A Crystalline 2,3-<i>exo</i>-Disyndiotactic Dicyclopentadiene Tetramer

Cycloolefin oligomers and polymers have attracted attention for functional materials, but they are rarely seen in the crystalline state. A new crystalline cycloolefin dicyclopentadiene tetramer, having a 2,3-<i>exo</i>-disyndiotactic structure, is presented. By combining global optimization techniques based on configurational sampling in generalized statistical ensembles, with very high quality synchrotron X-ray diffraction data, the molecular mass of the crystallizing oligomer was first singled out, and its structure was then determined with a high degree of accuracy. The original procedures and methods developed for this particular case can be considered a suitable reference to tackle the difficult characterization problems posed by the crystalline powders of organic materials in general

Enhanced Vertical Concentration Gradient in Rubbed P3HT:PCBM Graded Bilayer Solar Cells

Graded bilayer solar cells have proven to be at least as efficient as the bulk heterojunctions when it comes to the Poly­(3-hexylthiophene) (P3HT) - [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) donor–acceptor system. However, control of the vertical concentration gradient using simple techniques has never been reported. We demonstrate that rubbing the P3HT layer prior to PCBM deposition induces major morphological changes in the active layer. Using the newly introduced energy-dispersive X-ray spectroscopy element mapping technique, we found that rubbing P3HT induces the formation of an ideal vertical donor–acceptor concentration gradient. Furthermore, the P3HT crystallites undergo a molecular reorientation from edge-on to face-on configuration inducing a better charge transport in the vertical direction. The combination of these two major morphological changes leads to the fabrication of high-performance solar cells that exhibit, to date, the record efficiencies for spin-coated graded bilayers solar cells

Interaction of Polar and Nonpolar Polyfluorenes with Layers of Two-Dimensional Titanium Carbide (MXene): Intercalation and Pseudocapacitance

This article provides insight into the interaction of synthetic conjugated polymers [polyfluorene derivatives (PFDs)] with layers of two-dimensional titanium carbide (Ti₃C₂T_<i>x</i>). Three derivatives with nonpolar, polar, and charged nitrogen-containing functionalities were synthesized via the Suzuki polycondensation reaction. The organic–inorganic PFD/Ti₃C₂T_<i>x</i> hybrids were prepared and characterized using X-ray diffraction and a range of microscopic and spectroscopic techniques to elucidate the host–guest interaction mechanism. We show that polar polymers with charged nitrogen-containing ends have the strongest interaction with the Ti₃C₂T_<i>x</i> layers, yielding an increase in interlayer spacing and large shifts in spectroscopic peaks. Furthermore, the effect of polymer backbone juxtaposition between Ti₃C₂T_<i>x</i> layers on pseudocapacitance is discussed in detail. Our results suggest that new organic materials capable of intercalation between the layers of Ti₃C₂T_<i>x</i> and other MXenes may be used in the design of hybrid structures for high-performance energy storage applications and beyond