Excimer Formation Dynamics of Dipyrenyldecane in Structurally Different Ionic Liquids.

Area of Science:

• Physical Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Ionic liquids offer tunable properties for molecular aggregation studies.
• Bifluorophoric probes like 1,3-bis(1-pyrenyl)decane [1Py(10)1Py] are sensitive to their environment.
• Understanding solute-environment interactions in ionic liquids is crucial for their application.

Purpose of the Study:

• Investigate intramolecular excimer formation dynamics of [1Py(10)1Py] in various ionic liquids.
• Determine the influence of ionic liquid structure, viscosity, and temperature on excimer formation.
• Explore the relationship between cyclization dynamics and ionic liquid properties.

Main Methods:

• Spectroscopic analysis of [1Py(10)1Py] in seven different ionic liquids across a 10-90 °C temperature range.
• Measurement of excimer-to-monomer emission intensity ratio (I_E/I_M).
• Analysis of excited-state intensity decay kinetics and determination of apparent rate constants (k_a) and activation energies (E_a).

Main Results:

• Excimer formation efficiency (I_E/I_M) increased with temperature in a sigmoidal manner.
• Ionic liquid structure significantly controlled excimer formation, even at similar viscosities.
• Excimer formation rate constants (k_a) were lower in viscous ionic liquids and showed higher temperature sensitivity with increased activation energy (E_a).
• Stokes-Einstein relationship was followed in [Tf₂N^-] based ionic liquids, indicating diffusion-controlled cyclization.

Conclusions:

• The chemical structure of ionic liquids profoundly impacts intramolecular excimer formation dynamics.
• Viscosity and temperature are key factors governing the cyclization process in ionic liquids.
• Ionic liquid properties dictate the applicability of models like the Stokes-Einstein relationship for solute dynamics.