Synthetic Concept of Intrinsically Elastic Luminescent Polyfluorene-Based Copolymers via RAFT Polymerization

Elastic-Plastic Fully π-Conjugated Polymer with Excellent Energy Dissipation Capacity for Ultra-Deep-Blue Flexible Polymer Light-Emitting Diodes with CIEy = 0.04

Emerging intrinsically flexible fully π-conjugated polymers (FπCPs) are a promising functional material for flexible optoelectronics, attributed to their potential interchain interpenetration and entanglement. However, the challenge remains in obtaining elastic-plastic FπCPs with intrinsic robust optoelectronic property and excellent long-term and cycling deformation stability simultaneously for applications in deep-blue flexible polymer light-emitting diodes (PLEDs). This study, demonstrates a series of elastic-plastic FπCPs (P1-P4) with an excellent energy dissipation capacity via side-chain internal plasticization for the ultra-deep-blue flexible PLEDs. First, the freestanding P1 film exhibited a maximum fracture strain of 34.6%. More interestingly, the elastic behavior is observed with a low strain (≤10%), and the stretched film with a high deformation (>10%) attributed to plastic processing revealed the robust capacity to realize energy absorption and release. The elastic-plastic P1 film exhibits outstanding ultra-deep-blue emission, with an efficiency of 56.38%. Subsequently, efficient PLEDs are fabricated with an ultra-deep-blue emission of CIE (0.16, 0.04) and a maximum external quantum efficiency of 1.73%. Finally, stable and efficient ultra-deep-blue electroluminescence are obtained from PLEDs based on stretchable films with different strains and cycling deformations, suggesting excellent elastic-plastic behavior and deformation stability for flexible electronics.

Synthesis and Electron Transporting Properties of Diblock Copolymers Consisting of Polyfluorene and Polystyrene

Poly(9,9-di-n-octylfluorene) (PFO) is a promising material for polymer light-emitting diodes (PLEDs) due to its advantageous properties. To enhance its electron transporting capabilities, diblock polymers were synthesized by attaching polystyrene (PSt) chains of varying lengths to one end of the PFO molecule. In a comparative study with PFO homopolymer, the diblock polymers maintained similar thermal properties, absorption spectra, and photoluminescent stability, while exhibiting slightly deeper lowest unoccupied molecular orbital (LUMO) levels and higher crystallinity. Notably, diblock polymers with shorter polystyrene blocks demonstrated higher electron mobility than the PFO homopolymer and diblock polymers with excessively long polystyrene blocks. These findings suggest that the optimal chain length of the polystyrene block is crucial for maximizing electron mobility, thus offering valuable insights for designing high-performance PLED materials.

A Holistic Review of C = C Crosslinkable Conjugated Molecules in Solution-Processed Organic Electronics: Insights into Stability, Processibility, and Mechanical Properties

Solution-processable organic conjugated molecules (OCMs) consist of a series of aromatic units linked by σ-bonds, which present a relatively freedom intramolecular motion and intermolecular re-arrangement under external stimulation. The cross-linked strategy provides an effective platform to obtain OCMs network, which allows for outstanding optoelectronic, excellent physicochemical properties, and substantial improvement in device fabrication. An unsaturated double carbon-carbon bond (C = C) is universal segment to construct crosslinkable OCMs. In this review, the authors will set C = C cross-linkable units as an example to summarize the development of cross-linkable OCMs for solution-processable optoelectronic applications. First, this review provides a comprehensive overview of the distinctive chemical, physical, and optoelectronic properties arising from the cross-linking strategies employed in OCMs. Second, the methods for probing the C = C cross-linking reaction are also emphasized based on the perturbations of chemical structure and physicochemical property. Third, a series of model C = C cross-linkable units, including styrene, trifluoroethylene, and unsaturated acid ester, are further discussed to design and prepare novel OCMs. Furthermore, a concise overview of the optoelectronic applications associated with this approach is presented, including light-emitting diodes (LEDs), solar cells (SCs), and field-effect transistors (FETs). Lastly, the authors offer a concluding perspective and outlook for the improvement of OCMs and their optoelectronic application via the cross-linking strategy.

