Ultrafast photoexcitation dynamics behavior of hydrogen-bonded polyfluorenol

Exciton behavior is crucial to the exploitation of light-emitting conjugated polymer(LCPs)for optoelectronic devices.Singlet excitons are easily trapped by the intrinsically defect structures.Herein,we set a polyfluorenol(PPFOH)as an example to systematically investigate its photophysical behavior to check the role of defect structures in LCPs.According to time-resolved photoluminescence analysis,the feature emission peaks from individual chain of PPFOH in diluted DMF solution is effectively avoided the influence of fluorenone formation,but the residual green-band emission at 550nm is easily observed in the PL spectra of PPFOH dilute toluene solution obtained delay 1.5 ns,confirmed the formation of“guest”physical aggregation-induced defect structure.Remarkably,efficient and ultrafast energy transfer from individual chain to defect structure is observed in PPFOH films.Interestingly,the efficient energy transfer happened for the film obtained from DMF solution(200 ps)than those of toluene ones(600 ps).Meanwhile,compared to relatively stable green-band emission in PPFOH film from toluene solution,red-shifted emission peak(11 nm)of PPFOH film from DMF solutions exposed to saturated DNT vapor also confirmed their different aggregation-induced green-band emission.Therefore,this aggregation defect structures are influenced on the photophysical property of LCPs in solid states.

Promoting near-infrared II fluorescence efficiency by blocking long-range energy migration

Generally,long wavelength absorbed near-infrared II(NIR-II)dyes have a low fluorescence efficiency in aggregate states for aggregate-caused quenching effect,simultaneously enhancing efficiency and extending absorption is a challenging issue for NIR-II dyes.Here,three benzo[1,2-c:4,5-c’]bis[1,2,5]thiadiazole(BBT)derivatives(TPA-BBT,FT-BBT,and BTBT-BBT)are used to clarify fluorescence quenching mechanisms.When the BBT derivatives are doped into a small molecule matrix,they show quite different fluorescence behaviors.Structuredistorted TPA-BBT displays fluorescence quenching originating from short-range exchange interaction,while FT-BBT and BTBT-BBT with a co-planar-conjugated backbone exhibit concentration-dependent quenching processes,namely changing from long-range dipole-dipole interaction to exchange interaction,which could be majorly ascribed to large spectral overlap between absorption and emission.By precisely tuning doping concentration,both FT-BBT and BTBT-BBT nanoparticles(NPs)present the optimal NIR-II fluorescence brightness at∼2.5 wt%doping concentration.The doped NPs have good biocompatibility and could be served as fluorescence contrast agents for vascular imaging with a high resolution under 980-nm laser excitation.Those paradigms evidence that molecular doping can promote fluorescence efficiency of long wavelength-absorbed NIR-II fluorophores via suppressing long-range energy migration.

Hierarchical structures,surface morphology and mechanical elasticity of lamellar crystals dominated by halogen effects

To understand the deformation mechanism of molecular crystals under mechanical forces will accelerate the molecular design and preparation of deformable crystals.Herein,the relationship between structural halogenation and molecular-level stacking,micro/nanoscale surface morphology,and macroscopic mechanical properties are investigated.Elastic crystals of halo-pyrimidinyl carbazoles(CzM-Cl,CzM-Br and CzM-I)with lamellar structure and brittle crystal(CzM-F)were quantitatively analyzed by crystal energy framework(CEF)providing the inter/intralayer interaction energy(Inter/Intra-IE).It is revealed that the elastic crystals bend under external force as a result from stronger Intra-IE to prevent cleavage and weaker Inter-IE for the short-range movement of molecules on the slip plane.This research will provide an insight for the molecular design of flexible crystals and facilitate the development of next-generation smart crystal materials.

