Fullerene bridged metallocyclodextrin donor–acceptor complexes: optical spectroscopy and photophysics

Abstract

Two pyridine substituted β-cyclodextrins have been synthesized and coordinated to the photoactive metal centres, [Ru(II)(bpy)₂] and [Re(I)(CO)₃bpy], where bpy is 2,2′-bipyridyl. The photophysical and electrochemical properties of these model complexes have been examined and compared with dinuclear complexes formed when C₆₀ was included between two cyclodextrin cavities of the metallocyclodextrin units. On inclusion of C₆₀, significant quenching of the emission of the luminophores is observed. Concentration and laser power dependence confirm that this quenching is intramolecular. The quenching process is interpreted in terms of a photoinduced electron transfer between the photosensitizer and C₆₀ centre on the basis of spectroscopic and electrochemical evidence. Rate constants of 1.3 ± 0.1 × 10⁸ and 7.0 ± 0.4 × 10⁷ s⁻¹ have been determined for the Ru and Re based complexes, respectively. Significantly, these large rate constants indicate that that there is substantial electronic communication across the cyclodextrin at least for excited state processes.