Directly linked porphyrin arrays with tunable excitonic interactions.

On the basis of the Ag(I)-promoted coupling reaction of Zn(II) 5,15-diaryl porphyrin that gave a meso-meso-linked diporphyrin, we developed a variety of directly linked porphyrin arrays including linear, windmill, gridlike, cyclic, and box architectures. Electronic and excitonic interactions are thus fine tuned by placing porphyrin chromophores in well-defined arrangements. Photoexcited-state dynamics of these porphyrin arrays, as revealed by various ultrafast laser-based measurements, are pertinent to photosynthetic light-harvesting antenna in terms of very efficient excitation energy hopping over many porphyrins and lack of a defect that acts as energy sink. The conformational flexibility of a meso-meso-linked diporphyrin has also been used for the fine tuning of excitonic interactions as demonstrated by strapped meso-meso diporphyrins and reversible switching of energy transfer in a triporphyrin. Triply linked porphyrin arrays have also been explored, which exhibit an exceptionally low HOMO-LUMO gap as a result of a fully conjugated pi electronic system over a coplanar platform.