Photoexcitation dynamics and energy engineering in supramolecular doping of organic conjugated molecules

Doping and blending strategies are crucial means to precisely control the excited states and energy level in conjugated molecular systems.However,effective models and platforms are rarely proposed to systematically explore the effects of the formation of trapped doped centers on heterogeneous structures,energy level and ultrafast photophysical process.Herein,for deeply understanding the impact of molecular doping in film energy levels and photoexcitation dynamics,we set a supramolecular N-B coordination composed by the conjugated molecules of pyridine functionalized diarylfluorene(host material),named as ODPF-Phpy and ODPF-(Phpy)2,and the molecule of tris(perfluorophenyl)borane(BCF)(guest material).The generation of the molecular-level coordination bond increased the binding energy of N atoms and tuned the band-gap,leading to a new fluorescent emission center with longer excitation wavelength and emission wavelength.The intermolecular Forster resonance energy transfer(FRET)in blending flms make it present inconsistent fluorescent behaviors compared to that in solution.The charge transfer(CT)state of N-B coordinated compounds and the changed dielectric constant of blending films resulted in a large PL spectra red-shift with the increased dopant ratio,causing a wide-tunable fluorescent color.The excited state behaviors of two compounds in blending system was further investigated by the transient absorption(TA)spectroscopy.Finally,we found supramolecular coordination blending can effectively improve the films'photoluminescence quantum yield(PLQY)and conductivity.We believe this exploration in the internal coordination mechanisms would deepen the insights about doped semiconductors and is helpful in developing novel high-efficient fluorescent systems.

In Situ Super-Hindrance-Triggered Multilayer Cracks for Random Lasing inπ-Functional Nanopolymer Films

In situ self-assembly of semiconducting emitters into multilayer cracks is a significant solution-processing method to fabricate organic high-Q lasers.However,it is still difficult to realize from conventional conjugated polymers.Herein,we create the molecular super-hindrance-etching technology,based on theπ-functional nanopolymer PG-Cz,to modulate multilayer cracks applied in organic single-component random lasers.Massive interface cracks are formed by promoting interchain disentanglement with the super-steric hindrance effect ofπ-interrupted main chains,and multilayer morphologies with photonic-crystal-like ordering are also generated simultaneously during the drop-casting method.Meanwhile,the enhancement of quantum yields on micrometer-thick films(Φ=40%to 50%)ensures high-efficient and ultrastable deep-blue emission.Furthermore,a deep-blue random lasing is achieved with narrow linewidths~0.08 nm and high-quality factors Q≈5,500 to 6,200.These findings will offer promising pathways of organicπ-nanopolymers for the simplification of solution processes applied in lasing devices and wearable photonics.

可溶液加工还原氧化石墨烯:制备、功能化、自组装及在智能信息器件中的应用

石墨烯作为一种苯结构无限延伸的纳米与介观分子,表现出多层次迥异的物理与化学特性.本文从机械剥离法制备的石墨烯的奇特物理性质追溯氧化石墨烯(GO)相关化学反应的开展,再到其共价/非共价功能化及应用,用分级化学的视角梳理了该领域的化学进展.重点论述了化学方法制备的氧化石墨烯及还原氧化石墨烯(rGO)在溶液分散态下的功能化方法和自组装结构.针对环境友好的可溶液加工GO/rGO工艺面临的问题,总结了纳米片分散性、片间相互作用及其薄膜工艺的相关进展,为研究其墨水配方、成膜工艺和薄膜微结构的控制提供了指导.最后在总结rGO薄膜材料相关研究进展的基础上,介绍了其在智能信息器件中的应用,并对存在的挑战性问题和未来研究方向提出自己的观点.

