Self-assembly of double-decker cages induced by coordination of perylene bisimide with a trimeric Zn porphyrin: study of the electron transfer dynamics between the two photoactive components

We describe the thermodynamic characterization of the assembly process of a covalently connected trimeric Zn porphyrin 1 induced by coordination to a bispyridyl functionalized perylene bisimide 2. The perylene bisimide ligands act as pillars via two axial coordination bonds with the porphyrinic Zn(II) ions. xing the planes of the porphyrin units in a nearly co-facial orientation and inducing the formation of trigonal prism-like structures. The fully assembled 1(2)center dot 2(3) aggregate and the partially assembled one, 1(2)center dot 2(2), in which only two zinc porphyrin sites of trimeric 1 are axially coordinated to 2, are present in solution in equilibrium with freely diffusing species 1 and 2. The strong quenching observed in the mixture for the luminescence of the components 2 and 1 is ascribed to an efficient photoinduced electron transfer from the Zn porphyrin units of 1 to coordinated 2 occurring upon excitation of both components within the assemblies. In the formed assemblies, the Zn porphyrin units of the trimer 1 behave independently. Thus, the porphyrin units that are not coordinated with 2 in the partially assembled complex, 1(2)center dot 2(2), display the same photophysical behaviour registered for freely diffusing 1. The rate of charge separation within the cage is nearly independent on the polarity of the solvent (ca. 10(10) s(-1)) whereas the charge recombination process, leading to the ground state, has a lifetime of 110 ps in dichloromethane and ca. 6 ns in toluene, in agreement with a Marcus inverted behaviour.