以昇陳

Diarylfluorene is a non-planar architecture with two aromatic phenyls connected to a tetrahedral sp³ hybrid carbon, which can be applied to construct organic semiconductors. This overview mainly reports the recent development of diarylfluorene derivatives, including 9,9′-diarylfluorene, heteroatom-containing spirocyclic diarylfluorene, and 4-position substituted 9,9′-diarylfluorene. The synthetic routes, molecular structures, and their diverse applications toward optoelectronic devices are introduced and summarized systematically.

Abstract

Modular production is a convenient strategy that not only realizes the mass production of conjugated materials, but also precisely regulates their photoelectrical property for optoelectronic applications. Diarylfluorene is a functional building block in constructing organic semiconductors arising from its special electronic, spacial, and conformational structure. Because of easy chemical modification, tunable electronic structure, and high photoluminescence quantum yield, diarylfluorene-based conjugated materials have undergone remarkable development in variety of low-cost optoelectronic devices. Herein, the authors present an overview mainly to describe the recent research progresses of diarylfluorene-based molecules, including 9,9′-diarylfluorene, heteroatom-containing spirocyclic diarylfluorene, and 4-position substituted 9,9′-diarylfluorene. The synthetic routes, molecular structures as well as their diverse applications toward optoelectronic devices are introduced and summarized systematically. Finally, the future challenges and development are also discussed in this vital research field.

By incorporating a weak electron donor (DDB) into the near-infrared-II (NIR-II) emissive organic semiconducting polymer (OSP), its NIR-II fluorescence is significantly enhanced. Excited state dynamics investigation elucidate the DDB incorporation-induced suppression of vibrational relaxation as the underlying reason for the fluorescence enhancement, providing an effective molecular guideline to optimize the NIR-II fluorescence performance of OSPs for improved phototheranostics.

Abstract

Exploration of high-efficiency agents for near-infrared-II fluorescence imaging (NIR-II FI) promotes the development of NIR-II FI in life science. Despite the extensive use of organic semiconducting nanomaterials for NIR-II FI, the fluorescence efficiency is barely satisfying, and the molecular guideline to improve the imaging quality has not been clarified yet. This contribution designs self-brightened organic semiconducting polymers (OSPs) for improved NIR-II phototheranostics of cancer. The amplification of NIR-II brightness is realized by incorporating a weak electron-donating unit (5,5′-dibromo-4,4′-didodecyl-2,2′-bithiophene, DDB) into the semiconducting backbone with strong electron donor–acceptor alternated structure, which exhibits 6.3-fold and 25-fold fluorescence enhancement compared with the counterpart OSP at the same optical concentration and mass concentration, respectively. The broadband femtosecond transient absorption spectra experimentally elucidate the DDB doping-induced suppression of vibrational relaxation as the underlying reason for the NIR-II fluorescence amplification. Biocompatible nanoparticles fabricated from the optimal OSP₁₂ exhibit excellent NIR-II phototheranostic performance both in vitro and in vivo. Our research not only reveals the mechanistic insights for fluorescence enhancement of the designed OSPs from the essential view but also highlights an effective molecular methodology to guide the rational design of imaging agents with enhanced NIR-II brightness for improved phototheranostics in living subjects.

An investigation is conducted on ionically mediated mechanical deformation accompanied by memristive switching through simultaneous conductive atomic force microscopy and electrochemical strain microscopy. The correlation between the electrochemical strain and memristive switching associated with applied voltage is presented. This approach provides insight into the ionic behavior that can be extended to other ionic active systems.

Abstract

Ionically mediated phenomena underpin the functioning of various devices, including batteries, solid oxide fuel cells, memristors, and neuromorphic devices. The ionic behavior corresponding to ionically mediated phenomena causes not only variations in the electrical properties but also mechanical deformation, which is crucial for device reliability. However, the interrelation between ionically mediated electrical properties and mechanical deformation has not been elucidated yet. This study investigates ionically mediated mechanical deformation accompanied by memristive switching in a TiO₂ single crystal through simultaneous conductive atomic force microscopy and electrochemical strain microscopy. A comprehensive analysis indicates the existence of a relationship between mechanical deformation and memristive switching based on the ionic behavior. Furthermore, an ionic state variable is used to simplify the interrelation between the electrochemical strain hysteresis and memristive switching associated with applied voltage. This study provides insights on the ionic behavior and can be extended to other systems for the general analysis of the relationship between mechanical deformation and electrical properties.

