Efficient Blue, Green, and Red Electroluminescence from Carbazole-Functionalized Poly(spirobifluorene)s

Tunable Fluorescence, Morphology, and Antibacterial Behaviors of Conjugated Oligomers via Host-Guest Supramolecular Self-Assembly

Host-guest supramolecular self-assembly has become one facile but efficient way to regulate the optical properties of conjugated oligomers and construct promising photofunctional materials. Herein, we design two linear conjugated oligomers terminated with two or four pyridinium moieties, which show different 1:1 'head-to-tail' binding patterns with cucurbit[8]uril (CB[8]) to form host-guest supramolecules. After being encapsulated in the hydrophobic cavity of the CB[8] host, the fluorescence emission of the conjugated oligomers undergoes significant changes, resulting in tunable fluorescence color with enhanced quantum yields. Triggered by the aggregation of supramolecules, the regular or rigid binding modes lead to the formation of cuboids and spheroids in nanoscale, respectively. Due to the macrocyclic-confinement effect, the light-driven reactive oxygen species (ROS) production of the host-guest complex is increased significantly, thereby improving the photodynamic antibacterial performance toward Staphylococcus aureus (S. aureus).

Phosphine-Oxide-Balanced Intra- and Interchain Through-Space Charge Transfer in Thermally Activated Delayed Fluorescence Polymers: Beyond 30% External Quantum Efficiency

Through-space charge transfer (TSCT) is crucial for developing highly efficient thermally activated delayed fluorescence polymers. The balance of intra- and interchain TSCT can markedly improve performance, but it is still a big challenge. In this work, an effective strategy for "intra- and interchain TSCT balance" is demonstrated by way of a series of non-conjugated copolymers containing a 9,9-dimethylacridine donor and triazine-phosphine oxide (PO)-based acceptors. Steady-state and transient emission spectra indicate that compared to the corresponding blends, the copolymers can indeed achieve balanced intra- and interchain TSCT by accurately optimizing the inductive and steric effects of the acceptors. The DPOT acceptor with the strongest electron-withdrawing ability and the second bigger steric hindrance endows its copolymers with state-of-the-art photoluminescence and electroluminescence quantum efficiencies beyond 95% and 32%, respectively. This demonstrates that, compared to other congeners, the synergistic inductive and steric effects effectively enhance TSCT in DPOT-based copolymers for radiation, and suppress singlet and triplet quenching. The record-high efficiencies of its devices make this kind of copolymers hold the potential for low-cost, large-scale, and high-efficiency applications.

Controlling Molecular Aggregation-Induced Emission by Controlled Polymerization

In last twenty years, the significant development of AIE materials has been witnessed. A number of small molecules, polymers and composites with AIE activity have been synthesized, with some of these exhibiting great potential in optoelectronics and biomedical applications. Compared to AIE small molecules, macromolecular systems-especially well-defined AIE polymers-have been studied relatively less. Controlled polymerization methods provide the efficient synthesis of well-defined AIE polymers with varied monomers, tunable chain lengths and narrow dispersity. In particular, the preparation of single-fluorophore polymers through AIE molecule-initiated polymerization enables the systematic investigation of the structure-property relationships of AIE polymeric systems. Here, the main polymerization techniques involved in these polymers are summarized and the key parameters that affect their photophysical properties are analyzed. The author endeavored to collect meaningful information from the descriptions of AIE polymer systems in the literature, to find connections by comparing different representative examples, and hopes eventually to provide a set of general guidelines for AIE polymer design, along with personal perspectives on the direction of future research.

Organic Semiconductor Micro/Nanocrystals for Laser Applications

Organic semiconductor micro/nanocrystals (OSMCs) have attracted great attention due to their numerous advantages such us free grain boundaries, minimal defects and traps, molecular diversity, low cost, flexibility and solution processability. Due to all these characteristics, they are strong candidates for the next generation of electronic and optoelectronic devices. In this review, we present a comprehensive overview of these OSMCs, discussing molecular packing, the methods to control crystallization and their applications to the area of organic solid-state lasers. Special emphasis is given to OSMC lasers which self-assemble into geometrically defined optical resonators owing to their attractive prospects for tuning/control of light emission properties through geometrical resonator design. The most recent developments together with novel strategies for light emission tuning and effective light extraction are presented.

Improving the Performance of Blue Polymer Light-Emitting Diodes Using a Hole Injection Layer with a High Work Function and Nanotexture

For light-emitting polymers with a deep highest occupied molecular orbital energy level used for polymer light-emitting diodes (PLEDs), the hole injection barrier and hole transport of the anode buffer layer are of vital importance for optimizing electroluminescent performance. In this study, high-work-function hole injection layers with nanotextures were achieved by modifying poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) with a perfluorinated ionomer (PFI) and n-butyl alcohol and were used to achieve a single-layer device without a hole transport layer. With such an interlayer, the PLEDs based on PPF-SO25 exhibit remarkable current efficiency over 13.0 cd A^-1, which significantly outperform the devices with regular PEDOT:PSS. To our knowledge, this performance is among the best reported for single-layer blue PLEDs. The bias-dependent capacitance curves of these PLEDs suggest a nonuniform surface distribution of PFI. Our findings show that the PFI-modified PEDOT:PSS not only operates as a high-work-function hole injection layer to facilitate hole injection but also as a potential inner scattering medium for light extraction.

