Effect of Ionic Liquids as Cosurfactants on Photoinduced Electron Transfer in Tetronic Micelles

Abstract

This study investigates the role of varying alkyl chain lengths of a series of surface-active 1-alkyl-3-methylimidazolium tetrafluoroborate ([C n MIm]­[BF4], n = 4, 6, and 10) ionic liquids (ILs) as cosurfactants in modifying the micellar characteristics of a tetronic star-block copolymer, T1304, and the consequent effects on bimolecular photoinduced electron transfer (PET) reactions carried out in these T1304–IL mixed micellar systems. Using coumarin 153 as the probe dye and following ground-state absorption, steady-state fluorescence, and time-resolved emission measurements, the micropolarity, microviscosity, and solvent relaxation dynamics in the micellar palisade layer have been revealed both in pure T1304 and in T1304–IL systems. With increasing alkyl chain length of the ILs, the palisade layer of the micelles gradually becomes more polar and less viscous, suggesting better incorporation of the longer alkyl chain length ILs as cosurfactants into the T1304 micelles. The bimolecular PET reactions, involving 7-aminocoumarins as acceptors and N,N-dimethylaniline as the donor, are considerably modulated in T1304 micelles by the presence of the ILs, the effect being more prominent for ILs with longer alkyl chain lengths. In all of the micellar systems, correlations of the electron transfer (ET) kinetics with the reaction exergonicity (−ΔG 0) show clear Marcus inversion (MI) behavior where onsets of MI invariably appear at significantly lower exergonicities, suggesting the involvement of a two-dimensional ET mechanism. Interestingly, the Marcus correlations display significant variations, namely, enhanced reaction rates and gradual shift in the onset of MI toward higher exergonicity, as longer alkyl chain length ILs are sequentially introduced as cosurfactants. From the observed results, it is convincingly realized that 1-alkyl-3-methylimidazolium-based ILs can be used satisfactorily as cosurfactants in tetronic star-block copolymer solutions to modulate PET reactions very significantly for their better utilizations in suitable applied areas.

Fate of Photoinduced Electron Transfer Reactions with Temperature- and pH-Induced Assembly/Disassembly of Star Block Copolymer Micelles

“…Two distinct correlations can be observed at the lower and higher T904 concentration regions, with clear break points that correspond to the CMC (Table S1). The CMC values are found to decrease with either the increase in temperature at a given pH (8.5) or the increase in pH at a given temperature (30 °C) of the medium, in accordance with previous literature reports that high temperature and pH favor the formation of micelles in T904. ,, …”

“…For the present study, five different pH and temperature combinations were considered (pH 8.5, 30 °C; pH 8.5, 50 °C; pH 8.5, 20 °C; pH 10.0, 30 °C; and pH 6.0, 30 °C), to emulate the assembled (micelle) and dissociated (unimer) states of T904. The self-assembly behavior and CMC values under these conditions were monitored by the shift in the emission spectrum of the solvatochromic coumarin dye, C153, with increasing concentrations of the star block copolymer . As depicted in Figure , at pH 8.5, 30 °C; pH 8.5, 50 °C; and pH 10.0, 30 °C, there is initially a sharp decrease in the emission maximum (λ max ) of C153 with progressive addition of T904 to the aqueous solution of the dye, followed by a gradual decrease in λ max at higher concentrations of T904.…”

“…The slower rotational correlation time of the dye in micelles (pH 8.5, 30 °C; pH 8.5, 50 °C, and pH 10.0, 30 °C) compared to the dissociated state of T904 (pH 8.5, 20 °C and pH 6.0, 30 °C) signifies that the dye faces higher rigidity within the confines of the micelle corona. From the average rotational time, the microviscosity (η) of the environment surrounding the dye was determined using the Stokes–Einstein–Debye relation ,, …”

“…The self-assembly and structural versatility of amphiphilic block copolymers are active areas of research with extensive technological applications. − Micelles formed with block copolymers have several advantages over those formed with conventional low-molecular weight surfactants. Some of the favorable attributes of polymeric micelles include lower critical micelle concentration (CMC), greater stability, core–shell structures with enhanced drug loading capacity, and better therapeutic potential and stimulus response. − The poloxamine copolymers (Tetronics) consisting of an ethylene diamine group linked to four arms of repeating ethylene oxide (EO) and propylene oxide (PO) units are especially an interesting class of amphiphiles. − Micelles formed with these star-shaped block copolymers are not only susceptible to temperature changes but also sensitive to pH of the medium. − The central diamine group in Tetronic copolymers allows introduction of positive charges in these nonionic surfactants by protonation. The ensuing Coulombic repulsion between protonated amine groups perturbs the self-assembly of star block copolymers and disrupts micelle formation in acidic pH.…”

Effect of ionic liquids on thermomechanical properties of polyetheretherketone‐multiwalled carbon nanotubes nanocomposites

“…The present study evaluated the mechanical properties of PEEK composites synthesized using ILs, [BMIM] HSO 4 , and [EMIM]Ac (Figure S8) and discovered that [BMIM]HSO 4 -based PEEK composites exhibited better elastic modulus and tensile strength. This explanation was strengthened by earlier research in which several authors 48,49 demonstrated that ILs with a bigger alkyl chain might establish significant interactions with both the filler and polymer matrix, which was critical for improving the MWCNTs distribution and mechanical characteristics.…”