Light Energy Collection in a Porphyrin-Imide-Corrole Ensemble

An assembly consisting of three units, that is, a meso-substituted corrole (), 1,8 naphthaleneimide (), and a Zn porphyrin (), has been synthesized. NIE is connected to C3 through a 1,3-phenylene bridge and to the ZnP unit through a direct CC bond. The convergent synthetic strategy includes the preparation of a trans-A2B-corrole possessing the imide unit, followed by Sonogashira coupling with a meso-substituted A3B-porphyrin. The photophysical processes in the resulting triad are examined and compared with those of the corresponding dyad and the constituent reference models , , and . Excitation of the NIE unit in leads to a fast energy transfer of 98% efficiency to C3 with a rate ken=7.5x1010s1, whereas excitation of the corrole unit leads to a reactivity of the excited state identical to that of the model , with a deactivation rate to the ground state k=2.5x108s1. Energy transfer to C3 and to ZnP moieties follows excitation of NIE in the triad . The rates are ken=7.5x1010s1 and ken=2.5x1010s1 for the sensitization of the C3 and ZnP unit, respectively. The light energy transferred from NIE to Zn porphyrin unit is ultimately funneled to the corrole component, which is the final recipient of the excitation energy absorbed by the different components of the array. The latter process occurs with a rate ken=3.4x109s1 and 89% efficiency. Energy transfer processes take place in all cases by a Forster (dipoledipole) mechanism. The theory predicts quite satisfactorily the rate for the ZnP/C3 couple, where components are separated by about 23 angstrom, but results in calculated rates that are one to two orders of magnitude higher for the couples NIE/ZnP (D/A) and NIE/C3, which are separated by distances of about 14 and 10 angstrom, respectively.