Synthetic, Structural, and Spectroscopic Studies of Bis(porphyrinzinc) Complexes Linked by Two-Atom Conjugating Bridges

Four Zn^II 5,10,15-triphenylporphyrin (TriPP) complexes meso-meso linked by two-atom bridges, namely, C₂H₂ (2), C₂ (3), CH=N (4), and N₂ (5), were prepared, for comparison of ground-state inter-porphyrin conjugation. The X-ray crystal structure of azoporphyrin 5·py₂ (py = pyridine) was determined: it exhibits a stepped-offset shape and a porphyrin-azo torsion angle of 34.8. Some new monoporphyrin starting materials were prepared, and ZnTriPPNH₂ (27), ZnTriPPCHO (23), NiTriPPCHO (7), and ZnTriPPCH₂CH₂Ph (18), as well as the byproduct butadiyne-linked dimer 26 were characterized by single-crystal X-ray crystallography. The conjugation in the dimers was assessed by electronic absorption and steady-state fluorescence spectroscopy. All show variously split B bands: azoporphyrin 5 clearly has the strongest ground-state inter-porphyrin interactions. Imine 4 and azo 5 show strongly quenched fluorescence emission, which indicates the presence of efficient relaxation pathways afforded by the N-containing linkers.