热活化延迟荧光蓝光小分子取代基效应的研究进展

近年来,作为第三代有机发光二极管(organic light-emitting diodes,OLED)发光材料的热活化延迟荧光(thermally activated delayed fluorescence,TADF)材料受到了学术界和产业界的广泛关注.TADF分子由于其单线态与三线态之间的能级差较小,三线态激子可以被环境热活化而通过反系间窜越上转换至单线态,理论上可实现100%的激子利用率,从而使得OLED器件外量子效率显著提高.TADF材料被认为是突破高效稳定有机电致蓝光发射瓶颈的潜在解决方案.一般,TADF分子为含有电子给体(donor,D)和电子受体(acceptor,A)的纯有机推拉电子体系.通过改变给体单元和受体单元的结构、数量和取代基及其位置可以有效调节TADF分子的单线态-三线态能级差、前线轨道分布、聚集态结构、电致发光颜色及其性能.同时取代基在调控给、受体单元的推拉电子能力及TADF材料的分子构型、聚集态结构和稳定性等物化特性方面扮演着非常重要的角色.本综述分别对D-A型和多重共振型TADF蓝光分子的取代基效应进行了综述,以期为高效稳定的蓝光TADF分子的设计合成提供有效借鉴.

基于芴醇基傅克反应制备复杂二芳基芴类半导体

芴醇的傅克反应制备不同结构的复杂二芳基芴(complex diarylfluorenes,CDAFs)赋予空间位阻功能化半导体新的机遇.本文从芴醇基傅克反应的特征、CDAFs结构及其在有机塑料电子领域的应用3个层面进行了综述.首先,概述了位阻型半导体在有机塑料电子的重要地位,追溯傅克反应历史,梳理芴醇基傅克反应特征与优势及其反应规律.然后,介绍了纳米位阻、多位阻、聚合物位阻以及封端型半导体等各类CDAFs结构.最后,总结了CDAFs在有机发光二极管、有机激光、有机太阳能电池、有机光电存储和有机分子与纳米器件中的应用,并展望了未来的"格芴智能"发展方向.

Toward Eco-friendly Green Organic Semiconductors： Recent Advances in Spiro[fluorene-9,9＇-xanthene] （SFX）-Based Optoelectronic Materials and Devices

Green organic semiconductors （GOS） have the four-element features, including biomass as stuffs, synthesis with the pot, atom and step economic （PASE） route, eco-friendly fabrication processes in aqueous phase, and recy- clable devices, capturing the trend of organic electronics in the future. Herein, we reviewed the efforts that have been made on GOS by our group. We first made a brief introduction of organic （opto）electronics, followed by the design strategies of GOSs based on spirofluorenes. Concretely, we described the discovery of one-pot protocol to spirofluorenres and a pot-atom-step economic （PASE） platform of spiro[fluorene-9,9＇-xanthene] （SFX） for the mo- lecular design of organic semiconductors, as well as a state-of-the-art nanocrystalline films with eco-friendly pro- cedures. Then, we highlighted the progress on SFX-based organic semiconductors in the organic light-emitting di- ode （OLED） field. Finally, we conducted a summary on SFXs in OLED and an outlook on green semiconductors starting from biomass, via one-pot to spirofluorenes, to water-phase devices.

Carbazole-endcapped Spiro[fluorene-9,9＇-xanthene] with Large Steric Hindrance as Hole-transporting Host for Heavily-doped and High Performance OLEDs

In this work, we designed and synthesized a novel spirocyclic compound functionalized spiro[fluorene-9,9＇- xanthene] with carbazole group （2-carbazolyl-spiro[fluorene-9,9＇-xanthene], SFX-Cz） via Friedel-Crafts and Ullmann reaction, which is expected to own high thermal and morphological stability, and good carrier injection/ transporting properties due to the excellent hole transporting characteristics of carbazole and cruciform structure of spiro[fluorene-9,9＇-xanthene]. The carbazole end-capped spiro[fluorene-9,9＇-xanthene] SFX-Cz based PhOLEDs with Flrpic as phosphor emitter have been researched by varying dopant concentration, which exhibit the maximum EQEs of 8.9%, 7.4%, 9.1%, and 4.7% with the doping increasing from 10% to 50%. The higher performance PhOLEDs are independent on concentration variation from 10% to 30%, which suggests the bulky steric hindrance of SFX-Cz might be a potential canditate for high performance and inexpensive device with simplified process.

