J-dimer emission in interwoven metal-organic frameworks.

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Photophysics

Background:

• J-dimer emission, a phenomenon of paired fluorophores, typically occurs in dilute solutions.
• J-dimer emission has not been previously observed in concentrated or solid-state materials.
• Multivariate (MTV) metal-organic frameworks (MOFs) offer potential for isolating molecular aggregates within crystalline structures.

Purpose of the Study:

• To investigate the possibility of forming J-dimers in the solid state using MTV MOFs.
• To control J-aggregate density during MOF crystallization via a substitutional solid solution approach.
• To thermodynamically quantify link-link interactions during MOF assembly.

Main Methods:

• Synthesis of interwoven PIZOF-2/NNU-28 MTV MOFs with varying amounts of a diethynyl-anthracene aggregate-forming link.
• Controlled crystallization using a substitutional solid solution strategy.
• Photophysical characterization, including fluorescence spectroscopy and lifetime measurements.

Main Results:

• J-dimers were successfully identified across the entire composition range of the PIZOF-2/NNU-28 MOFs.
• Bulk crystals exhibited a systematic red-shift in fluorescence and characteristic π-π stacked aggregate properties.
• Photophysical studies yielded an equilibrium constant for dimerization (K_D = 1.5 ± 0.3 M⁻¹).

Conclusions:

• Supramolecular effects significantly influence the crystallization of MTV MOFs.
• The study demonstrates the successful preparation of solid-state materials with solution-like J-dimer emission.
• This work opens new avenues for designing solid-state materials with tunable optical properties.