2 research outputs found
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
Bacterial Cellulose Ionogels as Chemosensory Supports
To
fully leverage the advantages of ionic liquids for many applications,
it is necessary to immobilize or encapsulate the fluids within an
inert, robust, quasi-solid-state format that does not disrupt their
many desirable, inherent features. The formation of ionogels represents
a promising approach; however, many earlier approaches suffer from
solvent/matrix incompatibility, optical opacity, embrittlement, matrix-limited
thermal stability, and/or inadequate ionic liquid loading. We offer
a solution to these limitations by demonstrating a straightforward
and effective strategy toward flexible and durable ionogels comprising
bacterial cellulose supports hosting in excess of 99% ionic liquid
by total weight. Termed bacterial cellulose ionogels (BCIGs), these
gels are prepared using a facile solvent-exchange process equally
amenable to water-miscible and water-immiscible ionic liquids. A suite
of characterization tools were used to study the preliminary (thermo)Âphysical
and structural properties of BCIGs, including no-deuterium nuclear
magnetic resonance, differential scanning calorimetry, thermogravimetric
analysis, scanning electron microscopy, and X-ray diffraction. Our
analyses reveal that the weblike structure and high crystallinity
of the host bacterial cellulose microfibrils are retained within the
BCIG. Notably, not only can BCIGs be tailored in terms of shape, thickness,
and choice of ionic liquid, they can also be designed to host virtually
any desired active, functional species, including fluorescent probes,
nanoparticles (e.g., quantum dots, carbon nanotubes), and gas-capture
reagents. In this paper, we also present results for fluorescent designer
BCIG chemosensor films responsive to ammonia or hydrogen sulfide vapors
on the basis of incorporating selective fluorogenic probes within
the ionogels. Additionally, a thermometric BCIG hosting the excimer-forming
fluorophore 1,3-bisÂ(1-pyrenyl)Âpropane was devised which exhibited
a ratiometric (two-color) fluorescence output that responded precisely
to changes in local temperature. The ionogel approach introduced here
is simple and has broad generality, offering intriguing potential
in (bio)Âanalytical sensing, catalysis, membrane separations, electrochemistry,
energy storage devices, and flexible electronics and displays