Modulating Chirality-Selective Photoluminescence of Single-Walled Carbon Nanotubes by Ionic Liquids

The chirality-selective near-infrared emission of surfactant-stabilized single-wall carbon nanotubes could be controlled by simply varying the anion of the commonly used 1-butyl-3-methylimidazolium ionic liquids. This result advances the notion of the designer solvent ability of ionic liquids and provides opportunities for modulating the properties of nanomaterials.

Aggregation of Carbocyanine Dyes in Choline Chloride-Based Deep Eutectic Solvents in the Presence of an Aqueous Base

Deep eutectic solvents (DESs) have shown potential as novel media to support molecular aggregation. The self-aggregation behavior of two common and popular carbocyanine dyes, 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazole carbocyanine (TDBC) and 5,5'-dichloro-3,3'-di(3-sulfopropyl)-9-methyl-benzothiacarbo cyanine (DMTC), is investigated within DES-based systems under ambient conditions. Although TDBC is known to form J-aggregates in basic aqueous solution, DMTC forms H-aggregates under similar conditions. The DESs used, glyceline and reline, are composed of salt choline chloride and two vastly different H-bond donors, glycerol and urea, respectively, in 1:2 mol ratios. Both DESs in the presence of base are found to support J-aggregates of TDBC. These fluorescent J-aggregates are characterized by small Stokes' shifts and subnanosecond fluorescence lifetimes. Under similar conditions, DMTC forms fluorescent H-aggregates along with J-aggregates within the two DES-based systems. The addition of cationic surfactant cetyltrimethylammonium bromide (CTAB) below its critical micelle concentration (cmc) to a TDBC solution of aqueous base-added glyceline shows the prominent presence of J-aggregates, and increasing the CTAB concentration to above cmc results in the disruption of J-aggregates and the formation of unprecedented H-aggregates. DMTC exclusively forms H-aggregates within a CTAB solution of aqueous base-added glyceline irrespective of the surfactant concentration. Anionic surfactant, sodium dodecylsulfate (SDS), present below its cmc within aqueous base-added DESs supports J-aggregation by TDBC; for similar SDS addition, DMTC forms H-aggregates within the glyceline-based system whereas both H- and J-aggregates exist within the reline-based system. A comparison of the carbocyanine dye behavior in various aqueous base-added DES systems to that in aqueous basic media reveals contrasting aggregation tendencies and/or efficiencies. Surfactants as additives are demonstrated to control and modulate carbocyanine dye self-aggregation within DES-based media. The unique nature of DESs as alternate media toward affecting cyanine dye aggregation is highlighted.

Effect of imidazolium room-temperature ionic liquids on aggregation of amphotericin B: a circular dichroism study

The aggregate–monomer equilibrium of amphotericin B could be controlled by the structure of the room-temperature ionic liquid.

Electrocatalytic reduction of carbon dioxide on a cobalt tetrakis(4-aminophenyl)porphyrin modified electrode in BMImBF4

Electro-catalytic reduction of CO₂ at −0.8 V vs. Ag/AgCl has been studied with poly-Co(ii)-porphyrin on ITO in BMImBF₄ as reaction media.

Spectroscopic and photophysical study of the demetallation of a zinc porphyrin and the aggregation of its free base in a tetraalkylphosphonium ionic liquid

Dissolving zinc tetraphenylporphyrin in the tetraalkylphosphonium chloride ionic liquid P4448Cl results in progressive demetallation of the solute and quantitative production of the free base porphyrin.

Aggregation of a model porphyrin within poly(ethylene glycol) (PEG): effect of water, PEG molecular weight, ionic liquids, salts, and temperature

Porphyrin J-aggregation is facilitated in 10 wt% water-added PEGs at pH 1; it increases with PEG MW and is controlled by RTILs.

The solvation dynamics at millisecond scale of Pd(II)-meso-tetra(4-carboxyphenyl)porphine in solid imidazolium-sulfonate-based ionic liquids

The phosphorescence behavior and solvation dynamics of Pd(II)-meso-tetra(4-carboxyphenyl)porphine (Pd-TCPP) in three imidazolium ionic liquids (ILs) has been studied. The phosphorescence excitation and emission position of Pd-TCPP are dependent on the polarity, constituent ions and structure of the ILs. The phosphorescence decay of Pd-TCPP in these ILs is bi-exponential, and the average lifetimes decrease in the following order: 0.844 ms in 1-butylimidazolium p-toluenesulfonate (HBIMTS)>0.472 ms in 1-butylimidazolium trifluoromethane sulfonate (HBIMTfO)>0.412 ms in 1-butyl-3-methylimidazolium p-toluenesulfonate (BMIMTS). The time-resolved phosphorescence emission spectra (TRPES) of Pd-TCPP display apparently blue-shifts with increasing time. The normalized Stokes shift correlation functions C(t) of Pd-TCPP in these ILs are mono-exponential, and the solvation relaxation times are 2.97, 47.7 and 12.1 ms in HBIMTfO, HBIMTS and BMIMTS, respectively. The solvation dynamics may be attributed to the collective motion of the ion pairs composed of imidazolium cations and counter anions to the area surrounding Pd-TCPP.