Two new deep blue TADF emitters, DBA–BFICz and DBA–BTICz are designed while modifying the rigid diindolocarbazole donor by substituting heteroatoms of oxygen and sulphur. Heteroatoms in the donor moiety help to reduce the donor strength, while shifting the emission below 450 nm. Such phenomena support enhancing the spectral overlap with ν-DABNA fluorescent dopant through an effective Förster resonance energy transfer.

Abstract

Simultaneously obtaining high efficiency and deep blue emission in organic light emitting diodes (OLEDs) remains a challenge. To overcome the demands associated with deep blue thermally activated delayed fluorescence (TADF) emitters, two deep blue TADF materials namely, DBA–BFICz and DBA–BTICz, are designed and synthesized by incorporating oxygen-bridged boron (DBA) acceptor with heteroatoms, oxygen and sulphur-based donors, BFICz and BTICz, respectively. Both TADF materials show deep blue photoluminescence emissions below 450 nm by enhancing the optical band gap over 2.8 eV through deeper highest occupied molecular orbital (HOMO) level of heteroatom based donor moieties. At the same time, the photoluminescence quantum yields (PLQYs) of both TADF materials remain over 94%. The TADF device with DBA–BFICz as an emitter exhibits a good external quantum efficiency (EQE) of 33.2%. Since both new TADF materials show deep blue emissions and high efficiencies, hyperfluorescence (HF) OLED devices are fabricated using ν-DABNA as a fluorescence dopant. DBA–BFICz as a TADF sensitized host in HF–OLED reveals an outstanding EQE of 38.8% along with narrow full width at half maximum of 19 nm in the bottom emission pure blue OLEDs. This study provides an approach to develop deep blue TADF emitters for highly efficient OLEDs.

Furan-phenylene co-oligomers commonly show inherent bright luminescence, enhanced molecular rigidity, but only p-type charge transport. Their selective fluorination improves the crystal packing, dramatically enhances the photostability, and provides well-balanced ambipolar charge transport. As a result, the optimally fluorinated oligomer demonstrates efficient electroluminescence in ambipolar single-layer organic light-emitting transistors.

Abstract

Linearly conjugated oligomers attract ever-growing attention as promising systems for organic optoelectronics because of their inherent lucky combination of high charge mobility and bright luminescence. Among them, furan-phenylene co-oligomers (FPCOs) are distinguished by outstanding solubility, very bright luminescence, and good hole-transport properties; however, furan-containing organic semiconductors generally lack electron transport, which makes it impossible to utilize them in efficient light-emitting electronic devices, specifically, ambipolar light-emitting transistors. In this work, 1,4-bis(5-phenylfuran-2-yl)benzene (FP5) derivatives are synthesized with the fully/partially fluorinated central and edge phenyl rings. It is shown that the selective fluorination of FPCOs lowers the energies of frontier molecular orbitals, maintaining the bandgap, solubility, and bright luminescence, dramatically improves the photostability, tunes the π-π stacked packing, and allows the first realization of electron transport in FPCOs. It is found that selectively fluorinated 2,2′-(2,3,5,6-tetrafluoro-1,4-phenylene)bis[5-(3,5-difluorophenyl)furan] demonstrates well-balanced ambipolar charge transport and efficient electroluminescence in an organic light-emitting transistor (OLET) with external quantum and luminous efficiencies as high as 0.63% and 5 cdA⁻¹, respectively, which are among the best reported for OLETs. The findings show that “smart” fluorination is a powerful tool to fine-tune the stability and performance of linearly conjugated small molecules for organic optoelectronics.

Nature Photonics, Published online: 27 August 2021; doi:10.1038/s41566-021-00855-2

A universal method is developed to activate near-infrared-excited multicolor afterglow of carbon dots-based RTA materials (CDAMs) through radiative energy transfer from NaYF₄:Yb,Tm upconversion materials (UMs). The resulting UM/CDAMs demonstrate bright and persistent afterglow from blue to orange under NIR CW laser excitation at 980 nm.

Abstract

Room-temperature afterglow (RTA) materials with long lifetime have shown tremendous application prospects in many fields. However, there is no general design strategy to construct near-infrared (NIR)-excited multicolor RTA materials. Herein, we report a universal approach based on the efficient radiative energy transfer that supports the reabsorption from upconversion materials (UMs) to carbon dots-based RTA materials (CDAMs). Thus, the afterglow emission (blue, cyan, green, and orange) of various CDAMs can be activated by UMs under the NIR continuous-wave laser excitation. The efficient radiative energy transfer ensured the persistent multicolor afterglow up to 7 s, 6 s, 5 s, and 0.5 s by naked eyes, respectively. Given the unusual afterglow properties, we demonstrated preliminary applications in fingerprint recognition and information security. This work provides a new avenue for the activation of NIR-excited afterglow in CDAMs and will greatly expand the applications of RTA materials.

