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Ionic liquid-controlled J- versus H-aggregation of cyanine dyes
Vinod Kumar1, Gary A Baker, Siddharth Pandey
1Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India.
Chemical Communications (Cambridge, England)
|March 18, 2011
Summary
Cyanine dyes form H-aggregates in [BF(4)]-based ionic liquids, but J-aggregates in others when NaOH is added. This difference is attributed to the distinct hydrolytic properties of [BF(4)]- ionic liquids.
Area of Science:
- Supramolecular Chemistry
- Materials Science
- Physical Chemistry
Background:
- Cyanine dyes are widely used as fluorescent probes and in various optical applications.
- The formation of dye aggregates, such as H-aggregates and J-aggregates, significantly alters their photophysical properties.
- Ionic liquids (ILs) offer unique solvent properties that can influence molecular self-assembly.
Purpose of the Study:
- To investigate the aggregation behavior of cyanine dyes in different ionic liquids upon addition of aqueous NaOH.
- To elucidate the role of the ionic liquid anion in directing the type of dye aggregate formed.
- To explore the potential of ionic liquids for controlling supramolecular dye assembly.
Main Methods:
- Spectroscopic analysis (UV-Vis absorption and fluorescence) of cyanine dye solutions in various ionic liquids.
- Controlled addition of aqueous sodium hydroxide (NaOH) to induce dye aggregation.
- Comparison of aggregation patterns in ionic liquids with tetrafluoroborate ([BF(4)]-) anion versus other anions.
Main Results:
- Fluorescent H-aggregates of cyanine dyes were observed in the ionic liquid [C(n)mim][BF(4)].
- J-aggregates of cyanine dyes formed in ionic liquids containing anions other than [BF(4)]- upon addition of NaOH.
- The observed differences in aggregation are linked to the specific properties of the [BF(4)]- anion.
Conclusions:
- The anion of the ionic liquid plays a critical role in determining the type of cyanine dye aggregate formed.
- Ionic liquids with [BF(4)]- anions exhibit different hydrolytic properties compared to those with other anions, influencing dye aggregation.
- This study highlights the potential for using ionic liquids as tunable media for controlling supramolecular structures of dyes.
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