Nina Fu

Solvent- and pH-Induced Self-Assembly of Cationic Meta-Linked Poly(phenylene ethynylene): Effects of Helix Formation on Amplified Fluorescence Quenching and Förster Resonance Energy Transfer

We reported here the synthesis and characterization of a novel water-soluble, meta-linked poly(phenylene ethynylene) (m-PPE-NEt(2)Me(+)) featuring quaternized side groups. We studied the solvent-induced self-assembly of m-PPE-NEt(2)Me(+) in MeOH/H(2)O solvent mixtures by using UV-vis absorption and fluorescence spectroscopies. The results showed that the polymer folded into a helical conformation and that the extent of helical folding increased with the volume % water in the solvent. This cationic polymer also exhibited unique pH-induced helix formation, which was attributed to the partial neutralization of quaternized side groups at high pH and the meta-links in the main chain of the polymer. Studies on the fluorescence quenching of m-PPE-NEt(2)Me(+) by anthraquinone-2,6-disulfonate (AQS) and Fe(CN)(6)(4-), two small-molecule anionic quenchers with different typical structures, revealed more efficient quenching of helical conformation by AQS than by Fe(CN)(6)(4-). We proposed that the two quenchers most likely interacted with the polymer helix in two different modes; that was, AQS featuring large planar aromatic ring could intercalate within adjacent π-stacked phenylene ethynylene units in the polymer helix, whereas Fe(CN)(6)(4-) mainly bound to the periphery of polymer helix through ion-pair formation. Finally, the results of FRET from the helical polymer to the fluorescein (C*)-labeled polyanions, ssDNA-C* (ssDNA: single-stranded DNA) and dsDNA-C* (dsDNA: double-stranded DNA) also suggested two different modes of interactions. As compared with the FRET to dsDNA-C*, the FRET to ssDNA-C* was slightly more efficient, which was believed to arise from the additional binding of ssDNA-C* with the polymer via intercalation of its exposed hydrophobic bases into the π stack of adjacent phenylene ethynylene units in the polymer helix.

Donor–acceptor conjugated polymers based on thieno[3,2-b]indole (TI) and 2,1,3-benzothiadiazole (BT) for high efficiency polymer solar cells

A universal synthetic strategy toward thieno[3,2-b]indole (TI) derivatives was developed. Three conjugated polymers (PTIBT, PTITBT and PTIDTBT) containing N-alkyl-TI as the donor units, 2,1,3-benzodiathiazole (BT) as the acceptor units and thiophene as the spacers were synthesized. The thiophene spacers have a dramatic impact on the physical and electrochemical properties of these copolymers. These polymer donors were used for the fabrication of bulk heterojunction polymer solar cells (PSCs). Preliminarily, power conversion efficiencies (PCEs) based on the device structure of ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al exhibit a large distinction (1.61% for PTIBT, 5.83% for PTITBT and 1.79% for PTIDTBT) at optimal device fabrication conditions. The device based on PTITBT : PC71BM (1 : 3, w/w) shows the best PCE of 5.83% (Voc = 0.69 V, Jsc = 13.92 mA cm−2, FF = 61.8%), which represents one of the best performances among PCDTBT analogues. In addition, the Jsc of 13.92 mA cm−2 is also among the highest Jsc values of all PCDTBT analogues. On the basis of our results, one can conclude that incorporating TI and its derivatives into donor–acceptor conjugated polymers is a feasible and effective way to develop novel donor materials for high efficiency PSC applications.

Thermally Activated Delayed Fluorescence Organic Dots (TADF Odots) for Time‐Resolved and Confocal Fluorescence Imaging in Living Cells and In Vivo

The fluorophores with long‐lived fluorescent emission are highly desirable for time‐resolved fluorescence imaging (TRFI) in monitoring target fluorescence. By embedding the aggregates of a thermally activated delayed fluorescence (TADF) dye, 2,3,5,6‐tetracarbazole‐4‐cyano‐pyridine (CPy), in distearoyl‐sn‐glycero‐3‐phosphoethanolamine‐poly(ethylene glycol) (DSPE‐PEG2000) matrix, CPy‐based organic dots (CPy‐Odots) with a long fluorescence lifetime of 9.3 μs (in water at ambient condition) and high brightness (with an absolute fluorescence quantum efficiency of 38.3%) are fabricated. CPy‐Odots are employed in time‐resolved and confocal fluorescence imaging in living Hela cells and in vivo. The green emission from the CPy‐Odots is readily differentiated from the cellular autofluorescence background because of their stronger emission intensities and longer lifetimes. Unlike other widely studied DSPE‐PEG2000 encapsulated Odots which are always distributed in cytoplasm, CPy‐Odots are located mainly in plasma membrane. In addition, the application of CPy‐Odots as a bright microangiography agent for TRFI in zebrafish is also demonstrated. Much broader application of CPy‐Odots is also prospected after further surface functionalization. Given its simplicity, high fluorescence intensity, and wide availability of TADF materials, the method can be extended to develop more excellent TADF Odots for accomplishing the challenges in future bioimaging applications.