Cross-Scale Synthesis of Organic High-k Semiconductors Based on Spiro-Gridized Nanopolymers

High dielectric constants in organic semiconductors have been identified as a central challenge for the improvement in not only piexoelectric,preolecric,and freeltric efcts but also photoclecric conversion eficiency in OPVs,carrier mobility in OFETS,and charge density in charge-trapping memories.Herein,we report an ultralong persistence length(≈41 nm)efet of spiro-fused organic nanopolymers on dielectric properties,together with excitonic and charge carrier behaviors.The state-of-the-art nanopolymers,namely,nanopolyspirogrids(NPSGs),are synthesized via the simple crossscale Friedel-Crafts polygridlization of AjB-type nanomonomers.The high dielectric constant(k=8.43)of NPSG is firstly achieved by locking spiro-polygridization efect that results in the enhancement of dipole polarization.When doping into a polystyrene-based dielectric layer,such a high-k feature of NPSG increases the feld-ffct carrier mobility from 0.20 to 0.90cm^(2)Vl s'in pentacene OFET devices.Meanwhile,amorphous NPSG film exhibits an ultralow energy disorder(<50 meV)for an exellent zero-field hole mobility of 3.94×10^(-1)cm^(2)V^(-1)s^(-1).surpassing most of the amorphousπconjugated polymers Onganic nanopolymers with high dielectric constants open a new way to break through the bottleneck of eficiency and multifunctionality in the blueprint of the fourth generation semiconductors.

Nanogridarene:A Rising Nanomolecular Integration Platform of Organic Intelligence

In the background of organic electronics,nanogridarenes with the criteria of well-defined edge and extendable vertexes were discovered toward chemical intellibots in 2014.Herein,Friedel-Crafts Gridization(FCG)as the molecular installing technology(MIT)will be highlighted to synthesize various monogrids,multigrids and polygrids that would be potential cornerstone of covalent window,molecular integration and circuit as well as organic robots.

Interface engineering of tungsten carbide/phosphide heterostructures anchored on N,P-codoped carbon for high-efficiency hydrogen evolution reaction

The development of inexpensive and efficient Pt-free electrocatalysts for the hydrogen evolution reaction(HER)is greatly crucial for water electrolysis.Tungsten carbide(WC)exhibiting a Pt-like electronic structure represents an attractive alternative,although its overall performance is limited by the strong W-H bond that impedes hydrogen desorption.Here,we employed an in-situ interface engineering strategy to construct high-performance and cost effective electrocatalysts comprising WC/tungsten phosphide(WP)heterostructures that were anchored on N,P-codoped carbon(WC/WP@NPC)via a one-step pyrolysis of a melamine polyphosphate/WO_(3) hybrid in an inert atmosphere.Owing to the crystal structure compatibility and electron-rich property of WP,it optimizes the electronic structure and hydrogen adsorption configuration of WC,thus significantly weakening the W-H bond with a thermoneutral Gibbs free energy of hydrogen adsorption(ΔG_(H^(*)))of−0.05 eV.Additionally,NPC ensures fast electron transport and structural stability of the WC/WP@NPC ternary architecture.These synergistically lead to outstanding HER performances of the catalyst in acidic and alkaline media.Our finding offers a new strategy for designing Pt-alternative electrocatalysts with outstanding electrochemical performances for high-efficiency water splitting and other applications.

Unveiling the Effects of Interchain Hydrogen Bonds on Solution Gelation and Mechanical Properties of Diarylfluorene-Based Semiconductor Polymers

The intrinsically rigid and limited strain of most conjugated polymers has encouraged us to optimize the extensible properties of conjugated polymers.Herein,learning from the hydrogen bonds in glucose,which were facilitated to the toughness enhancement of cellulose,we introduced interchain hydrogen bonds to polydiarylfluorene by amide-containing side chains.Through tuning the copolymerization ratio,we systematically investigated their influence on the hierarchical condensed structures,rheology behavior,tensile performances,and optoelectronic properties of conjugated polymers.Compared to the reference copolymers with a low ratio of amide units,copolymers with 30%and 40%amide units present a feature of the shearthinning process that resembled the non-Newtonian fluid,which was enabled by the interchain dynamic hydrogen bonds.Besides,we developed a practical and universal method for measuring the intrinsic mechanical properties of conjugated polymers.We demonstrated the significant impact of hydrogen bonds in solution gelation,material crystallization,and thin film stretchability.Impressively,the breaking elongation for P4 was even up to~30%,which confirmed the partially enhanced film ductility and toughness due to the increased amide groups.Furthermore,polymer light-emitting devices(PLEDs)based on these copolymers presented comparable performances and stable electroluminescence(EL).Thin films of these copolymers also exhibited random laser emission with the threshold as low as 0.52μJ/cm^(2),suggesting the wide prospective application in the field of flexible optoelectronic devices.