Improving the Electroluminescent Performance of Blue Light-Emitting Polymers by Side-Chain Modification

Blue light-emitting polymers are in urgent demand for new-generation display and solid-state lighting devices fabricated through low-cost wet processing. However, their current performances are far from satisfactory. Here, we developed a series of poly(fluorene-co-dibenzothiophene-S,S-dioxides) (PFSOs) bearing different alkyl chains, alkoxyphenyl chains, or both alkylaryl and alkoxyphenyl side chains. The introduction of alkoxyphenyl groups moderately enhanced the electron-donating ability of the polymers, leading to more balanced charge carrier fluxes. Meanwhile, asymmetric bulky side chains enabled more pronounced variation of molecular conformation while restraining the intermolecular aggregation of polymers, resulting in a lower refractive index, thus facilitating light extraction compared with polymers based on the same two alkyl or alkoxyphenyl side chains. Polymer light-emitting devices based on PFSO-BMD with asymmetric side chains exhibited a maximum luminous efficiency of 8.58 cd A^-1, associated with pure blue Commission Internationale de l'Eclairage coordinates of (0.14, 0.14). These findings demonstrated that side-chain modification can be an effective strategy for developing efficient solution-processable blue light-emitting polymers.

Synthesis and Electroluminescent Properties of Through-Space Charge Transfer Polymers Containing Acridan Donor and Triarylboron Acceptors

We report the design, synthesis and electroluminescent properties of three kinds of through-space charge transfer (TSCT) polymers consisting of non-conjugated polystyrene backbone, acridan donor and triarylboron acceptors having different substituents such as hydrogen (H), fluorine (F), and trifluoromethyl (CF₃). Owing to the weak electron interaction between acridan donor and triarylboron acceptor through non-conjugated connection, blue emission with peaks in range of 429–483 nm can be achieved for the polymers in solid-state film, accompanied with photoluminescence quantum yields of 26–53%. The resulting TSCT polymers exhibit small ΔE_ST values below 0.1 eV owing to the separated HOMO and LUMO distributions, showing thermally activated delayed fluorescence with lifetimes in range of 0.19–0.98 μs. Meanwhile, the polymers show aggregation-induced emission (AIE) effect with the emission intensity increased by up to ~33 folds from solution to aggregation state. Solution-processed organic light-emitting diodes based on the polymers containing trifluoromethyl substituent exhibit promising electroluminescent performance with maximum luminous efficiency of 20.1 cd A⁻¹ and maximum external quantum efficiency of 7.0%, indicating that they are good candidates for development of luminescent polymers.

Conductivity and Density of States of New Polyphenylquinoline

Electrical, photoelectrical, and optical properties of thin films of a new heat-resistant polyphenylquinoline synthesized using facile methods were investigated. An analysis of the obtained temperature dependences of the dark conductivity and photoconductivity indicates the hopping mechanism of conductivity over localized states arranging at the energy distance of 0.8 eV from the Fermi level located inside the band gap of the investigated material. The optical band gap of the studied material was estimated from an analysis of the spectral dependences of the photoconductivity and absorption coefficient before (1.8–1.9 eV) and after (2.0–2.2 eV) annealing at temperatures exceeding 100 °C. The Gaussian character of the distribution of the localized states of density inside the band gap near the edges of the bands was established. A mechanism of changes in the optical band gap of the investigating polymer under its annealing is proposed.

Developing Through-Space Charge Transfer Polymers as a General Approach to Realize Full-Color and White Emission with Thermally Activated Delayed Fluorescence

Through-space charge transfer polymers (TSCT polymers) that contain a non-conjugated polystyrene backbone and spatially separated donor and acceptor units for solution-processed OLEDs with full-color and white emission is reported. By tuning the charge transfer strength between donor and acceptors with different electron-accepting ability, emission color spanning from deep blue to red can be achieved. By incorporating two kinds of donor/acceptor pairs in one polymer to create duplex through-space charge-transfer channels, blue and yellow emission can be simultaneously obtained to realize white electroluminescence from a single polymer. The TSCT polymers exhibit thermally activated delayed fluorescence effect with delayed-component lifetimes in range of 0.36-1.98 μs, and unexpected aggregation-induced emission (emission intensity enhancement of up to 117 from solution to aggregation state).

Effect of side chains on color purities of mono-triphenylamine-functionalized polyspirobifluorenes for pure blue polymer light-emitting diodes

Large and rigid substituents may facilitate the improvement of the color purity of polyfluorenes.