A fluorescent and phosphorescent nanoporous solid: crystalline calix[4]arene.

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Nanotechnology

Background:

• Calix[4]arene derivatives are known for their ability to form self-assembled structures.
• Nanoporous materials are crucial for applications in separation, catalysis, and sensing.
• Luminescence properties of organic molecules are highly sensitive to their aggregation state and environment.

Purpose of the Study:

• To synthesize and characterize novel nanoporous microcrystals of Calix[4]arene.
• To investigate the structural organization and pore characteristics of these microcrystals.
• To explore the luminescence behavior (fluorescence and phosphorescence) of the material at room temperature.

Main Methods:

• Single-crystal X-ray diffraction to determine crystal structure and pore dimensions.
• Scanning Electron Microscopy (SEM) for morphological analysis.
• Time-resolved photoluminescence spectroscopy to study fluorescence and phosphorescence lifetimes.

Main Results:

• Formation of elongated microcrystals with linear nano-channels (1.7 nm diameter) in a honeycomb arrangement.
• Observation of room-temperature luminescence including monomer fluorescence (τ ≈ 1.1 ns), dimer fluorescence (τ ≈ 5.4 ns), and monomer phosphorescence (τ ≈ 2 s).
• Evidence of dimer formation due to π-orbital overlap between adjacent phenol groups from neighboring nano-channels (C-C distance ≈ 4 Å).

Conclusions:

• Calix[4]arene can self-assemble into ordered nanoporous structures with potential for host-guest chemistry.
• The observed luminescence properties are linked to the specific arrangement of molecules within the nano-channels.
• The material's luminescence characteristics suggest potential applications in optical sensing or light-emitting devices.