β,meso‐Acetylenyl‐Bridged, Asymmetrical, Porphyrin Dyads – Synthesis, Spectral, Electrochemical and Computational Studies

Abstract

AbstractThe first examples of β,meso‐acetylenyl‐bridged, asymmetrical, covalently linked, porphyrin dyads, containing two different subunits, such as ZnN4P‐N3OP (1), ZnN4P‐N3SP (2), ZnN4P‐N2SOP (4) and ZnN4P‐N2S2P (6), were synthesized by the coupling of a β‐acetylenyl, ZnN4 porphyrin with a meso‐bromoheteroporphyrin under mild, Pd0‐catalyzed, coupling conditions. The dyads containing different types of metal‐free subunits, such as N4P‐N3SP (3), N4P‐N2SOP (5) and N4P‐N2S2P (7), were synthesized by the demetallation of the corresponding dyads. The seven β,meso‐acetylenyl dyads 1–7 were characterized by NMR, MS, absorption, fluorescence and electrochemical techniques. The NMR, absorption and electrochemical studies support an electronic interaction between the subunits in all seven dyads. The steady‐statefluorescence studies on dyads 1–7 support an efficient energy transfer from the donor (ZnN4 or N4) subunit to the acceptor heteroporphyrin subunit upon excitation of the ZnN4/N4 subunit. First‐principle‐based, quantum‐chemical studies carried out on dyads 1, 2, 4 and 6 further support an electronic interaction between the donor and acceptor subunits. The computational studies also predict significant tuning of the electronic energy levels in these dyads with the modification of the porphyrin core of the acceptor groups. The calculations support the experimental results of efficient donor→acceptor energy transfer in these dyads.