Photoinduced electron transfer in supramolecular assemblies composed of dialkoxybenzene-tethered ruthenium(II) trisbipyridine and bipyridinium salts

Article abstract of DOI:10.1021/ja00087a026

Ruthenium(II) tris{4,4′-bis[(methyleneoxy)tris(ethyleneoxy)(4-methoxybenzene)]-2, 2′-bipyridine}(1), forms supramolecular complexes with N,N′-dimethyl-4,4′-bipyridinium, MV²⁺ (2), and with cyclo[bis(N,N′-p-xylylene-4,4′-bipyridinium)], BXV⁴⁺ (3). The association constants of the complexes generated between the dialkoxybenzenetethered units of 1 and the electron acceptors 2 and 3 correspond to K_a = 28 ± 1 M^-1 for MV²⁺ and K_a = 1200 ± 100 M^-1 for BXV⁴⁺. Time-resolved laser flash photolysis and steady-state emission studies show that electron transfer from excited 1 proceeds by an intramolecular pathway to the electron acceptors organized in the supramolecular assemblies, k_iq = 1.7 × 10⁸ s^-1 for MV²⁺ and k_iq = 2.9 × 10⁸ s^-1 for BXV⁴⁺, and by a diffusional route from free-uncomplexed 1, k_dq = 1.9 × 10⁸ M^-1 s^-1 for MV²⁺ and k_dq = 3.4 × 10⁸ M^-1 s^-1 for BXV⁴⁺. Formation of the supramolecular 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 β-cyclodextrin.