Internal conversion rate constant calculations considering Duschinsky, anharmonic and Herzberg-Teller effects

A novel method for calculating rate constants for internal conversion (k_IC) that simultaneously accounts for Duschinsky, anharmonic and Herzberg-Teller effects has been developed and implemented. This method has been applied to robust planar molecules like tetraoxa[8]circulene (4B), free-base porphyrin (H2P) and pyrometene (PM567) with small Duschinsky rotation (i.e. with almost identical normal coordinates in the ground and excited states) and to poly[n]fluorenes (P[n]F) (n = 2-14) with a substantial Duschinsky rotation. The obtained results show that the Duschinsky effect is large in the harmonic approximation, whereas it is in general much smaller in the anharmonic approximation. The Duschinsky effect is found to be large for high frequency vibrational modes with energies of ∼3300 cm^-1 such as the X-H (X = C, N and O) stretching modes that mix in the S₁ → S₀ electronic transition. However, even in this case, the increase in k_IC due to the Duschinsky effect does not exceed one order of magnitude. The calculations show that anharmonic contributions to k_IC are larger than Herzberg-Teller contributions which in turn are larger than contributions from the Duschinsky effect ANH > HT > Du. We also show that an approximation, where only X-H bonds are considered in the k_IC calculation, is accurate even for P[n]F (n = 2-14).

Intrinsically Stretchable Electroluminescent Elastomers with Self-Confinement Effect for Highly Efficient Non-Blended Stretchable OLEDs

Ultra-flexible stretchable organic light-emitting diodes (OLEDs) are emerging as a basic component of flexible electronics and human-machine interfaces. However, the brightness and efficiency of stretchable OLEDs remain still far inferior to their rigid counterparts, owing to the scarcity of satisfactory stretchable electroluminescent materials. Herein, we explore a general concept based on the self-confinement effect to dramatically improve the stretchability of elastomers, without affecting electroluminescent properties. The balanced rigid/flexible chain dynamics under self-confinement significantly reduces the modulus of the elastomers, resulting in the maximum strain reaching 806 %. Ultra-flexible stretchable OLEDs have been constructed based on the resulting ISEEs, achieving unprecedented high-performance non-blended stretchable OLEDs. The results suggest an effective molecular design strategy for highly deformable stretchable displays and flexible electronics.

Improving the Intrinsic Stretchability of Fully Conjugated Polymer for Deep-Blue Polymer Light-Emitting Diodes with a Narrow Band Emission: Benefits of Self-Toughness Effect

It is challenging to construct the intrinsically stretchable active layer of rigid conjugated polymers (CPs) toward flexible deep-blue light-emitting diodes (FLEDs). Inspired by the self-toughness effect, sacrificial hydrogen bonding (H-bonding) and a cross-linked network synergistically enabled polydiarylfluorene (PFs-NH) films to present efficient deep-blue emission and excellent intrinsic stretchability. In particular, a cross-linked network structure presenting viscoelasticity behaviors, which was successfully inherited into postprocessed films with interchain interpenetration and a crystallinity domain and behaved as energy absorption and dissipation centers, was induced by the interchain H-bonding interaction in toluene (Tol) precursor solutions where the storage moduli (G') gradually exceeded the loss moduli (G″). Subsequently, intrinsic stretchable films with a tensile rate of 30% were prepared from Tol solutions, different from the brittle films from polar solvents. Eventually, narrow band, deep-blue PLEDs showed a maximum EQE of 1.28% and a full width half-maximum (fwhm) of 28 nm. Therefore, the self-toughness effect induced by hierarchical structures will be feasible to obtain high-performance FLEDs.