Enhancement of morphological and emission stability of deep-blue small molecular emitter via a universal side-chain coupling strategy for optoelectronic device

Film morphology of emissive layers is crucial to the performance and stability of solution-processable organic light-emitting diodes(OLEDs). Compared to the interpenetration of conjugated polymer chain,small molecular emitter with a flexible side chain always presents easily aggregation upon external treatment, and caused π-electronic coupling, which is undesirable for the efficiency and stability of deep-blue OLEDs. Herein, we proposed a side-chain coupling strategy to enhance the film morphological an emission stability of solution-processable small molecular deep-blue emitter. In contrary to “parent” MC8 TPA,the crosslinkable styryl and vinyl units were introduced as ended unit at the side-chain of Cm TPA and OEYTPA. Interestingly, Cm TPA and OEYTPA films present a relatively stable morphology and uniform deep-blue emission after thermal annealing(160 ℃) in the atmosphere, different to the discontinuous MC8 TPA annealed film. Besides, compared to the Cm TPA and OEYTPA ones, serious polaron formation in the MC8 TPA annealed film also negative to the deep-blue emission, according to transient absorption analysis. Therefore, both Cm TPA and OEYTPA annealed film obtained at 140 ℃ present an excellent deep-blue ASE behavior with a 445 nm, but absence for MC8 TPA ones, associated with the disruption of annealed films. Finally, enhancement of device performance based on Cm TPA and OEYTPA film(~40%)after thermal annealing with a similar performance curves also confirmed the assumption above. Therefore, these results also supported the effectiveness of our side-chain coupling strategy for optoelectronic applications.

Alkyl-chain branched effect on the aggregation and photophysical behavior of polydiarylfluorenes toward stable deep-blue electroluminescence and efficient amplified spontaneous emission

The control of the condensed superstructure of light-emitting conjugated polymers(LCPs)is a crucial factor to obtain high performance and stable organic optoelectronic devices.Side-chain engineering strategy is an effective platform to tune inter chain aggregation and photophysical behaviour of LCPs.Herein,we systematically investigated the alkyl-chain branched effecton the conformational transition and photophysical behaviour of polydiarylfluorenes toward efficient blue optoelectronic devices.The branched side chain will improve materials solubility to inhibit interchain aggregation in solution according to DLS and optical analysis,which is useful to obtain high quality film.Therefore,our branched PEODPF,POYDPF pristine film present high luminance efficiency of 36.1%and 39.6%,enhanced about 20%relative to that of PODPF.Compared to the liner-type sides'chain,these branched chains also suppress chain planarization and improve film morphological stability effectively.Interestingly,the branched polymer also had excellent stable amplified spontaneous emission(ASE)behaviour with low threshold(4.72μJ/cm2)and a center peak of 465 nm,even thermal annealing at 220℃in the air atmosphere.Therefore,side-chain branched strategy for LCPs is an effective means to control interchain aggregation,film morphology and photophysical property of LCPs.

