Excitation-Wavelength-Dependent Fluorescence Behavior of Some Dipolar Molecules in Room-Temperature Ionic Liquids

Abstract

The fluorescence behavior of several dipolar molecules has been studied in three room-temperature ionic liquids, namely, [BMIM][BF4], [EMIM][BF4], and [BMIM][PF6], as a function of the excitation wavelength. Although a large majority of these systems show normal fluorescence behavior with no excitation wavelength dependence, a few systems surprisingly exhibit fairly strong excitation-wavelength-dependent fluorescence behavior in these media. The excitation-wavelength-dependent shift of the fluorescence maximum is measured to be between 10 and 35 nm. The various fluorescence parameters of the systems have been carefully examined to determine the factors that contribute to this kind of behavior, generally not observed in conventional media. It is shown that the existence of a distribution of energetically different molecules in the ground state coupled with a low rate of the excited-state relaxation processes, viz., solvation and energy transfer, are responsible for the excitation-wavelength-dependent fluorescence behavior of some of the systems.

Heterogeneity in a room-temperature ionic liquid: Persistent local environments and the red-edge effect

“…‡ § The most compelling experimental evidence supporting this prediction is given by a striking finding by Samanta and coworkers (23,24). In their study of time-dependent fluorescence of dipolar molecules in imidazolium-based liquids, they observed that ANF exhibits an excitation-wavelength-dependent fluorescence spectrum.…”

“…This phenomenon, which is called the ''red-edge effect'' (REE), is characteristic of low-temperature glasses, polymers, and organized assemblies like micelles. As Samanta and coworkers (23) explain in their paper, this phenomenon is commonly due to heterogeneity in space (i.e., multiple solvation environments). It is surprising that little theoretical or computational work has considered the REE, although this phenomenon was first reported 30 years ago in several different systems (31)(32)(33).…”

“…Experimental evidence both for non-Gaussian dynamics and the existence of locally heterogeneous environments (23,24) in ionic liquids has recently emerged in the literature. From the limited x-ray crystal structure available, we know that different imidazolium-based solvents tend to crystallize into disordered solids (25), and depending on the cooling rate, one observes crystal polymorphism (26).…”

Direct Electrochemistry of Hemoglobin Immobilized on Hydrophilic Ionic Liquid-chitosan-ZrO2 Nanoparticles Composite Film with Carbon Ionic Liquid Electrode as the Platform

“…51,52 Phosphate buffer solutions (PBS, 0.1 mol/L) were used as the supporting electrolyte. pH values of all solutions were adjusted by 0.1 mol/L phosphoric acid solution and 0.1 mol/L sodium hydroxide solution.…”

Bright, stable, and water-soluble CuInS2/ZnS nanocrystals passivated by cetyltrimethylammonium bromide

“…Although many important results have been achieved in the field of bioapplications, basic studies still need to be carried out further, such as effects of the surrounding on the PL of water-soluble quantum dot NCs. In recent years, the previous work presented the effects of pH [6], ligands [7], and excitation wavelength [8] on the optical properties of water-soluble NCs for bioprobes [ 9]. Therefore, a phase transfer from oil to water is imperative to ensure the water solubility of the CIS NCs before further biological applications.…”