr(PO4)( 2). xH(2)O, abbreviated as BAZrP). Tris(2,2'-bipyridyl)ruthenium(II)2( +) luminescence, for example, was quenched by tris(2,2'-bipyridyl)coba lt(III)(3+) with rate constants exceeding 1.6 x 10(12) m(2) mol(-1) s( -1), when the metal complexes were intercalated in the galleries of BA ZrP. The quenching rates were unaffected when the viscosity of the BAZ rP suspensions was increased (2.1 mixture of ethylene glycol-water) or when the loading of the donor was increased 10-fold. Even when cooled to 77 K, as a rigid glass, the electron transfer reactions between th e donor and the acceptor proceed at essentially the same rate as at ro om temperature indicating a very low activation energy for the electro n transfer reaction. These activation-less rate constants are faster t han anticipated for diffusion controlled electron transfer rates at BA ZrP galleries, at low temperatures. Excited-state energy migration fro m donor to donor (antenna effect) followed by electron transfer betwee n the nearest donor-acceptor pairs is one explanation proposed to acco unt for the above observations.