Hierarchical self-assembly of an excitation-wavelength-dependent emissive fluorophore and cucurbiturils for secondary encryption

Employing excitation-wavelength-dependent emissive molecules as building blocks for hierarchical self-assembly with ordered multilevel nanostructures as well as various emission colors remains a great challenge for bottom-up materials. Here we report a butyl-modified carbazolyl pyridinium derivative (4,4'-(9H-carbazole-2,7-diyl)bis(1-butylpyridin-1-ium) dibromide [CPDB]) with variable excitation-wavelength-dependent emission colors, including blue, green, yellow, and white light, because of the dynamic protonation on the pyrrole group of the carbazole. CPDB itself assembles as nanoparticles, but it can co-assemble with cucurbit[8]uril (CB[8]) via host-guest complexation to form 1D worm-like nanoribbons, 2D rectangular nanoplates, and 3D microscale polyhedrons at different CPDB/CB[8] molar ratios because of their hierarchical co-assembly modes. By co-assembling with CB[8], CPDB shows another fluorescence variation from blue to orange with obvious emission enhancement. Finally, a secondary encryption system is constructed by CPDB and its supramolecular co-assemblies with cucurbiturils that shows response to excitation wavelength and addition of cucurbiturils.