Self-assembly into Polymorphic 2D Nanosheets with Crystallization-Induced Emission Enhancement

Organic micro/nanocrystals with polymorphic tailorability and perfect platform to modulate decode the complex relationship among molecular structures,supramolecular/noncovalent interactions,aggregates and exciton behaviors.Herein,we precisely tune the polymorphic two-dimensional organic nanosheets(2DONs)of cyano-spirocyclic aromatic hydrocarbon(2'-CN-SFX),where the crystal growth processes are dominated by precursor concentration.The low concentration(ca.2 mmol/L)affords the rhombus-like nanosheets with monoclinic P21/c space group,in which molecules adopt antiparallel and slipped stacking mode.In contrast,the high concentration(ca.4 mmol/L)favors herringbone-like molecular packing pattern and then generates shuttle-like nanosheets with monoclinic C2/c space group.Both above polymorphic nanosheets exhibit unprecedented crystallization-induced emission en-hancement(CIEE)feature that increases the photoluminescence quantum yields(PLQYs)from 16%in solution,21%in amorphous film to 37%-39%in crystalline states.This result will offer promising opportunities for nanophotonics and organic intelligent semi-conductors.

Novel Porphyrin-Containing Polymer Based Memristor for Synaptic Plasticity Simulation

The porphyrin-based copolymer PZnTPP-SFX is designed and synthesized by alternating porphyrin and spiro[fluorene-9,9'-xanthene]via Suzuki copolymerization.A simple memristor structure of ITO/ZnTPP-SFX/AlOx/Al was fabricated by spin-coating process.The conventional synaptic plasticity is emulated using the single memristor including nonlinear transmission characteristics,spike-timing dependent plasticity and spike-rate dependent plasticity.New spike-voltage dependent plasticity is also found in the memristor which can selectively perform potentiation and depression behaviors at a unipolar voltage.Compared with the device performance of uncoordinated metalloporphyrin polymer,it was found that oxygen vacancies diffuse and migrate into PZnTPP-SFX layer with the assist of coordination metal.This study suggests that porphyrin-based polymers have great promise for synaptic simulation of artificial neural network.

Universal 4-qualifiable fluorene-based building blocks for potential optoelectronic applications

In the design of conjugated molecules,modular production enables materials to easily realize structure modification and precisely tune their photoelectrical property.Construction of a novel and universal building block is crucial to design and manufacture high performance and stable conjugated molecules for optoelectronic application.Herein,we originally demonstrated a universal 4-qualifiable fluorene-based building block,which is a fundamental molecular segment to functionalize and obtain novel conjugated materials.Compared to the traditional modification at 9-site,additional 4-position functionalization provided an exciting blueprint to not only tune electronic structure and excited state via p-n molecular design engineering and space charge-transfer strategy,but also allow for optimizing intermolecular arrangement and obtaining solution-processing ability.The introduction of the 4-site substituent in fluorene based semiconductors may endow materials with unique properties.Finally,we successfully prepared two stable deep-blue light-emitting conjugated polymer,PODOPF and PODOF,by utilizing the 4-substituent fluorene based building block.It is believable that the performance,stability and processibility of reported outstanding fluorene-based conjugated molecules can be further optimized based on this universal building block.

Green-synthesized,low-cost tetracyanodiazafluorene(TCAF) as electron injection material for organic light-emitting diodes

Two electron-deficient azaacenes including di-and tetra-cyanodiazafluorene(DCAF and TCAF)with the advantages of deep lowest unoccupied molecular orbital(LUMO),green-synthesis,low-cost,simply purification method,excellent yields have been obtained,characterized and used as electron injection materials(EIMs)in three groups of electroluminescence devices.Device B with TCAF as EIM exhibited the best performance including turn-on voltage of 5.0 V,stronger maximum luminance intensity of 31,549 cd/m2,higher luminance efficiency of 62.34 cd/A and larger power efficiency of 21.74 lm/W which are 0.53,6.7,9.3 and 15.3 times than that of device A with DCAF as EIMs,respectively.The enhanced interfacial electron injection ability of TCAF than that of DCAF is supported by its better electron mobility in electron-only device,deeper LUMO(-4.52 eV),and stronger electronic affinity.Best external quantum efficiency of 16.56%was achieved with optimized thicknesses of TCAF as EIM and TPBi as electron transporting layer.As a new comer of acceptor family,TCAF would push forward organic electronics with more fascinating and significant applications.