Interaction of tris(2,2'-bipyridine)ruthenium(II) dichloride (Ru(b~y)3~+) with n-butylammonium salt of a-Zirconium phosphate (BAZrP) causes extensive red shifts of the metal-to-ligand charge-transfer (MLCT) absorption band of the metal complex (from 452 to 480 nm). In contrast, the luminescence maximum is blue shifted, from 610 nm in aqueous media, to 580 nm when the metal complex was bound to BAZrP. Such a blue shift in the emission was observed when R~(bpy)3~+ was present in rigid matrices such as ice, or ethanolmethanol glasses at low temperature. Therefore, the microenvironment surrounding the metal complex in BAZrP is rigid and does not permit the relaxation of the initially produced metal-to-ligand charge-transfer (MLCT) excited state even at room temperature. Upon binding to the zirconium phosphate, the emission yield of R~(bpy)3~+ is increased nearly 5-fold when compared to aqueous solutions. Such large increases in the emission were not observed with Ru(bpy)32+ in other heterogeneous media. The absorption and emission spectral maxima are independent of loading of the metal complex, strongly suggesting the formation of islands or pools of these metal complexes at the interlayer regions of BAZrP. The luminescence intensities decrease with loading of the metal complex indicating the strong self quenching of the luminescence within these pools. Stern-Volmer plots were constructed from the steady-state data and the estimated KSV value was 1.1x lo6 m2/mol. Powder X-ray diffraction patterns of the samples indicate that intercalation of Ru(bpy)32+into BAZrP increases the interlayer separation from 18.6 to 19.5 A. Time-resolved emission studies indicate the presence of two distinct species, a major long-lived component of -1500 ns ('90%) and a minor shortlived component of -400 ns (

Rapid photoinduced electron transfer was observed with supramolecular assemblies of donor and acceptor metal complexes at the galleries of n-butylammonium salt of α-zirconium phosphate ((C4H9NH3)2Zr(PO4)2·xH2O, abbreviated as BAZrP). Tris(2,2‘-bipyridyl)ruthenium(II)2+ luminescence, for example, was quenched by tris(2,2‘-bipyridyl)cobalt(III)3+ with rate constants exceeding 1.6 × 1012 m2 mol-1 s-1, when the metal complexes were intercalated in the galleries of BAZrP. The quenching rates were unaffected when the viscosity of the BAZrP 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 the donor and the acceptor proceed at essentially the same rate as at room temperature indicating a very low activation energy for the electron transfer reaction. These activation-less rate constants are faster than anticipated for diffusion controlled electron transfer rates at BAZrP galleries, at low temperatures. Excited-state energy migration from donor to donor (antenna effect) followed by electron transfer between the nearest donor−acceptor pairs is one explanation proposed to account for the above observations.

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