Confinement-Driven Aggregate Formation of Photoacids within Porous Metal-Organic Frameworks

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Photophysics

Background:

• Metal-organic frameworks (MOFs) are hybrid materials with tunable structures.
• MOFs can host guest molecules, influencing their photophysical properties.
• Pore confinement in MOFs can affect dye aggregation and emission characteristics.

Purpose of the Study:

• To investigate the emission properties of photoacid dyes within various MOF scaffolds.
• To determine the role of MOF structure versus pore environment on dye aggregation and fluorescence.
• To explore the formation of H- or J-like aggregates of photoacids within MOFs.

Main Methods:

• Incorporation of fluorosolvatochromic methylated photoacid (MePhos) and photoacid (Phos) into different MOF structures.
• Analysis of emission properties, including spectral shifts and aggregation behavior.
• Correlation of observed photophysical changes with MOF structural characteristics.

Main Results:

• MOF confinement induced significant emission red shifts, surpassing those observed in polar solvents.
• Dye aggregation, rather than pore environment modulation of the band gap, was identified as the primary factor influencing emission.
• The MOF structure dictated the type of aggregation, leading to either H- or J-like photophysical characteristics.

Conclusions:

• MOF structure plays a critical role in controlling the aggregation and emission of embedded photoacid dyes.
• The observed phenomena are driven by structural confinement effects leading to aggregation, not solely by pore physicochemical properties.
• This study highlights the potential of MOFs as platforms for tuning photophysical properties through controlled molecular aggregation.