A Self-Assembled 3D Penetrating Nanonetwork for High-Performance Intrinsically Stretchable Polymer Light-Emitting Diodes

The emergence of wearable technology can significantly benefit from electronic displays fabricated using intrinsically stretchable (is-) materials. Typically, an improvement in the stretchability of conventional light-emitting polymers is accompanied by a decrease in charge transportability, thus resulting in a significant decrease in device efficiency. In this study, a self-assembled 3D penetrating nanonetwork is developed to achieve increased stretchability and mobility simultaneously, based on high-molecular-weight phenylenevinylene (L-SY-PPV) and polyacrylonitrile (PAN). The mobility of L-SY-PPV/PAN increases by 5-6 times and the stretchability increases from 20% (pristine L-SY-PPV film) to 100%. A high current efficiency (CE) of 8.13 cd A^-1 is observed in polymer light-emitting diodes (PLEDs) fabricated using 40% stretched L-SY-PPV/PAN. Furthermore, using a polyethyleneimine ethoxylated (PEIE), an 1,10-phenanthroline monohydrate (pBphen), and a reduced Triton X-100 (TR) chelated Zn-based is- electron-injection layer of Zn-PEIE-pBphen-TR, an is-PLED is realized with a turn-on voltage of 6.5 V and a high CE of 2.35 cd A^-1 . These results demonstrate the effectiveness of using the self-assembled 3D penetrating nanonetwork for the fabrication of is-PLEDs.

Intrinsically flexible displays: key materials and devices

Continuous progress in flexible electronics is bringing more convenience and comfort to human lives. In this field, interconnection and novel display applications are acknowledged as important future directions. However, it is a huge scientific and technical challenge to develop intrinsically flexible displays due to the limited size and shape of the display panel. To address this conundrum, it is crucial to develop intrinsically flexible electrode materials, semiconductor materials and dielectric materials, as well as the relevant flexible transistor drivers and display panels. In this review, we focus on the recent progress in this field from seven aspects: background and concept, intrinsically flexible electrode materials, intrinsically flexible organic semiconductors and dielectric materials for organic thin film transistors (OTFTs), intrinsically flexible organic emissive semiconductors for electroluminescent devices, and OTFT-driven electroluminescent devices for intrinsically flexible displays. Finally, some suggestions and prospects for the future development of intrinsically flexible displays are proposed.

The Impacts of Polyisoprene Physical Interactions on Sorting of Single-Wall Carbon Nanotubes

Conjugated polymer sorting is currently the best method to select large-diameter single-walled carbon nanotubes (SWCNTs) with tunable narrow chirality in the adaption of highly desired electronics applications. The acceleration on conjugated polymers-SWCNTs interaction with long-term stability through different molecular designs; for example, longer alkyl side-chains or conjugation moieties have been extensively developed in recent years. However, the importance of the macromolecules with abundant van der Waals (VDW) interaction in the conjugated-based block copolymer system acting during SWCNTs sorting is not clearly demonstrated. In this work, a conjugated diblock copolymer involving polyisoprene (PI) and highly dense π-interaction of poly (9,9-dioctylfluorene) (PFO) is utilized to investigate the impact of natural rubber PI physical interaction on sorting effectiveness and stability. Through the rational design of diblock copolymer, PFO with ≈1200 isoprene units can remarkably enhance SWCNTs sorting ability and selected few chiralities with a diameter of ≈0.83-1.1 nm and highly stable solution for more than 1 year. The introduction of long-chain PI system is attributed not only to form weak VDW force with SWCNTs and strengthen the wrapping of PFO around the semiconducting SWCNTs but also to act as a barrier among nanotubes to prevent reaggregation of sorted SWCNTs.

Suzuki–Miyaura catalyst-transfer polycondensation of triolborate-type fluorene monomer: toward rapid access to polyfluorene-containing block and graft copolymers from various macroinitiators

We demonstrated that the Suzuki–Miyaura catalyst transfer polycondensation of a triolborate-type fluorene monomer can be an efficient and versatile approach to the synthesis of polyfluorenes (PFs) and PF-containing block and graft copolymers.