Solution-processed multi-resonance organic light-emitting diodes with high efficiency and narrowband emission

With excellent color purity(full-width half maximum(FWHM)<40 nm)and high quantum yield,multiresonance(MR)molecules can harvest both singlet and triplet excitons for highly efficient narrowband organic light-emitting diodes(OLEDs)owing to their thermally activated delayed fluorescence(TADF)nature.However,the highly rigid molecular skeleton with the oppositely positioned bo ron and nitrogen in generating MR effects results in the intrinsic difficulties in the solution-processing of MR-OLEDs.Here,we demonstrate a facile strategy to increase the solubility,enhance the efficiencies and modulate emission color of MR-TADF molecules by extending aromatic rings and introducing tert-butyls into the MR backbone.Two MR-TADF emitters with smaller singlet-triplet splitting energies(ΔE~(ST))and larger oscillator strengths were prepared conveniently,and the solution-processed MR-OLEDs were fabricated for the first time,exhibiting efficient bluish-green electroluminescence with narrow FWHM of 32 nm and external quantum efficiency of 16.3%,which are even comparable to the state-of-the-art performances of the vacuum-evaporated devices.These results prove the feasibility of designing efficient solutionprocessible MR molecules,offering important clues in developing high-performance solution-processed MR-OLEDs with high efficiency and color purity.

Near-Infrared-Excitable Organic Ultralong Phosphorescence through Multiphoton Absorption

Organic ultralong room-temperature phosphorescence(OURTP)with a long-lived triplet excited state up to several seconds has triggered widespread research interests,but most OURTP materials are excited by only ultraviolet(UV)or blue light owing to their unique stabilized triplet-and solid-state emission feature.Here,we demonstrate that near-infrared-(NIR-)excitable OURTP molecules can be rationally designed by implanting intra/intermolecular charge transfer(CT)characteristics into Haggregation to stimulate the efficient nonlinear multiphoton absorption(MPA).The resultant upconverted MPA-OURTP show ultralong lifetimes over 0.42 s and a phosphorescence quantum yield of~37%under both UV and NIR light irradiation.Empowered by the extraordinary MPA-OURTP,novel applications including two-photon bioimaging,visual laser power detection and excitation,and lifetime multiplexing encryption devices were successfully realized.These discoveries illustrate not only a delicate design map for the construction of NIR-excitable OURTP materials but also insightful guidance for exploring OURTP-based nonlinear optoelectronic properties and applications.

Resonance hosts for high efficiency solution-processed blue and white electrophosphorescent devices

The exploration of high-performance solution-processible host materials for blue and white electrophosphorescent devices is a key and fundamental challenge in the ongoing development of organic semiconductors.Herein,two solution-processible resonance host materials with self-adaptive characteristics are delicately designed and constructed.Because of the dynamic tautomerization upon resonance variation,these smart hosts show self-adaptive and selectively enhanced charge carrier flux at high triplet energy levels.Conferred by the resonance molecules,solution-processed blue and white devices exhibit excellent maximum current efficiencies(CEs)of 29.8 and 57.3 cd A−1,and external quantum efficiencies(EQEs)up to 14.5%and 23.5%,respectively.Our works highlight the significant progress of the solution-processed phosphorescent organic light-emitting diodes(PhOLEDs)using resonance host molecules,potentially furnishing a leap forward in constructing advanced organic semiconductors for next-generation optoelectronic devices.

Constructing Donor-Resonance-Donor Molecules for AcceptorFree Bipolar Organic Semiconductors

Organic semiconductors with bipolar transporting character are highly attractive as they offer the possibility to achieve high optoelectronic performance in simple device structures.However,the continual efforts in preparing bipolar materials are focusing on donor-acceptor(D-A)architectures by introducing both electron-donating and electron-withdrawing units into one molecule in static molecular design principles.Here,we report a dynamic approach to construct bipolar materials using only electron-donating carbazoles connected by N-P=X resonance linkages in a donor-resonance-donor(D-r-D)structure.By facilitating the stimuli-responsive resonance variation,these D-r-D molecules exhibit extraordinary bipolar properties by positively charging one donor of carbazole in enantiotropic N^(+)=P-X-canonical forms for electron transport without the involvement of any acceptors.With thus realized efficient and balanced charge transport,blue and deep-blue phosphorescent organic light emitting diodes hosted by these D-r-D molecules show high external quantum efficiencies up to 16.2%and 18.3%in vacuum-deposited and spin-coated devices,respectively.These results via the D-r-D molecular design strategy represent an important concept advance in constructing bipolar organic optoelectronic semiconductors dynamically for high-performance device applications.