2 research outputs found
A Synergistic Coassembly of Block Copolymer and Fluorescent Probe in Thin Film for Fine-Tuning the Block Copolymer Morphology and Luminescence Property of the Probe Molecules
Here, we investigate a synergistic coassembly of a block
copolymer,
polystyrene-<i>b</i>-polyÂ(4-vinylpyridine) (PS-<i>b</i>-P4VP), and a fluorescent probe molecule, pyrenebutyric acid (PBA),
in thin film using block copolymer supramolecular assembly (SMA) strategy
for a wide range of compositions tuned by varying the molar ratio
(<i>r</i>) of PBA and 4VP units. The PBA molecules form
supramolecules with PS-<i>b</i>-P4VP through H-bonding between
the carboxylic acid group of 1-pyrenebutyric acid and pyridine ring
of P4VP. For compositions <i>r</i> = 0, 0.1, 0.25, and 0.5,
the SMAs exhibit cylindrical morphology, whereas for <i>r</i> = 0.75 and 1, the SMAs generate lamellar morphology. Interestingly,
it has been observed that the orientation of the microdomains depends
on the solvent used for annealing and can be switched reversibly on
exposing the SMA films to corresponding solvent. In a nonselective
solvent like chloroform, the microdomains are oriented normal to the
substrate, whereas in a selective solvent like 1,4-dioxane, the microdomains
are oriented parallel. The synergistic coassembly of PS-<i>b</i>-P4VP and PBA in SMAs with higher molar ratio results in a structure-within-structure
pattern characterized by two length scales from phase separation of
block copolymer and parallel π–π stacking of the
pyrene moiety of PBA molecules inside the comb block. The photophysical
properties of PBA in different SMAs of varying composition were studied
both in solution and in thin film state and compared to pure PBA.
The UV–vis study shows the H type of aggregation of PBA molecules
inside the comb block by parallel stacking of the pyrene units, and
the PBA molecules orient parallel to the substrate when the microdomains
are oriented normal to the substrate. The pure PBA molecules in thin
film exhibit excimer emission extensively, whereas the PBA molecules
in different supramolecular assemblies exhibit emission ranging from
monomer to mixture of monomer and excimer. The SMA shows more intense
fluorescence emission compared to pure PBA both in solution and in
thin film
UV Cross-Linked Polymer Stabilized Gold Nanoparticles as a Reusable Dip-Catalyst for Aerobic Oxidation of Alcohols and Cross-Aldol Reactions
In this work, a gold nanoparticle (AuNP)-embedded composite
polymer
membrane for dip-catalysis is developed. Primarily, a polyvinylpyrrolidone-stabilized
AuNP (PVP-AuNP) with an average size of 6.50 nm was synthesized by
the reduction of a composite solution of Au salt and PVP. Next, the
composite membrane was fabricated by simply depositing the PVP-AuNP
on the Nylon membrane followed by UV cross-linking. The composite
membrane having the cross-linked PVP-AuNP was utilized as a dip-catalyst
for the aerobic oxidation of alcohols to carbonyl compounds under
oxygen and clean reaction conditions. The catalyst was further tested
for performing cross-aldol reactions. The PVP-AuNP-catalyzed oxidation
reaction also has other noteworthy characteristics, such as a low
catalyst loading (Au, 1.2 mol %), high yield, and selectivity with
a broad substrate scope (aliphatic, aromatic, biphenyl, and heterocyclic
alcohols). The turnover number (TON) and turnover frequency (TOF)
for the oxidation reaction of the alcohol are calculated to be 74.5
and 12.41 h–1, respectively. The P4VP-AuNP dip-catalysts
are highly stable under the reaction conditions without significant
leaching of Au into the solution. The dip-catalyst demonstrates outstanding
reusability up to 10 catalytic cycles while maintaining high catalytic
performance and structural features. It can be easily recovered by
simply pulling it out from the reaction mixture once the reaction
is complete, followed by washing and drying. The practical usefulness
of the suggested method was further demonstrated by the PVP-AuNP-catalyzed
gram-scale synthesis of high-value chemicals like acetophenone. Although
the AuNPs are already used for different reactions, their integration
into dip-catalysts for oxidation of alcohols and cross-aldol reactions
with a wide substrate scope is rare. Overall, these findings demonstrate
that developing composite dip-catalyst systems is a realistic strategy
for creating high-value chemicals in a sustainable and environmentally
friendly way