Thermally activated delayed fluorescent molecules with ortho-linked multiple donor–acceptor motifs are constructed to realize both fast radiative decay and reverse intersystem crossing, thanks to the enhanced multiple-charge transfers and near-degenerate excited states. The optimized device exhibits narrow-band green electroluminescence with a EQE_max/CIE _y of 31.6 %/0.69, being the purest green bottom-emitting organic light-emitting diode.

Abstract

Thermally activated delayed fluorescence (TADF) materials with through-space charge transfers (CT) have attracted particularly interest recently. However, the slow reverse intersystem crossing (RISC) and radiative decay always limit their electroluminescence performances. Herein, TADF molecules with ortho-linked multiple donors-acceptor (ortho-D_n-A) motif are developed to create near-degenerate excited states for the reinforcement of spin-orbit coupling. The incorporation of both through-bond and through-space CT enlarges oscillator strength. The optimal ortho-D₃-A compound exhibits a photoluminescence quantum yield of ca. 100 %, a high RISC rate of 2.57×10⁶ s⁻¹ and a high radiative decay rate of 1.00×10⁷ s⁻¹ simultaneously. With this compound as the sensitizer, a TADF-sensitized-fluorescent organic light-emitting diode shows a maximum external quantum efficiency of 31.6 % with an ultrapure green Commission Internationale de L'Eclairage y coordinate value of 0.69.

A simple and versatile design strategy enabled wide-range color tuning of narrowband emissions in organoboron luminogenic molecules. The introduction of imine and amine moieties into a boron-embedded 1,3-bis(carbazol-9-yl)benzene skeleton (see structures) caused hypsochromic and bathochromic emission band shifts, respectively, thereby leading to deep-blue to yellow narrowband thermally activated delayed fluorescence with excellent color purity.

Abstract

Establishing a simple and versatile design strategy to finely modulate emission colors while retaining high luminescence efficiency and color purity remains an appealing yet challenging task for the development of multi-resonance-induced thermally activated delayed fluorescence (MR-TADF) materials. Herein, we demonstrate that the strategic introduction of electron-withdrawing imine and electron-donating amine moieties into a versatile boron-embedded 1,3-bis(carbazol-9-yl)benzene skeleton enables systematic hypsochromic and bathochromic shifts of narrowband emissions, respectively. By this method, effective electroluminescence color tuning was accomplished over a wide visible range from deep-blue to yellow (461–571 nm), using the same MR molecular system, without compromising very narrow spectral features. Deep-blue to yellow organic light-emitting diodes with maximum external quantum efficiencies as high as 19.0–29.2 % and superb color purity could be produced with this family of color-tunable MR-TADF emitters.

A robust hole transporting layer based on cobalt(II) acetate was developed by aqueous solution processing technology, low temperature thermal annealing and UV-ozone treatment, which enabled a record high-power conversion efficiency of 18.77 % of binary blend organic solar cells.

Abstract

A robust hole transporting layer (HTL), using the cost-effective Cobalt(II) acetate tetrahydrate (Co(OAc)₂⋅4 H₂O) as the precursor, was simply processed from its aqueous solution followed by thermal annealing (TA) and UV-ozone (UVO) treatments. The TA treatment induced the loss of crystal water followed by oxidization of Co(OAc)₂⋅4 H₂O precursor, which increased the work function. However, TA treatment differently realize a high work function and ideal morphology for charge extraction. The resulting problems could be circumvented easily by additional UVO treatment, which also enhanced the conductivity and lowered the resistance for charge transport. The optimal condition was found to be a low temperature TA (150 °C) followed by simple UVO, where the crystal water in Co(OAc)₂⋅4 H₂O was removed fully and the HTL surface was anchored by substantial hydroxy groups. Using PM6 as the polymer donor and L8-BO as the electron acceptor, a record high PCE of 18.77 % of the binary blend OSCs was achieved, higher than the common PEDOT:PSS-based solar cell devices (18.02 %).

Circularly polarized luminescence (CPL) transmission is a critical challenge in chiroptical research but there are two questions on CPL transmission. How to transfer CPL within intermolecular systems? And can achiral emitters emit CPL? We find the CPL transmission is critically dependent on the resonance transfer, which was attributed to unique circularly polarized fluorescence resonance energy transfer (C-FRET).

