Influence of Cations on the Fluorescence Quenching of an Ionic, Sterically Congested Pyrenyl Moiety by Iodide in Water

Abstract

Quenching of the excited singlet states of a water-soluble, sterically congested tetraarylpyrene, 1,3,6,8-tetrakis(2,6-dimethyl-4-(α-carboxy)methoxyphenyl)pyrene (Py4C), by a series of iodide salts has been investigated by steady-state and time-resolved fluorescence measurements. Access to the pyrenyl group of Py4C is restricted sterically as a result of the four flanking (2,6-dimethylphenoxy)acetic acid groups and the energy costs associated with their rotation. Deprotonation of the carboxylic acid groups of Py4C permits examination of ion-ion electrostatic interactions on the rates of quenching by iodide salts in which different steric and electrostatic factors are introduced by varying the cationic portions. At the same concentrations and with the same cations, chloride anions are ineffective quenchers. The quenching rate constants of Py4C by iodide are found to correlate linearly with the ionic radii of the cations and their enthalpies of hydration. These correlations are discussed in terms of the Hofmeister series. Furthermore, the results indicate that the cations that flank Py4C decrease the quenching efficiency of iodide through polarization and shielding effects (i.e., lowering the effective charge), which isolate to varying degrees the π-system. The effects of the different cations on quenching the fluorescence of a simpler and sterically unencumbered pyrenyl derivative, 1-pyrenylbutyric acid (PyBu), by iodide are much smaller. Overall, the results with Py4C indicate that the fluorescence quenching efficiency by iodide is influenced by direct interactions with the cations associated with the carboxylate groups of Py4C and not the solvation of water molecules. This observation is germane to a topic of current debate: Are the effects of the cations more closely related to bulk water properties or to direct ion-ion interactions? The conclusions obtained from these studies are applicable clearly to a wide variety of other systems in which ion pairing influences cooperative or inhibitory interactions.

In Situ Monitoring of RAFT Polymerization by Tetraphenylethylene‐Containing Agents with Aggregation‐Induced Emission Characteristics

“…The TPE‐based RAFT agents were non‐emissive both in solution or solid state owing to the quenching effect of the carbonyl sulfur group . However, the polymers derived from them exhibited strong photoluminescence (PL) with AIE characteristics (Supporting Information, Figure S17).…”

“…TheT PE-based RAFT agents were non-emissive both in solution or solid state owing to the quenching effect of the carbonyl sulfur group. [24] However,the polymers derived from them exhibited strong photoluminescence (PL) with AIE characteristics (Supporting Information, Figure S17). Although the polymers contained the same TPE fluorophore, their emission intensity and wavelength differed due to the variation of the Zg roup (Supporting Information, Figure S18).…”

Aggregation‐Induced Emission Boosting the Study of Polymer Science

“…These TPE-based RAFT initiators were nonemissive both in solution or solid state owing to photoinduced electron transfer (PET) effect caused by the carbonyl sulfur groups (Figure 3A). [46,47] The polymers derived from these non-AIE initiators could emit strong light with AIE characteristics. Taking the RAFT polymerization of methyl methacrylate in toluene as example, when the monomer conversion was lower than 34%, the system was hardly emissive in the low viscous medium.…”

In Situ Monitoring of RAFT Polymerization by Tetraphenylethylene‐Containing Agents with Aggregation‐Induced Emission Characteristics

“…[24] However,the polymers derived from them exhibited strong photoluminescence (PL) with AIE characteristics (Supporting Information, Figure S17). [24] However,the polymers derived from them exhibited strong photoluminescence (PL) with AIE characteristics (Supporting Information, Figure S17).…”