Hierarchical Uniform Supramolecular Conjugated Spherulites with Suppression of Defect Emission

Triphenylamine Spirofunctionalized Light-Emitting Conjugated Polymer with an Ultradeep-Blue Narrowband Emission for Large-Area Printed Display

Emerging printed large-area polymer light-emitting diodes (PLEDs) are essential for manufacturing flat-panel displays and solid lighting devices. However, it is challenging to obtain large-area and stable ultradeep-blue PLEDs because of the lack of light-emitting conjugated polymers (LCPs) with robust deep-blue emissions, excellent morphological stabilities, and high charging abilities. Here, a novel unsymmetrically substituted polydiarylfluorene (POPSAF) is obtained with stable narrowband emission for large-area printed displays via triphenylamine (TPA) spirofunctionalization of LCPs. POPSAF films show narrowband and stable ultradeep-blue emission with a full width at half maximum (FWHM) of 36 nm, associated with their intrachain excitonic behavior without obvious polaron formation. Compared to controlled poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]-co-[5-(octyloxy)-9,9-diphenylfluoren-2,7-diyl] (PODPF), excellent charge transport is observed in the POPSAF films because of the intrinsic hole transport ability of the TPA units. Large-area PLEDs are fabricated via blade-coating with an emission area of 9 cm2, which exhibit uniform ultradeep-blue emission with an FWHM of 36 nm and corresponding Commission internationale de l'éclairage (CIE) coordinates of (0.155, 0.072). These findings are attributed to the synergistic effects of robust emission, stable morphology, and printing capacity. Finally, preliminary printed passive matrix (PM) PLED displays with 20 × 20 pixels monochromes are fabricated, confirmed the effectiveness of spirofunctionalization in optoelectronics.

J-Aggregate Promoting NIR-II Emission for Fluorescence/Photoacoustic Imaging-Guided Phototherapy

J-aggregate is a promising strategy to enhance second near-infrared window (NIR-II) emission, while the controlled synthesis of J-aggregated NIR-II dyes is a huge challenge because of the lack of molecular design principle. Herein, bulk spiro[fluorene-9,9'-xanthene] functionalized benzobisthiadiazole-based NIR-II dyes (named BSFX-BBT and OSFX-BBT) are synthesized with different alkyl chains. The weak repulsion interaction between the donor and acceptor units and the S…N secondary interactions make the dyes to adopt a co-planar molecular conformation and display a peak absorption >880 nm in solution. Importantly, BSFX-BBT can form a desiring J-aggregate in the condensed state, and femtosecond transient absorption spectra reveal that the excited states of J-aggregate are the radiative states, and J-aggregate can facilitate stimulated emission. Consequently, the J-aggregated nanoparticles (NPs) display a peak emission at 1124 nm with a high relative quantum yield of 0.81%. The efficient NIR-II emission, good photothermal effect, and biocompatibility make the J-aggregated NPs demonstrate efficient antitumor efficacy via fluorescence/photoacoustic imaging-guided phototherapy. The paradigm illustrates that tuning the aggregate states of NIR-II dye via spiro-functionalized strategy is an effective approach to enhance photo-theranostic performance.

Ultraviolet Organic Laser from Rhombus Microcrystal: Benefits of Single-Molecule Emission from Twisted Structure

Light-emitting molecular crystals with efficient emission behavior are crucial for fabricating low-threshold ultraviolet organic lasers. Herein, we demonstrated a rhombus microcrystal from a fluorene-based conjugated molecule (CL-1) with robust emission behavior for an ultraviolet organic laser. Due to the synergistic effect of twisted intramolecular conformation and weak π-interaction, the CL-1 single crystal showed an extremely high photoluminescence quantum yield (PLQY) of ∼82%, due to their single-molecule excitonic behavior. Considering the diverse noncovalent interactions, CL-1 molecules easily self-assembled into the rhombus microcrystals. Finally, a low-threshold ultraviolet organic laser was fabricated with a sharp emission at 379 nm, attributed to the 0-1 vibration band of a single CL-1 molecule, also further confirming the single twisted-molecule emission in crystal states. Precisely controlling the intramolecular twisted structure and intermolecular interaction of organic conjugated molecules is a precondition to obtain robust ultraviolet emission for optoelectronic applications.

Coplanar Conformational Structure of π-Conjugated Polymers for Optoelectronic Applications

Hierarchical structure of conjugated polymers is critical to dominating their optoelectronic properties and applications. Compared to nonplanar conformational segments, coplanar conformational segments of conjugated polymers (CPs) demonstrate favorable properties for applications as a semiconductor. Herein, recent developments in the coplanar conformational structure of CPs for optoelectronic devices are summarized. First, this review comprehensively summarizes the unique properties of planar conformational structures. Second, the characteristics of the coplanar conformation in terms of optoelectrical properties and other polymer physics characteristics are emphasized. Five primary characterization methods for investigating the complanate backbone structures are illustrated, providing a systematical toolbox for studying this specific conformation. Third, internal and external conditions for inducing the coplanar conformational structure are presented, offering guidelines for designing this conformation. Fourth, the optoelectronic applications of this segment, such as light-emitting diodes, solar cells, and field-effect transistors, are briefly summarized. Finally, a conclusion and outlook for the coplanar conformational segment regarding molecular design and applications are provided.