Abstract

The occurrence and transmission of chirality is a fascinating characteristic of nature. However, the intermolecular transmission efficiency of circularly polarized luminescence (CPL) remains challenging due to poor through-space energy transfer. We report a unique CPL transmission from inducing the achiral acceptor to emit CPL within a specific liquid crystal (LC)-based intermolecular system through a circularly polarized fluorescence resonance energy transfer (C-FRET), wherein the luminescent cholesteric LC is employed as the chirality donor, and rationally designed achiral long-wavelength aggregation-induced emission (AIE) fluorophore acts as the well-assembled acceptor. In contrast to photon-release-and-absorption, the chirality transmission channel of C-FRET is highly dependent upon the energy resonance in the highly intrinsic chiral assembly of cholesteric LC, as verified by deliberately separating the achiral acceptor from the chiral donor to keep it far beyond the resonance distance. This C-FRET mode provides a de novo strategy concept for high-level information processing for applications such as high-density data storage, combinatorial logic calculation, and multilevel data encryption and decryption.

A triple-jump photodynamic theranostics protocol is explored for high-efficacy cancer treatment, by establishing an intelligent glutathione-depleting and NIR-regulated theranostic nanoplatform comprising a MnO₂ nanoshell, upconversion nanoparticles, and aggregation-induced emission-active Type-I photosensitizers.

Abstract

The development of multifunctional nanoplatforms has been recognized as a promising strategy for potent photodynamic theranostics. Aggregation-induced emission (AIE) photosensitizers undergoing Type-I reactive oxygen species (ROS) generation pathway appear as potential candidates due to their capability of hypoxia-tolerance, efficient ROS production, and fluorescence imaging navigation. To further improve their performance, a facile and universal method of constructing a type of glutathione (GSH)-depleting and near-infrared (NIR)-regulated nanoplatform for dual-modal imaging-guided photodynamic therapy (PDT) is presented. The nanoplatforms are obtained through the coprecipitation process involving upconversion nanoparticles (UCNPs) and AIE-active photosensitizers, followed by in situ generation of MnO₂ as the outer shell. The introduction of UCNPs actualizes the NIR-activation of AIE-active photosensitizers to produce ·OH as a Type-I ROS. Intracellular upregulated GSH-responsive decomposition of the MnO₂ shell to Mn²⁺ realizes GSH-depletion, which is a distinctive approach for elevating intracellular ·OH. Meanwhile, the generated Mn²⁺ can implement T ₁-weighted magnetic resonance imaging (MRI) in specific tumor sites, and mediate the conversion of intracellular H₂O₂ to ·OH. These outputs reveal a triple-jump ·OH production, and this approach brings about distinguished performance in FLI-MRI-guided PDT with high-efficacy, which presents great potential for future clinical translations.

Organic solar cells that employ donor:acceptor blends with near-zero driving force for charge transfer are becoming prevalent because of their superior performance. In this work, the factors affecting charge transfer and subsequent dissociation of the charge-transfer state are experimentally and theoretically analyzed. Short excited-state lifetime and hybridization open up new recombination channels with detrimental effects on free-charge generation.

Abstract

A blend of a low-optical-gap diketopyrrolopyrrole polymer and a fullerene derivative, with near-zero driving force for electron transfer, is investigated. Using femtosecond transient absorption and electroabsorption spectroscopy, the charge transfer (CT) and recombination dynamics as well as the early-time transport are quantified. Electron transfer is ultrafast, consistent with a Marcus–Levich–Jortner description. However, significant charge recombination and unusually short excited (S₁) and CT state lifetimes (≈14 ps) are observed. At low S₁–CT offset, a short S₁ lifetime mediates charge recombination because: i) back-transfer from the CT to the S₁ state followed by S₁ recombination occurs and ii) additional S₁–CT hybridization decreases the CT lifetime. Both effects are confirmed by density functional theory calculations. In addition, relatively slow (tens of picoseconds) dissociation of charges from the CT state is observed, due to low local charge mobility. Simulations using a four-state kinetic model entailing the effects of energetic disorder reveal that the free charge yield can be increased from the observed 12% to 60% by increasing the S₁ and CT lifetimes to 150 ps. Alternatively, decreasing the interfacial CT state disorder while increasing bulk disorder of free charges enhances the yield to 65% in spite of the short lifetimes.

