Mihaiela C. Stuparu

Facile and General Preparation of Multifunctional Main-Chain Cationic Polymers through Application of Robust, Efficient, and Orthogonal Click Chemistries

Poly(ß-hydroxyl amine)s are prepared from readily available small molecular building blocks at ambient conditions. These macromolecules can be transformed into main-chain cationic polymers upon quaternization of the backbone amine units. The modular and mild nature of the synthesis allows for incorporation of multiple (2-4) chemically distinct reactive sites in the polymer chain. Modifications of the reactive sites afford multifunctional polymers with tunable properties. The orthogonal nature of the involved chemistries sets the synthetic pathway free from any functional group protection/deprotection requirements. This feature also allows for alteration of the modification sequence.

Homopolymer bifunctionalization through sequential thiol–epoxy and esterification reactions: an optimization, quantification, and structural elucidation study

In this study, we probe various aspects of a post-polymerization double-modification strategy involving sequential thiol–epoxy and esterification reactions for the preparation of dual-functional homopolymers. For this, a general reactive scaffold, poly(glycidyl methacrylate), carrying an aromatic end-group was prepared through an atom transfer radical polymerization (ATRP) process. The glycidyl side-chains of this polymer were subjected to a base-catalyzed ring opening reaction with the thiol nucleophiles. A systematic variation in the catalyst type, catalyst loading, reaction medium, reaction temperature, and reaction time suggested that the choice and amount of catalyst had a significant impact on the outcome of the thiol–epoxy reaction. End-group analysis by 1H-NMR spectroscopy was employed to quantify the degree of the epoxy group conversion into the corresponding thio-ether moiety. The secondary hydroxyl groups generated as a result of the first functionalization reaction were then employed in the anchoring of a second functional group to the polymer repeat unit through an esterification reaction. Quantification studies suggested that an excess of the activated acid molecules was necessary to observe quantitative functional group transformation. Elemental analysis confirmed the chemical composition of the functionalized polymers. The obtained bi-functionalized polymers could be converted into a water soluble amphipathic structure in which each polymer repeat unit was substituted with a hydrophilic ammonium cation and a hydrophobic alkyl chain. Besides these, a carefully planned model compound study was also conducted to examine the regio-chemical aspects of the prepared polymers.

Structural, optical, and electrochemical properties of three-dimensional push-pull corannulenes.

Electrochemically active corannulene derivatives with various numbers of electron-donating 4-(N,N-dimethylamino)phenylethynyl (1-4) or electron-withdrawing cyanobutadienyl peripheral substitutents (5-8) were prepared. The latter derivatives resulted from formal [2 + 2] cycloaddition of cyanoolefins to 1-4 followed by retro-electrocyclization. Conformational properties were examined by variable-temperature NMR and X-ray diffraction and opto-electronic properties by electronic absorption/emission spectra and electrochemical measurements; these analyses were corroborated by dispersion-corrected density functional calculations at the level of B97-D/def2-TZVPP. In CH(2)Cl(2), 1-4 exhibit intramolecular charge-transfer (ICT) absorptions at 350-550 nm and green (λ(em) ~ 540 nm) or orange (600 nm) fluorescence with high quantum yields (56-98%) and are more readily reduced than corannulene by up to 490 mV. The variation of optical gap and redox potentials of 1-4 does not correlate with the number of substituents. Cyanobutadienyl corannulenes 5-8 show red-shifted ICT absorptions with end-absorptions approaching 800 nm. Intersubstituent interactions lead to distortions of the corannulene core and lower the molecular symmetry. NMR, X-ray, and computational studies on 5 and 8 with one cyanobutadienyl substituent suggested the formation of intermolecular corannulene dimers. Bowl-inversion barriers around ΔG(‡) = 10-11 kcal/mol were determined for these two molecules.

Phase separation of supramolecular and dynamic block copolymers

The growing synergy between supramolecular chemistry and polymer synthesis is driven by the realization that the dynamic nature of non-covalent interactions may bring new properties and material performance to the field of polymer science. This is manifested in the area of block copolymer self-assembly where supramolecular systems have displayed remarkable morphologies and properties not attained in classic covalent systems. This review article examines the broad strategy of combining phase separation of block copolymers with the dynamic properties of supramolecular interactions.

