Cyclic 2, 12-Porphyrinylene Nanorings as a Porphyrin Analogue of Cycloparaphenylenes

摘要

β-to-β Directly linked cyclic Ni(Ⅱ) porphyrin trimer, tetramer, and pentamer ([3]CP, [4]CP, and [5]CP) have been synthesized by reaction of a 2,12-diborylated Ni(Ⅱ) porphyrin with Pt(cod)Cl_2 followed by reductive elimination. The structures of these cyclic porphyrin arrays have been revealed by X-ray diffraction analysis. The strain energies of these cyclic oligomers are calculated to be 77, 57, and 47 kcal/mol for [3]CP, [4]CP, and [5]CP, respectively. Intramolecular excitation energy hopping was observed between the ~3(d,d) states of the Ni(Ⅱ) porphyrins with rates of 3.0, 4.4, and 4.6 ps for [3]CP, [4]CP, and [S]CP, respectively, reflecting the close proximity of the Ni(Ⅱ) centers.