Supramolecular sensitizer–relay assemblies. An evaluation of binding constants from non‐linear stern–volmer plots

A novel technique for determining the binding constants of host–guest complexes, viz. the bis‐cationic electron relays methylviologen and octylviologen in the macrocyclic host of novel (bisheteroleptic) crown ether‐ruthenium sensitizers, is described. This technique allows the separation of the quenching effects of bound and free electron relays. It can be used to calculate binding constants in non‐covalently linked supramolecular systems evaluating the electron transfer process between guest and host. High binding constants comparable to those in many natural enzymes and the photosynthetic reaction centre were found. As an explanation for the behaviour of the sensitizers bound to the bipyridinium cations it is suggested that photoelectron transfer affects the binding between the excited sensitizer and the bound acceptor.