Sandwich-type (phthalocyaninato)(porphyrinato) europium triple-decker nanotubes. Effects of the phthalocyanine peripheral substituents on the molecular packing

Abstract

Three sandwich-type (phthalocyaninato)(porphyrinato) europium triple-decker complexes, namely Eu₂(Pc)₂(TClPP) (1), Eu₂[Pc(β-OC₄H₉)₈]₂(TClPP) (2), and Eu₂[Pc(β-OC₈H₁₇)₈]₂(TClPP) (3), have been designed, synthesized, and fabricated into nanotubes using nanoporous anodized aluminium oxide (AAO) membrane as the template. In particular, the effects of peripheral-substituents at the two phthalocyanine ligands in the triple-decker molecule on the molecular stacking relative to the alumina surface and the molecular packing mode in the nanotubes were clarified on the basis of the scanning electron microscopy (SEM), spectroscopic, and X-ray diffraction results. High-resolution TEM (HRTEM) images, in combination with the electronic absorption and XRD results, indicate that the discotic molecules of 1 without peripheral substituent on the phthalocyanine ligands form columnar structures on the alumina surface with homeotropic molecular stacking depending on the intermolecular π–π interactions in a head-to-tail manner. In good contrast, introduction of eight long octyloxy substituents at the peripheral-positions of the phthalocyanine ligands of 3 induces an increase in the interaction of the triple-decker molecules with the alumina surface, resulting in the formation of nanotubes with discotic molecules of 3 parallel stacking relative to the alumina surface depending on the intermolecular π–π interactions in a face-to-face manner. Most interestingly, introduction of eight shorter length butyloxy substituents at the peripheral-positions of the phthalocyanine ligands of 2 leads to the formation of nanotubes with discotic molecules of 2 parallel stacking relative to the alumina surface but depending on the intermolecular π–π interactions in a head-to-tail manner. X-Ray diffraction (XRD) data confirm the above-mentioned results.