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

Four ZnII 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.