Multiconformational Surfaces in Porphyrins:  Previews into Excited-State Landscapes

The crystal structures of four different conformers of the sterically encumbered porphyrins ZnDPP, H2DPP, and NiDPP are reported (DPP = 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin). In combination with two previously published structures of H2DPP and NiDPP, the crystallographic results illustrate the remarkable range of different conformational surfaces possible within a single family of compounds with the same peripheral substituents. These results establish that the multiple conformational landscapes inferred from the excited-state dynamics of the molecules already exist in the ground state and thus offer previews into the conformations that may also be accessible in excited states. Electron paramagnetic resonance (EPR) results for the ZnDPP and NiDPP π cation radicals indicate that the radicals retain a2u spin-density profiles despite the extensive peripheral substitutions and the significant nonplanarity of the parent compounds.