Synthesis of Zn-, Mn-, and Fe-containing mono- and heterometallated ethanediyl-bridged porphyrin dimers

New ethanediyl-bridged unsymmetrical mono- and heterometallated dimers of 2 ,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin (H(2)oep) containing transit ion-metal ions (Mn and Fe) were synthesized by a facile stepwise metallatio n/demetallation process under mild conditions. The novel metallation strate gy initially involved the predominant insertion of Zn into one of the two p orphyrin rings of the free-base dimer, followed by the incorporation of Mn or Fe into the other porphyrin ring under exceptionally mild conditions, gi ving corresponding heterometallic dimers; the subsequent removal of Zn yiel ded mono-transition-metal dimers. The emission spectrum of the monozinc dim er predominantly exhibited fluorescence bands of the free-base porphyrin co mponent, indicating a very efficient energy-transfer process. Conversely, e mission of the free-base or Zn porphyrin component of transition metal cont aining dimers was strongly quenched due to photoinduced electron transfer.