Rationally Designed Polymer Hosts of Fullerene

A class of its own: A new class of fullerene C60 hosts--polymeric in nature--has been developed by careful design of the molecular structure of the polymer repeat unit and the mode of interaction between the repeat unit and C60 (see picture). As these hosts are synthesized by free-radical polymerization, polymer hosts with various chemical compositions and architectures can be constructed readily by appropriate design of the receptor monomer.

Photon Driven Transformation of Cesium Lead Halide Perovskites from Few-Monolayer Nanoplatelets to Bulk Phase

Influence of light exposure on cesium lead halide nanostructures has been explored. A discovery of photon driven transformation (PDT) in 2D CsPbBr3 nanoplatelets is reported, in which the quantum-confined few-monolayer nanoplatelets will convert to bulk phase under very low irradiation intensity (≈20 mW cm-2 ). Benefiting from the remarkable emission color change during PDT, the multicolor luminescence photopatterns and facile information photo-encoding are established.

π-Conjugated Discrete Oligomers Containing Planar and Nonplanar Aromatic Motifs

A new family of π-conjugated oligomers featuring a nonplanar polycyclic aromatic hydrocarbon, corannulene, and a planar aromatic unit, thiophene, is synthesized through an iterative metal-catalyzed coupling protocol. The two structural motifs are connected through an acetylene linkage. In the shorter oligomers, a thiophene unit is attached to one or two corannulenes. In the higher analogues, two, three, and four thiophene units are placed in an alternating fashion with three, four, and five corannulene units, respectively. Photophysical studies reveal extended π-effects that initially increase and then attenuate as a function of the oligomer length. Notably, longer oligomers are found to be highly active for nonlinear absorption and emission properties. The oligomer with three corannulene and two thiophene units exhibits a two-photon absorption cross section of 600 GM and two-photon-excited intense green luminescence. This work, therefore, introduces the concept of combining planar and nonplanar aromatic motifs in the design of π-conjugated discrete oligomers, establishes synthetic feasibility of such hybrid materials, reports on their photophysical properties that is anticipated to have significant implications for future research targets, and features the discovery that corannulene derivatives can exhibit excellent nonlinear optical activity when extended through π-bridges.

Effect of precursor chemical composition on the formation and stability of G-quadruplex core supramolecular star polymers

A homologous series of guanosine end-functional poly(butadiene)s has been prepared. The potassium cation-templated assembly of these guanosine functionalised precursors then furnished supramolecular star polymers with a G-quadruplex core. Comparison with the previously reported poly(ethylene glycol)-based supramolecular star polymers revealed that in designing supramolecular star polymers, chemically non-polar assembly precursors – that do not interfere with the supramolecular interactions of the core – are essential for the preparation of high stability and high molecular weight supramolecular branched architectures. In addition, in comparison to star polymers composed of chemically polar polymer chains, the non-polar supramolecular ensembles show chain-length independent properties.

Towards Molecular Ribbons of Corannulene

Herein, we explore the synthesis of corannulene-based ribbon-shaped molecules through a repetitive Diels-Alder strategy. For this, appropriate corannulene-based dienes and dienophiles were identified and synthesized. These building blocks could be combined in a modular way to obtain the dimeric and trimeric segments of the hypothetical molecular ribbons. 1D and 2D NMR measurements, along with crystal-structure analyses, allowed the structures and geometries of the synthesized compounds to be determined.

Photoacoustic induced surface acoustic wave sensor for concurrent opto-mechanical microfluidic sensing of dyes and plasmonic nanoparticles

While there are a large number of reports on acoustic wave based sensors for evaluating mechanical parameters of fluid samples such as density, viscosity etc., devices for the simultaneous optical and mechanical characterization of fluids remain unexplored. In this context, effective utilization of surface acoustic wave (SAW) sensors comprising elliptically polarized evanescent waves for optical characterization of an analyte is intriguing. A combination of SAW and photoacoustic (PA) techniques presents promising capabilities for optical and mechanical characterization of fluids in micro volumes. We present a SAW-PA integrated device combining PA and SAW where the samples are introduced into a microfluidic channel. The PA signal generated from a sample in the microchannel of the SAW-PA device is mode-converted into SAW signals upon reaching the piezoelectric substrate, which is detected using the inter-digital transducer (IDT) deposited on the substrate. We further demonstrate the use of this SAW-PA compact platform for investigating the opto-acoustical properties of standard dye solutions and gold nanoparticles whose absorption is due to plasmonic resonance.