Through regulating the noncovalent interactions between organic semiconductor molecules (|ECT, DgpC-TCNB = −18.35 kcal mol⁻¹| > |ECT, DgpC-TFP = −13.45 kcal mol⁻¹| > |Eπ–π, DgpC = −6.81 kcal mol⁻¹|), a hierarchical self-assembly approach of horizontal epitaxial-growth is demonstrated for the precise synthesis of organic core/double-shell microwires with radial red–green–blue (RGB) substructures for miniaturized white-light sources (CIE [0.34, 0.36]).

Abstract

White-light-emissive organic micro/nanostructures hold exotic potential applications in full-color displays, on-chip wavelength-division multiplexing, and backlights of portable display devices, but are rarely realized in organic core/shell heterostructures. Herein, through regulating the noncovalent interactions between organic semiconductor molecules, a hierarchical self-assembly approach of horizontal epitaxial-growth is demonstrated for the fine synthesis of organic core/mono-shell microwires with multicolor emission (red–green, red–blue, and green–blue) and especially organic core/double-shell microwires with radial red–green–blue (RGB) emission, whose components are dibenzo[g,p]chrysene (DgpC)-based charge-transfer (CT) complexes. In fact, the desired lattice mismatching (≈2%) and the excellent structure compatibility of these CT complexes facilitate the epitaxial-growth process for the facile synthesis of organic core/shell microwires. With the RGB-emissive substructures, these core/double-shell organic microwires are microscale white-light sources (CIE [0.34, 0.36]). Besides, the white-emissive core/double-shell microwires demonstrate the fascinating full-spectrum light transportation from 400 to 700 nm. This work indeed opens up a novel avenue for the accurate construction of organic core/shell heterostructures, which provides an attractive platform for the organic integrated optoelectronics.

An extremely efficient ion-exchange doping process for conjugated polymers which enables conductivities exceeding 1000 S cm⁻¹ is demonstrated. Factors which affect ion exchange, such as electrolyte concentration, doping solvent, and film crystallinity are discussed. When exchange is efficient there is a direct correspondence between ion exchange electrochemical doping, which is used to reveal the detrimental impact of off-target oxidation reactions.

Abstract

Molecular doping—the use of redox-active small molecules as dopants for organic semiconductors—has seen a surge in research interest driven by emerging applications in sensing, bioelectronics, and thermoelectrics. However, molecular doping carries with it several intrinsic problems stemming directly from the redox-active character of these materials. A recent breakthrough was a doping technique based on ion-exchange, which separates the redox and charge compensation steps of the doping process. Here, the equilibrium and kinetics of ion exchange doping in a model system, poly(2,5-bis(3-alkylthiophen-2-yl)thieno(3,2-b)thiophene) (PBTTT) doped with FeCl₃ and an ionic liquid, is studied, reaching conductivities in excess of 1000 S cm⁻¹ and ion exchange efficiencies above 99%. Several factors that enable such high performance, including the choice of acetonitrile as the doping solvent, which largely eliminates electrolyte association effects and dramatically increases the doping strength of FeCl₃, are demonstrated. In this high ion exchange efficiency regime, a simple connection between electrochemical doping and ion exchange is illustrated, and it is shown that the performance and stability of highly doped PBTTT is ultimately limited by intrinsically poor stability at high redox potential.

A novel organic upconversion device (UCD) based on interfacial exciplexes, which shows high conversion efficiency near 13%, low turn-on voltage (V _on) down to 1.56 V, high imaging linear dynamic range (I-LDR) over 80 dB, and high luminance on/off ratio of up to 85 000, is fabricated for high-performance near-infrared (NIR) light detection and noninvasive direct imaging.

Abstract

Infrared upconversion devices (UCDs) enable low-cost visualization of infrared optical signals without utilizing a readout circuit, which is of great significance for biological recognition and noninvasive dynamic monitoring. However, UCDs suffer from inferior photon to photon (p–p) efficiency and high turn-on voltage (V _on) for upconversion operation, hindering a further expansion in highly resolved infrared imaging. Herein, an efficient organic UCD integrating an interfacial exciplex emitter and a well-designed near-infrared (NIR) detector reveals a high efficiency up to 12.92% and a low V _on down to 1.56 V. The low V _on gives the capacity for detecting weak NIR light down to 3.2 µW cm^–2, significantly expanding the detection power scale of UCDs. Thus, the imaging linear dynamic range (I-LDR) is highly bias-tunable, ranging from 13.23 to 84.4 dB. The high I-LDR enables highly resolved and strong-penetration bioimaging especially for thick biological sections, indicating great potential in noninvasive defect and pathological detection.