Electronically tunable anion-π interactions in pyrylium complexes: experimental and theoretical studies

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Previous studies on anion-π interactions focused on non-heteroaromatic or nitrogen-based systems.
• Organic oxygenated aromatic systems were unexplored for anion-π interactions.

Purpose of the Study:

• To experimentally detect and demonstrate noncovalent anion-π interactions in tri-aryl-pyrylium tetrafluoroborate systems.
• To synthesize and characterize novel pyrylium tetrafluoroborate salts.
• To explore the potential of these compounds as tunable fluorescent dyes.

Main Methods:

• Synthesis of a series of pyrylium tetrafluoroborate salts.
• (19)F NMR spectroscopy to detect and quantify anion-π interactions in solution.
• Density Functional Theory (DFT) calculations to elucidate interaction mechanisms.

Main Results:

• Experimental evidence of noncovalent anion-π interactions between pyrylium cations and tetrafluoroborate anions.
• Correlations between (19)F NMR chemical shifts and pyrylium cation properties confirmed the interaction.
• DFT calculations revealed additional (C-H)(+)-anion hydrogen bonding.
• Tunable fluorescence emission was observed in synthesized compounds.

Conclusions:

• Tri-aryl-pyrylium tetrafluoroborate systems exhibit significant noncovalent anion-π interactions.
• These compounds represent a novel class of tunable fluorescent dyes with potential laser applications.
• The findings expand the scope of known anion-π interacting systems.