Photophysical properties of a new, stable corrole-porphyrin dyad

The synthesis of a new stable corrole-porphyrin dyad, made up of a free-base corrole and a free-base porphyrin connected by an amide linker is presented and the characterization of the photoinduced processes taking place in the array is described. The dyad was synthesized from meso-substituted trans-A2B-corrole bearing acid chloride functionality and meso-substituted A3B-porphyrin possessing one free NH2 group. The structure of the dyad was carefully designed and optimized to ensure stability of the molecule. The preparation of the amine component was achieved via phthalimide protection strategy which occurred to be more efficient than the traditional nitro group reduction. Results obtained from time resolved and steady state spectroscopy experiments indicate the existence of an equilibrium between the two lowest singlet excited states of the dyad, one localized on the corrole and the other on the porphyrin unit, which are nearly iso-energetic (ΔG = −0.01 eV). Independently of the excited component, energy transfer occurs in both directions (very likely with a Förster mechanism) and an equilibrium with Keq close to 1 is rapidly set with back and forward rates of the order of 109 s−1. Both states decay with a common lifetime (6.2 ns) that is longer compared to the corrole model (3.9 ns) and shorter with respect to the porphyrin reference (9.9 ns). The longer lived excited state localized on porphyrin acts as a reservoir for the excited state localized on corrole. At 77 K the equilibration does not take place during the lifetime of the excited states, and the decay of the two species occurs independently.