Design Strategies for Solid-State Supramolecular Arrays Containing Both Mixed-Metalated and Freebase Porphyrins

The design of predictable multichromophoric supramolecular arrays of freebase and metallo porphyrins constitutes an essential first step toward the synthesis of light-harvesting complexes. We now report crystal engineering strategies to achieve the synthesis of controllable and predictable porphyrinic multichromophores in the solid state. The coordination complexes of metal halides, MX2 (M = Cd, Hg, Pb; X = Br, I), with freebase tetrapyridylporphyrin (TPyP) form either 1D, [(HgX2)2TPyP]·2TCE, 1, or 2D, [(MX2)TPyP]·4TCE, (M = Pb, 2; Cd, 3) polymeric networks. The porphyrin cavities in these crystalline networks can be selectively populated with various metal cations to generate ordered multiporphyrinic supramolecular arrays without distorting the coordination networks, either by (a) crystallizing the metal halides and TPyP in the presence of suitable metal salts or by (b) reacting metal halides with a mixture of freebase and metallo porphyrins in specific stoichiometric ratios. A design limit has been reached following approach b, synthesis of the complexes using 100% metalated TPyP results in a change in structure due to intermolecular MTPyP coordination. The UV/vis and fluorescence spectra recorded on partially metalated complexes indicate the presence of the expected absorption and emission bands. Additionally, complex 1 reveals an unusual clathration behavior, wherein the stacking features perpendicular to the porphyrin plane adjust to allow inclusion of variable amounts of identical guest solvent molecules without modification of the layered structure.