Synthesis of [n]Cyclo-5,15-porphyrinylene-4,4′-biphenylenes Displaying Size-Dependent Excitation-Energy Hopping

A set of 5,15‐biphenylene‐bridged porphyrin wheels, namely, [n]cyclo‐5,15‐porphyrinylene‐4,4′‐biphenylenes [n]CPB, have been synthesized through the platination of 5,15‐bis(4‐(pinacolboranyl)phenyl) nickel(II) porphyrin and subsequent reductive elimination of PtII(cod)‐bridged cyclic porphyrin intermediates. The calculated strain energies for [3]CPB, [4]CPB, [5]CPB, and [6]CPB are 49.3, 32.9, 23.5, and 16.0 kcal mol−1, respectively. UV/Vis absorption spectra and cyclic voltammetry indicated characteristic ring‐size‐dependent absorption‐peak shifts and redox‐potential shifts, which presumably reflect the degree of strain in the π‐systems. Excitation‐energy hopping (EEH) times were determined to be 5.1, 8.0, 8.0, and 9.6 ps for [3]CPB, [4]CPB, [5]CPB, and [6]CPB, respectively, in a pump‐power‐dependent TA experiment. Molecular wheels: A series of 5,15‐biphenylene‐bridged cyclic porphyrin arrays (see example; Ar=3,5‐tBu2C6H3) were obtained by the platination of a 5,15‐bis(4‐pinacolateboryl)phenyl NiII porphyrin and subsequent reductive elimination of the PtII(cod)‐bridged cyclic porphyrin intermediates. The 1H NMR and UV/Vis spectra, redox potentials, and intramolecular excitation‐energy‐hopping characteristics of the nanorings depend on the ring size.