No abstract

The exploitation of deep-blue polymeric emitters is of great importance for the application of solution-processed organic light-emitting diodes (OLEDs) in full color display. The highly efficient deep-blue thermally activated delayed fluorescence (TADF) polymers are rarely reported up to now. Herein, we developed a series of deep-blue TADF polymers to fabricate highly efficient nondoped solution-processed OLEDs. By incorporating appropriate host with high triplet energy and deep-blue emitter with high fluorescent efficiency, the polymers are endowed with distinct TADF features. Using these deep-blue polymeric emitters, the nondoped single polymer based OLEDs achieve a maximum external quantum efficiency of 5.3% with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.15, 0.09), which represents the state-of-the-art device performance for the TADF-based deep-blue polymer light-emitting diodes (PLEDs).

Dative bonds between p- and d-block atoms are common but species containing a double dative bond, which donate two-electron pairs to the same acceptor, are far less common. The synthesis of complexes between UCl4 and carbodiphosphoranes (CDP), which formally possess double dative bonds Cl4U⇇CDP, is reported in this paper. Single-crystal X-ray diffraction shows that the uranium−carbon distances are in the range of bond lengths for uranium−carbon double bonds. A bonding analysis suggests that the molecules are uranium−carbone complexes featuring divalent carbon(0) ligands rather than uranium−carbene species. The complexes represent rare examples with a double dative bond in f-block chemistry. Our study not only introduces the concept of double dative bonds between carbones and f-block elements but also opens an avenue for the construction of other complexes with double dative bonds, thus providing new opportunities for the applications of f-block compounds.

The properties of semicrystalline polymeric materials depend remarkably on their structures, especially for those exhibiting a polymorphic behavior. This offers an efficient way to tailor their properties through crystal engineering. For control of the crystal structure, and therefore the physical and mechanical properties, a full understanding of the polymorph selection of polymers under varied conditions is essential. This has stimulated a mass of research work on the polymorphic crystallization and related phase transformation. Considering that the isotactic poly(1-butene) (iPBu) exhibits pronounced polymorphs and complicated transition between different phases, the study on its crystallization and phase transformation has attracted considerable attention during the past decades. This review provides the context of the recent progresses made on the crystallization and phase transition behavior of iPBu. We first review the crystal structures of known crystal forms and then their formation conditions and influencing factors. In addition, the inevitable form II to form I spontaneous transition mechanism and the transformation kinetics is reviewed based on the existing research works, aiming for it to be useful for its processing in different phases and the further technical development of new methods for accelerating or even bypass its form II to form I transformation.

Thin films of isotactic polybutene-1 (iPBu) with large lathlike flaton form II crystals were prepared by isothermal crystallization from melt at 105 °C. The II−I phase transition of this kind of thin film was investigated by Fourier transform infrared spectroscopy, transmission electron microscopy, and atomic force microscopy (AFM). Spectroscopy results show that the phase transition starts immediately after cooling down to −10 °C. The phase transformation propagates quickly in the first 10 min but then slows down and reaches a plateau by further annealing at this temperature. Another quick transformation process has been realized by heating the related sample to room temperature. This has been associated with the nucleation and crystal growth processes of the phase transition and confirmed here by the morphological study. It has been confirmed by AFM that, at the early stage of II−I phase transition that happened at −10 °C, the formed form I crystals are too small to be visualized by AFM. With increasing aging time at room temperature, some form I iPBu crystals appear mostly at the edges of the flat-on crystalline sheet. These crystals grow further with time until the complete transformation of the individual whole sheet. This provides morphological evidence for the nucleation and crystal growth events during II−I phase transition of iPBu.