Supramolecular Bis(rutheniumphthalocyanine)−Perylenediimide Ensembles:  Simple Complexation as a Powerful Tool toward Long-Lived Radical Ion Pair States

A novel supramolecular electron donor-acceptor hybrid (1) has been designed through axial coordination of a perylenebisimide moiety BPyPDI, bearing two 4-pyridyl substituents at the imido positions, to the ruthenium(II) metal centers of two phthalocyanines Ru(CO)Pc. This modular protocol enables access to electron donor-acceptor hybrids with potentially great design flexibility. The new array (1) has been characterized by standard spectroscopic methods, and its photophysical behavior has been established by using ultrafast and fast time-resolved techniques. Photoexcitation of either chromophore leads to a product that is essentially identical for both pathways, that is, evolving from the Ru(CO)Pc or BPyPDI singlet excited state. Features of the photoproduct are new transient maxima at 530 and 725 nm, plus transient minima at 580 nm and 650 nm. Based on the radiolytically generated BPyPDI*- (i.e., one-electron reduction of BPyPDI) and Ru(CO)Pc*+ (i.e., one-electron oxidation of Ru(CO)Pc) features, which in the 300 and 900 nm range remarkably resemble those noted for photoexcited 1, we attribute the photolytically generated species to the composite spectrum of the Ru(CO)Pc*+ -BPyPDI*- -RuCOPc radical ion pair state. Its lifetime, which is on the order of 115 +/- 5 ns, reveals a significant stabilization and confirms that the strongly exothermic charge recombination dynamics are placed deeply in the inverted region of the Marcus parabola.