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 multi-level 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 exci-tation-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.

Automated summary

Building hierarchical nanostructures with ordered multi-level structures and various emission colors using bottom-up approach is still a challenge. This study presents a molecule with variable emission colors and demonstrates the construction of different nanostructures by co-assembling with other molecules.