Phenothiazine-Bridged Cyclic Porphyrin Dimers as High-Affinity Hosts for Fullerenes and Linear Array of C_(60) in Self-Assembled Porphyrin Nanotube

摘要

Free-bases and a nickel(II) complex of phenothiazine-bridged cyclic porphyrin dimers bearing self-assembling 4-pyridyl groups (M_2-Ptz-CPD_(Py)(OC_n); M = H_2 or Ni, OC_n = OC_6 or OC_3) at opposite meso-positions have been prepared as host molecules for fullerenes. The free-base dimer (H4-Ptz-CPD_(Py)(OC_6)) includes fullerenes with remarkably high association constants such as 3.9 ± 0.7 × 10~6 M~(-1) for C_(60) and 7.4 ± 0.8 × 10~7 M~(-1) for C_(70) in toluene. This C_(60) affinity is the highest value ever among reported receptors composed of free-base porphyrins. The nickel dimer (Ni_2-Ptz-CPD_(Py)(OC_6)) also shows high affinities for C_(60) (1.3 ± 0.2 × 10~6 M~(-1)) and C_(70) (over 10~7 M~(-1)). In the crystal structure of the inclusion complex of C_(60) within H_4-Ptz-CPD_(py)(OC_3), the C_(60) molecule is located just above the centers of the porphyrins. The two porphyrin planes are almost parallel to each other and the center-to-center distance (12.454 ?) is close to the optimal separation (～12.5 ?) for C_(60) inclusion. The cyclic porphyrin dimer forms a nanotube through its self-assembly induced by C-H···N hydrogen bonds between porphyrin β-CH groups and pyridyl nitrogens as well as π-π interactions of the pyridyl groups. The C_(60) molecules are linearly arranged in the inner channel of this nanotube.