Polyferrocenylsilane Block Copolymer Spherulites in Dilute Solution

Self-assembly of block copolymers (BCP) into uniform 3D structures in solution is an extremely rare phenomenon. Furthermore, the investigation of general prerequisites for fabricating a specific uniform 3D structure remains unknown and challenging. Here, through a simple one-pot direct self-assembly (heating and cooling) protocol, we show that uniform spherulite-like structures and their precursors can be prepared with various poly(ferrocenyldimethylsilane) (PFS) BCPs in a variety of polar and non-polar solvents. These structures all evolve from elongated lamellae into hedrites, sheaf-like micelles, and finally spherulites as the annealing temperature and supersaturation degree are increased. The key feature leading to this growth trajectory is the formation of secondary crystals by self-nucleation on the surface of early-elongated lamellae. We identified general prerequisites for fabricating PFS BCP spherulites in solution. These include corona/PFS core block ratios in the range of 1-5.5 that favor the formation of 2D structures as well as the development of secondary crystals on the basal faces of platelets at early stages of the self-assembly. The one-pot direct self-assembly provides a general protocol to form uniform spherulites and their precursors consisting of PFS BCPs that match these prerequisites. In addition, we show that manipulation of various steps in the direct self-assembly protocol can regulate the size and shape of the structures formed. These general concepts show promise for the fabrication and optimization of spherulites and their precursors from semicrystalline BCPs with interesting optical, electronic, or biomedical properties using the one-pot direct self-assembly protocol.

Unveiling the Effects of Interchain Hydrogen Bonds on Solution Gelation and Mechanical Properties of Diarylfluorene-Based Semiconductor Polymers

The intrinsically rigid and limited strain of most conjugated polymers has encouraged us to optimize the extensible properties of conjugated polymers. Herein, learning from the hydrogen bonds in glucose, which were facilitated to the toughness enhancement of cellulose, we introduced interchain hydrogen bonds to polydiarylfluorene by amide-containing side chains. Through tuning the copolymerization ratio, we systematically investigated their influence on the hierarchical condensed structures, rheology behavior, tensile performances, and optoelectronic properties of conjugated polymers. Compared to the reference copolymers with a low ratio of amide units, copolymers with 30% and 40% amide units present a feature of the shear-thinning process that resembled the non-Newtonian fluid, which was enabled by the interchain dynamic hydrogen bonds. Besides, we developed a practical and universal method for measuring the intrinsic mechanical properties of conjugated polymers. We demonstrated the significant impact of hydrogen bonds in solution gelation, material crystallization, and thin film stretchability. Impressively, the breaking elongation for P4 was even up to ~30%, which confirmed the partially enhanced film ductility and toughness due to the increased amide groups. Furthermore, polymer light-emitting devices (PLEDs) based on these copolymers presented comparable performances and stable electroluminescence (EL). Thin films of these copolymers also exhibited random laser emission with the threshold as low as 0.52 μJ/cm², suggesting the wide prospective application in the field of flexible optoelectronic devices.

Phase Behavior of Amorphous/Semicrystalline Conjugated Polymer Blends

We report the phase behavior of amorphous/semicrystalline conjugated polymer blends composed of low bandgap poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene) -alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) and poly{(N,N′-bis(2-octyldodecyl)naphthalene -1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)). As usual in polymer blends, these two polymers are immiscible because ΔS_m ≈ 0 and ΔH_m > 0, leading to ΔG_m > 0, in which ΔS_m, ΔH_m, and ΔG_m are the entropy, enthalpy, and Gibbs free energy of mixing, respectively. Specifically, the Flory–Huggins interaction parameter (χ) for the PCPDTBT /P(NDI2OD-T2) blend was estimated to be 1.26 at 298.15 K, indicating that the blend was immiscible. When thermally analyzed, the melting and crystallization point depression was observed with increasing PCPDTBT amounts in the blends. In the same vein, the X-ray diffraction (XRD) patterns showed that the π-π interactions in P(NDI2OD-T2) lamellae were diminished if PCPDTBT was incorporated into the blends. Finally, the correlation of the solid-liquid phase transition and structural information for the blend system may provide insight for understanding other amorphous/semicrystalline conjugated polymers used as active layers in all-polymer solar cells, although the specific morphology of a film is largely affected by nonequilibrium kinetics.

Novel Conjugated Side Chain Fluorinated Polymers Based on Fluorene for Light-Emitting and Ternary Flash Memory Devices

Three novel conjugated polymers based on 9,9'-dioctylfluorene unit and isoindolo[2,1-a]benzimidazol-11-one with different fluorine substituents (0, 2 and 4) were synthesized. PLED and resistive memory devices based on these polymers were prepared consequently. PLED based on four-fluorinated polymer showed the highest maximum brightness of 3192 cd m-2 with almost 5-fold increase of current efficiency 8-fold increase of external quantum efficiency compared to that of the other two, and all the PLEDs exhibited good emission stability with no noticeable change of electroluminescence even under high voltage of 10 V. The memory device of doubly-fluorinated polymer exhibited ternary flash behavior with threshold voltages below -2.5 V, while device of four-fluorinated polymer possessed ON/OFF current ratio above 104. Impact of fluorine substitutions on the performance of devices were briefly investigated. The results revealed that the improvement of device performance might not scale with the increasing number of fluorine substitutions, and the four-fluorine-substituted polymer and doubly-fluorinated polymer could be encouraging materials for applications of PLED and resistive memory device and worth of further design of other new polymer systems.