Metallation of a cyclic chlorophyll hetero-dyad, and the optical properties of synthetic metallo-dyads

A cyclic chlorophyll hetero-dyad 1 -H 2 H 2 , prepared by double ester linking of two structurally different pyropheophorbide- a moieties through 3-CH 2 OCO-13 2 ′ and 17 2 -COOCH 2 -3′, was metallated with zinc and copper to give mono and di-metallated complexes 1 -MH 2 or 1 -H 2 M and 1 -MM. The metallation proceeded stepwise and regioselectively, with predominant synthesis of one of the two mono-metallated complexes 1 -MH 2 as intermediate. The di-zinc complex produced, 1 -ZnZn, was demetallated exclusively via the same mono-zinc complex 1 -ZnH 2 as was the major intermediate during metallation. Visible and/or circular dichroism spectra of 1 -H 2 H 2 , 1 -MH 2 , 1 -H 2 M, and 1 -MM (M = Ni, Cu, or Zn) were measured in organic solvents. Intramolecular interaction of chlorin chromophores is discussed and compared with that of the corresponding monomeric species.