PHOTOINDUCED ELECTRON-TRANSFER IN SUPRAMOLECULAR ASSEMBLIES COMPOSED OF DIALKOXYBENZENE-TETHERED RUTHENIUM(II) TRISBIPYRIDINE AND BIPYRIDINIUM SALTS

Ruthenium(II) hyleneoxy)(4-methoxybenzene)-2,2'-bipyridine}(1), forms supramolecular complexes with N,N'-dimethyl-4,4'-bipyridinium, MV(2+) (2), and with cyclobis(N,N'-p-xylylene-4,4'-bipyridinium), BXV(4+) (3). The association constants of the complexes generated between the dialkoxybenzenetethered units of 1 and the electron accepters 2 and 3 correspond to K-a = 28 +/- 1 M(-1) for MV(2+) and K-a = 1200 +/- 100 M (-1) for BXV(4+), Time-resolved laser flash photolysis and steady-stat e emission studies show that electron transfer from excited 1 proceeds by an intramolecular pathway to the electron accepters organized in t he supramolecular assemblies, k(iq) = 1.7 X 10(8) s(-1) for MV(2+) and k(iq) = 2.9 X 10(8) s(-1) for BXV(4+), and by a diffusional route fro m free-uncomplexed 1, k(dq) = 1.9 X 10(8) M(-1) S-1 for MV(2+) and k(d q) = 3.4 x 10(8) M(-1) s(-1) for BXV(4+). Formation of the supramolecu lar assemblies between 1 and 2 or 3 is supported by the intramolecular electron-transfer quenching of 1 and by the fact that the assemblies dissociate upon addition of beta-cyclodextrin.