D–A conjugated polymers based on thieno[3,2-b]indole (TI) and 2,1,3-benzodiathiazole (BT) derivatives: synthesis, characterization and side-chain influence on photovoltaic properties

A facile synthetic strategy toward thieno[3,2-b]indole (TI) derivatives was developed by the Cadogan annulation method. Three donor–acceptor (D–A) conjugated polymers P1, P2 and P3 containing N-alkyl-TI derivatives and 4,7-dithien-5-yl-2,1,3-benzodiathiazole (DTBT) derivatives were successfully synthesized and applied to bulk heterojunction (BHJ) polymer solar cells (PSCs). Different side chains were introduced to TI units (for P2) or DTBT units (for P3), the results indicate that the bandgaps, energy levels and photovoltaic performance were finely tuned by the side chains in the TI-DTBT copolymer. Power conversion efficiencies (PCEs) based on the device structure of ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al exhibit a large distinction (1.61% for P1, 0.53% for P2 and 2.73% for P3) under optimal device fabrication conditions. The optimized devices based on P3:PC71BM blends with a relatively higher mobility (2.84 × 10−5 cm2 V−1 s−1) show the best PCE under air mass 1.5 global (AM 1.5 G) irradiation of 100 mW cm−2, which is in good agreement with its high current density and light absorption property. Accordingly, the TI unit can be used as the efficient donor units for D–A conjugated donor materials for PSCs application. In addition, this work suggests that the side chains on low bandgap polymers significantly impact their molecular energy levels and the observed PCEs of the corresponding BHJ solar cells.

Highly Contorted 1,2,5-Thiadiazole-Fused Aromatics for Solution-Processed Field-Effect Transistors: Synthesis and Properties.

A straightforward strategy has been used to construct 1,2,5-thiadiazole-fused 12-ring π systems through twofold Stille coupling and subsequent cyclodehydrogenation by utilizing the building blocks of naphthodithiophene and 5,6-substituted benzo[b]-2,1,3-thiadidazole. Molecules 1 a and 1 b, which exhibit highly contorted π surfaces, show a butterfly-shaped conformation according to DFT calculations. Within the molecules, a plane-to-plane angle of 44.8° was found. UV/Vis absorption, thermogravimetric analysis, differential scanning calorimetry, and cyclic voltammetry (CV) were used to study their physical properties. Strong intermolecular interactions of the nonplanar molecules were also observed by concentration-dependent (1) H NMR spectroscopy measurements and thin-film XRD characterization. The low-lying LUMO and high-lying HOMO levels of the molecules are -3.73 and -5.48 eV, respectively, as estimated from CV measurements; this indicates their potential as semiconducting materials for solution-processed organic field-effect transistors (OFETS). A field-effect hole mobility of up to 0.035 cm(2)  V(-1)  s(-1) , a threshold voltage of 6.98 V, and a current on/off ratio of 8.65×10(5) in air for 1 a have been demonstrated with the top-contact bottom-gate field-effect transistor device structures; this represents an important step toward the solution-processed OFET application of contorted aromatics.

Unprecedented side reactions in Stille coupling: desired ones for Stille polycondensation

Two types of unprecedented side reactions were identified in the Stille coupling reaction, including the direct C-H stannylation of the α-hydrogen of thiophene and the stannylation of arylbromides with trialkylstannane bromide. These results reveal the major source of enhancements for Stille polycondensation efficiency.

Ni0.33Co0.66(OH)F hollow hexagons woven by MWCNTs for high-performance lithium-ion batteries

A template-free two-step strategy is successfully developed for the low-cost one pot production of Ni0.33Co0.66(OH)F hollow hexagons woven by multi-walled carbon nanotubes (MWCNTs). The MWCNTs in situ thread the hollow Ni0.33Co0.66(OH)F hexagons and form an interconnected three-dimensional network. Owing to the integration of MWCNTs and the formation of a fluoride derivative as well as the unique hollow structure of the Ni0.33Co0.66(OH)F hexagon, the composite presents excellent electrochemical properties including high reversible capacity and stable cycle performance. As materials for lithium ion batteries, the Ni0.33Co0.66(OH)F hollow hexagons woven by MWCNTs deliver a high reversible capacity of 1014 mA h g−1 after 100 charge–discharge cycles (current density of 100 mA g−1). At a current density of 1000 mA g−1, a high capacity of 585 mA h g−1 also could be achieved, indicating the potential application of these materials in high-performance electrochemical energy storage.