Multiple σ–π Conjugated Molecules with Selectively Enhanced Electrical Performance for Efficient Solution‐Processed Blue Electrophosphorescence

Abstract

Phosphorescent organic light-emitting diodes (PhOLEDs) have attracted intense attention owing to their theoretical 100% internal quantum efficiency through simultaneously utilizing singlet and triplet excitons. [1] With the tremendous efforts over the past few decades, the thermalevaporated electrophosphorescence devices with excellent external quantum efficiencies (EQEs) and operation lifetimes have been achieved. [2][3][4][5][6] Nevertheless, the development of high-efficiencies blue PhOLEDs remains as a daunting and forbidden challenge although blue emission is indispensable to improve color rendering index and color gamuts. [7][8][9][10][11][12] Moreover, the vacuum-deposited PhOLEDs require complicated technological processes and precisely controlling of concentrations of different materials in emission layer (EML) for realizing high device performance, which leads to relatively high fabrication costs. Solution-processed PhOLEDs based on spin-coating, blade coating and/or inkjet printing have been introduced with insistence because of their ultimate potential in facilitating largearea, low-cost, and high-efficiency flat-panel display as well as lighting products. [13,14] However, it is still quite difficult to develop solution-processed organic semiconductors simultaneously with the characteristics of good-solubility, large bandgap, and good carrier transportation for high-performance solutionprocessed blue PhOLEDs, which are fundamentally important for next-generation lighting sources and displays technologies.Commonly, the host-dopant systems are generally adopted to controllably eliminate the triplet-involved quench effects of emissive phosphors in the PhOLEDs. [15] The basic metrics of solution-processed hosts are excellent electrical property for endowing efficient and balanced carrier injection and flux, and high triplet energy (E T ) levels for maintaining exothermic energy migration from the hosts to dopants and confining the triplet excitons in EML. [16,17] Furthermore, additional requirements of hosts have to be simultaneously fulfilled to support high-efficiency solution-processed PhOLEDs: [18,19] i) good solubility in common organic solvent to fabricate stable, uniform and pin-hole free films, ii) high thermal and chemical stability to endow high temperature thermal annealing for eliminating Selectively and controllably regulating molecular functions of organic optoelectronic materials with high solubility for solution-processible devices is highly desired but remains as one of the most significant challenges in material science. Here, a concise molecular design strategy is reported to achieve effective electronic communications using efficient d-orbital participated σ-π conjugations between Si and π unit for purposely modulating the electrical properties of organic optoelectronic materials. Through a two-step reaction in high yield, DSiDCzSi with the enhanced σ-π conjugation is facilely constructed by introducing multiple triphenylsilanes into carbazole unit. Impressively, DSiD-CzSi demonstrates...

Realizing highly efficient blue photoluminescence of dimethylsilane-aryl (phenylene, diphenylene, fluorenyl) main-chain polymers with σ–π conjugation

“…30,37 The final products with large extent of σ–π conjugations derived from superior charge injection and transport of the main chain exhibit distinguished fluorescence performances. 39,40 The basis of this technology is to introduce aryl groups with excellent fluorescence properties into the –Si–C– backbone via the Grignard reaction and yield an organosilicon polymer with alternating π-conjugated units. Here, we demonstrate that the ingenious integration of aryl and –Si–C– backbones can realize easy film-forming ability, stability of homogeneous organic films, high quantum yields and high intrinsic charge carrier mobility of organosilicon polymers in an easy and economic manner, with a view to various flexible optoelectronic applications (such as blue polymer light emitting diodes, fluorescent sensors, fluorescent probes and blue X-ray imaging) in the near future.…”

Bipolar Arylsilane: Synthesis, Photoelectronic Properties, and High-Performance Deep Blue Organic Light-Emitting Diodes

“…Bipolar molecules have been extensively adopted for use as a host as well as for a dopant in the design of a blue emitter with high performance. − Balanced transport and low injection barriers for carriers can be achieved through the modulation of energy levels of frontier orbitals in bipolar molecules with donor–acceptor (D–A) moieties . Owing to their high triplet energy levels and excellent hole transport ability, carbazole and triphenylamine derivatives have been widely reported as hosts, and bipolar molecules can be established when electron-deficient groups are introduced, such as pyridine, pyrimidine, triazole, oxadiazole, pyrazole, cyano, benzimidazole, phenanthroimidazole, and phosphine oxide. − Nevertheless, a strong interaction between the electron-rich group and electron-deficient group, especially in a π-conjugated D–A system, must be avoided to prevent a charge transfer (CT), which can lead to a low fluorescence quantum efficiency and a sacrifice in the color of pure blue and deep blue luminogens. Therefore, it is truly necessary to carefully design the molecular structure to regulate energy levels, so that the desirable deep blue emission with a high efficiency can be acquired. , …”

Phosphine Sulfide-Based Bipolar Host Materials for Blue Phosphorescent Organic Light-Emitting Diodes

“…Bipolar hosts, generally prepared by combining the donor (D) and acceptor (A) units into a molecular skeleton (i.e., D–A molecules), are capable of achieving a broad recombination zone and balanced charge in the emitting layer (EML), so they are considered one of the most promising types of hosts to realize highly efficient PhOLEDs [ 6 , 7 , 8 ]. Up until the present, the bipolar hosts for green, yellow, and red phosphorescent emitters have made commendable progress [ 9 , 10 , 11 , 12 ], while it is still challenging to develop superior blue hosts because the blue phosphors inherently possess high triplet energy ( E T ) levels [ 13 , 14 , 15 ], thus the E T of the hosts should be accordingly elevated to prevent the reverse energy transfer from the guests back to the hosts and to effectively confine triplet excitons on the guests. However, the non-negligible intramolecular interactions in D–A molecules would produce a low energy charge transfer (CT) state, which brings down the E T levels [ 16 ].…”