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 ([Eu24L36]n, where L is a fluoroalkyl-rich bis(β-diketonate) ligand). [Eu24L36]n was fabricated by length-restricted heterochiral columnar crystallization of P- and M-Eu6L9 unit tubes to form Eu24L36 nanotubes. X-ray diffraction analysis of [Eu24L36]n revealed that Eu24L36 nanotubes were one-dimensionally aligned and spatially isolated in the crystal lattice, thereby forming monodisperse Eu24L36 channels. [Eu24L36]n absorbed pyrrole (Py) monomers upon soaking in Py liquid through a crystal-to-crystal process ([Eu24L36]n + mPy → [mPy⊂Eu24L36]n), which was directly observed by X-ray diffraction. Photoirradiation of [mPy⊂Eu24L36]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 Eu3+ cores. Thus, the confined photo-oxidative oligomerization process ([mPy⊂Eu24L36]n + hν → [(Py)m⊂Eu24L36]n) can be observed directly by X-ray diffraction, which indicated the formation of ∼(Py)24 inside the monodisperse Eu24L36 nanochannels. Likewise, monodisperse photo-oxidative oligomerization of Py to give octa- and nonapyrrole was achieved using the Eu6L9 unit tube as a template. [Eu24L36]n also absorbed ferrocene (Fc) through a crystal-to-crystal process ([Eu24L36]n + mFc → [mFc⊂Eu24L36]n), where the crystalline-state photoinduced electron transfer from the incorporated Fc to the Eu3+ cores can be monitored by quenching of the Eu3+-red luminescence.