This paper describes the thermodynamic characterization of the self-assembly of a Zn trisporphyrin induced by coordination with 1,4-diazabicyclo[2.2.2]octane (DABCO) to form a stable 2:3 double-decker molecular coordination cage that recognizes benzene-1,3,5-tricarboxamides. The self-assembly process has been studied using UV-vis and (1)H NMR spectroscopy and quantitatively characterized in terms of a single stability constant that describes the strength of the individual coordination interactions and two effective molarities (EM) that describe the additional stability imparted by intramolecular cyclization. The EM values of the two consecutive cyclic intramolecular interactions are very similar. At micromolar concentrations, the formation of the fully assembled coordination cage is highly favored over the formation of intermediate species stabilized by fewer interactions, and so self-assembly is an all-or-nothing process. In contrast, at millimolar concentrations, the relative stability of intermediate species increases, leading to a stepwise self-assembly process, and a 2:2 intermediate can be clearly identified using (1)H NMR spectroscopy. The molecular recognition of benzene-1,3,5-tricarboxamides by the cage was investigated using (1)H NMR spectroscopy. The tricarboxamides bind inside the central cavity of the cage complex, and isothermal titration calorimetry (ITC) allowed the quantification of the stoichiometry and binding affinities.

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We describe the construction of self-assembled double-decker porphyrin arrays built up from two covalently connected trimeric Zn-porphyrin units that are joined together by metal-coordination bonds with diamine ligands. We used three different types of diamine ligands: 1,4-diaza[2.2.2]bicyclooctane (DABCO), 4,4'-bipyridine (BIPY), and 5,15-bis(4-pyridyl)-10,20-diphenylporphyrin (DPYP). The ligands act as pillars, through two axial coordination bonds with the porphyrinic Zn(II) ions, to block the planes of the porphyrin units in an almost cofacial orientation and inducing the formation of a trigonal prismatic structure. The spectroscopic and photophysical properties of the Zn-trisporphyrin component were determined as well as those of the resulting multimolecular cagelike assemblies. The double-decker assembly with DPYP as the pillars constitutes a nonameric porphyrin aggregate. Although this assembly is thermodynamically less stable than those containing DABCO or BIPY, efficient photoinduced energy transfer occurs (96% yield) from the trisporphyrin base units to the DPYP side walls. The rate of the energy-transfer process is in good agreement with that calculated for a dipole-dipole (Förster) mechanism corrected for the unfavorable orientation geometry of the donor and the axially bound acceptor.