A Single Crystal of Uniform Photoredox-Active Nanochannels for Monodisperse Photo-Oxidative Oligomerization

A single crystal of aligned identical nanotubes with uniform channel lengths and diameters might serve as a porous crystal template with a monodisperse channel structure. However, the polydisperse nature of nanotubes reported to date makes them difficult to fabricate a porous single crystal with monodisperse channels. This work reported the fabrication of a porous single crystal comprising uniform photoredox-active nanotubes ([Eu 24 L 36 ] n, where L is a fluoroalkyl-rich bis(β-diketonate) ligand). [Eu 24 L 36 ] n was fabricated by length-restricted heterochiral columnar crystallization of P - and M -Eu 6 L 9 unit tubes to form Eu 24 L 36 nanotubes. X-ray diffraction analysis of [Eu 24 L 36 ] n revealed that Eu 24 L 36 nanotubes were one-dimensionally aligned and spatially isolated in the crystal lattice, thereby forming monodisperse Eu 24 L 36 channels. [Eu 24 L 36 ] n absorbed pyrrole (Py) monomers upon soaking in Py liquid through a crystal-to-crystal process ([Eu 24 L 36 ] n + m Py → [ m Py⊂Eu 24 L 36 ] n ), which was directly observed by X-ray diffraction. Photoirradiation of [ m Py⊂Eu 24 L 36 ] n drove photo-oxidative oligomerization of the confined Py, during which the nanotube crystal template preserved its crystallinity because of the soft photo-oxidation with the Eu 3+ cores. Thus, the confined photo-oxidative oligomerization process ([ m Py⊂Eu 24 L 36 ] n + h ν → [(Py) m ⊂Eu 24 L 36 ] n ) can be observed directly by X-ray diffraction, which indicated the formation of ∼(Py) 24 inside the monodisperse Eu 24 L 36 nanochannels. Likewise, monodisperse photo-oxidative oligomerization of Py to give octa- and nonapyrrole was achieved using the Eu 6 L 9 unit tube as a template. [Eu 24 L 36 ] n also absorbed ferrocene (Fc) through a crystal-to-crystal process ([Eu 24 L 36 ] n + m Fc → [ m Fc⊂Eu 24 L 36 ] n ), where the crystalline-state photoinduced electron transfer from the incorporated Fc to the Eu 3+ cores can be monitored by quenching of the Eu 3+ -red luminescence.