Synthesis, spectroscopy, electrochemistry, and photophysics of highly conjugated, ethynyl-bridged porphyrin systems

A variety of high yield, versatile synthetic approaches to unusually elaborated porphyrin systems through application of metal-mediated cross-coupling methodologies on a variety of halogenated porphyrinic synthons was developed in our group. Further utilization of this facile synthetic methodology on ethyne-elaborated porphyrin building blocks enabled us to fabricate a new class of porphyrin arrays which are wired together via single ethynyl or oligo-ethynyl linkages. This type of topological connectivity affords exceptional electronic interactions between the chromophores which are manifest in their room temperature photophysics, optical spectroscopy, and electrochemistry. The photophysical properties of these highly conjugated porphyrin arrays can be systematically regulated by modulating the extent of the steric interactions that define the barrier to rotation about the conjugated bridge between the porphyrin chromophores as well as the magnitude of ground state porphyrin-to-porphyrin electronic communication within the supermolecules. A series of porphyrin arrays in which (5, 10, 15, 20-tetraphenylporphinato)zinc(II) and (10, 20-diphenylporphinato)zinc(II) complexes are linked by ethyne or butadiyne groups. The magnitude of electronic and excitonic coupling in these systems depends intimately upon the linkage topology, (meso-to-meso, meso-to-$\beta$, or $\beta$-to-$\beta$). The strong inter-chromophoric exciton coupling in the meso-to-meso porphyrin arrays is manifest in the fact that these species possess a number of unprecedented photophysical properties: for example, fluorescence anisotroscopy measurements demonstrate that these arrays exhibit highly polarized, delocalized, excited states with exceptionally long dephasing times, and highlight the potential of these systems for the engineering of long-range ultrafast, directional, excitation transfer within artificial supramolecular assemblies