Enhanced Photocatalytic Oxygen Evolution Using Copper-Coordinated Perylene Diimide Nanorod Assemblies.

A crystalline supramolecular photocatalyst is prepared through metal-induced self-assembly of perylene diimide with imidazole groups at the imide position (PDI-Hm). Exploiting the metal-coordination ability of imidazole, a crystalline assembly of copper-coordinated PDI-Hm (CuPDI-Hm) in a nanorod shape is prepared which displays an outstanding photocatalytic oxygen evolution rate of 25,900 µmol g-1 h-1 without additional co-catalysts. The imidazole-copper coordination, along with π-π stacking of PDI frameworks, guides the arrangement of PDI-Hm molecules to form highly crystalline assemblies. The coordination of copper also modulates the size of the CuPDI-Hm supramolecular assembly by regulating the nucleation and growth processes. Furthermore, the imidazole-copper coordination constructs the electric field within the PDI-Hm assembly, hindering the recombination of photo-induced charges to enhance the photoelectric/photocatalytic activity when compared to Cu-free PDI-Hm assemblies. Small CuPDI-Hm assembly exhibits higher photocatalytic activity due to their larger surface area and reduced light scattering. Together, the Cu-imidazole coordination presents a facile way for fabricating size-controlled crystalline PDI assemblies with built-in electric field enhancing photoelectric and photocatalytic activities substantially.

A hydrazide organogelator for fluoride sensing with hyperchromicity and gel-to-sol transition.

Sensing of fluoride in a solvent is highly required in healthcare and environmental rehabilitation. Among the various sensing methods, optical sensing has attracted significant research interest because it can conveniently recognize fluoride. Herein, a low molecular weight organogelator, N'1,N'6-bis(3-(1-pyrrolyl)propanoyl) hexanedihydrazide (DPH), containing a central butyl chain conjugated to two pyrrole rings through hydrazide groups, was used for optical sensing of fluoride in the forms of both solution and organogel. Association of fluoride with the -NH moiety of the hydrazide group endowed the DPH solution in dimethylformamide with a hyperchromicity under 350 nm. Exploiting the UV absorptivity, the DPH solution was examined as a chemosensor, displaying good selectivity toward fluoride among various anions and moderate sensitivity with a detection limit of 0.49 µM. The practical use of the DPH solution was demonstrated for fluoride sensing in toothpaste. Binding of fluoride also changed the molecular interactions of the DPH organogel, resulting in a phase transition from gel to sol. This gel-to-sol transition enabled the sensing of fluoride by the naked eye.