The solvation dynamics and rotational relaxation of protonated meso-tetrakis(4-sulfonatophenyl)porphyrin in imidazolium-based ionic liquids measured with a streak camera

For the steady-state behavior of diprotonated tetrakis(4-sulfonatophenyl)porphyrin (H4TPPS2-) in five imidazolium ionic liquids (ILs), the absorption positions of H4TPPS2- primarily depend on the constituent ions of the ILs whereas the emission positions of H4TPPS2- strongly depend on the polarity of the ILs. The fluorescence spectra of H4TPPS2- with different excitation wavelengths show no red-edge effect in our system. The dynamics of H4TPPS2- in ILs is further studied with a streak camera, and the relaxation process of ILs occurs on two different time scales. The short lived component attributed to the local motion of the cations and the anions around the porphine core varies from 32 to 196 ps. The long lived one originated from the collective diffusive motions of the cations and anions varies from 460 to 1072 ps. The average solvation time depends on the viscosity of the ILs. The rotational relaxation times of H4TPPS2- decrease as the viscosity of the ILs decreases.

Circular dichroism studies on intermolecular interactions of amphotericin B in ionic liquid-rich environments

Aggregation of amphotericin B (AmB) in an ionic liquid-rich environment was investigated using circular dichroism (CD) spectroscopy. It was found that nature of the ionic liquids' anion had a strong impact not only on the aggregation of AmB, but more importantly on the nature of AmB aggregates, as observed in the asymmetry of the exciton couplet of the aggregate in CD spectra. Unique CD signals for AmB aggregates were observed in three different 1-butyl-3-methylimidazolium ionic liquid solutions: [C4 -mim]Br favored the formation of AmB aggregates that were similar to those found in water, whereas [C4 -mim]BF4 and [C4 -mim]NO3 produced AmB aggregates that were different from each other and those found in water. The obtained results suggest that the designer solvent ability of ionic liquids could be expanded to address numerous intermolecular processes.

Investigation on the effect of water on the spectroscopic behaviors of TPPS in acidic imidazolium-based ionic liquids

The effect of water on the spectroscopic behaviors of meso-tetrakis-(4-sulfonatophenyl) porphyrin (TPPS) in acidic 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) is investigated by spectroscopic methods. In acidic ionic liquids without water, the Soret bands of the protonated form (H4TPPS2-) and J-aggregates of TPPS are centered at 449 and 469 nm, respectively, and the Q-band is centered at 679 nm. When increasing the content of water, the Soret band of H4TPPS2- is blue-shifted to 430 nm. However, the Soret and Q-bands of J-aggregates are red-shifted to 487 and 701 nm, respectively. The NMR and pyrene-scale polarity experiments reveal that the change of the bulk environment is responsible for the red-shift of J-aggregates and the blue-shift of H4TPPS2-. According to the analysis of the fluorescence spectra, the content of H4TPPS2- increases gradually with the addition of water, while the content of H2TPPS4- takes the opposite trend. Simultaneously, the content of J-aggregates decreases substantially when the addition of water is 0 ~ ca. 12 μL (or 13 μL) but it decreases slowly with further addition of water. Remarkably, the fluorescence intensity of J-aggregates is relatively strong. In addition, the fluorescence of J-aggregates can be detected when λex is set at both λex for TPPS monomers and λex for J-aggregates. While the fluorescence of TPPS monomers can be detected only when λex is set at λex for monomers. Moreover, with the addition of water, the fluorescence lifetimes of H2TPPS4- and H4TPPS2- increase from 3.202 and 0.830 ns to 9.623 and 2.964 ns, respectively.

Effect of ionic liquid on activity, stability, and structure of enzymes: a review

Ionic liquids have shown their potential as a solvent media for many enzymatic reactions as well as protein preservation, because of their unusual characteristics. It is also observed that change in cation or anion alters the physiochemical properties of the ionic liquids, which in turn influence the enzymatic reactions by altering the structure, activity, enatioselectivity, and stability of the enzymes. Thus, it is utmost need of the researchers to have full understanding of these influences created by ionic liquids before choosing or developing an ionic liquid to serve as solvent media for enzymatic reaction or protein preservation. So, in the present review, we try to shed light on effects of ionic liquids chemistry on structure, stability, and activity of enzymes, which will be helpful for the researchers in various biocatalytic applications.

Contrasting behavior of classical salts versus ionic liquids toward aqueous phase J-aggregate dissociation of a cyanine dye

The effect of addition of ionic liquids (ILs) on the aggregation behavior of a cyanine dye, 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazolocarbocyanine (TDBC), was investigated. In basic aqueous buffer solutions (pH ≥ 10), TDBC preferably exists in its J-aggregated form. Addition of hydrophilic ILs > 5 wt % is observed to disrupt the TDBC J-aggregates, converting them to monomer form most likely because of the interaction between bulky IL cation and the J-aggregates in a time-dependent fashion. This is evidenced by the observed increase in monomer band absorbance at the expense of the absorbance band due to J-aggregates over time. Inorganic salts at similar molar concentrations do not cause this phenomenon but instead induce TDBC precipitation. At low concentrations (<5 wt %), the added IL acts similarly to the inorganic salts, reducing the overall absorbance of TDBC in the solution most likely due to cation exchange causing TDBC precipitation. Addition of a molecular solvent, ethanol, at 15 wt % results in an initial increase in monomer absorbance, albeit to a much lesser extent than for the corresponding molar fraction of IL, which then decreases over time with recovery of J-aggregate absorbance--quite opposite the time-dependent behavior seen for TDBC in PB at pH 12.0 with >5 wt % IL. The unique and dual behavior of ILs as an additive toward affecting cyanine dye aggregation is demonstrated.