Effects of nonaromatic through-bond conjugation and through-space conjugation on the photoluminescence of nontraditional luminogens

Photoluminescence(PL)mechanisms of nontraditional luminogens(NTLs)have attracted great interest,and they are generally explained with intra/intermolecular through-space conjugation(TSC)of nonconventional chromophores.Here a new concept of nonaromatic through-bond conjugation(TBC)is proposed and it is proved that it plays an important role in the PL of NTLs.The PL behaviors of the three respective isomers of cyclohexanedione and gemdimethyl-1,3-cyclohexanedione were studied and correlated with their chemical and aggregate structures.These compounds show differentfluorescence emissions as well as dif-ferent concentration,excitation and solvent-dependent emissions.The compounds which undergo keto-enol tautomerism and hence with a conjugated ketone-enol structure(i.e.,nonaromatic TBC)show more red-shifted emissions.TBC effect reduces the energy gaps and facilitates the formation of stronger TSC in the aggre-gate state.The compounds in the ketone-enol form are also prone to occur excited state intra/intermolecular proton transfer(ESIPT).The cooperative effect of nonaro-matic TBC and TSC determines the PL behaviors of NTLs.This work provides a novel understanding of the PL mechanisms of NTLs and is of great importance for directing the design and synthesis of novel NTLs.

Highly Emissive Luminogens in Both Solution and Aggregate States

Organic light-emitting materials have attracted considerable attention because of their promising applications in diverse areas.Most fluorophores emit brightly in either dilute solutions or aggregate states;the former generally suffer from aggregation-caused quenching problem,and the latter encounter intensity loss at low concentrations.Herein,we propose a new strategy to overcome these dilemmas by balancing the planar and distorted structures of terphenyl-based luminogens and obtain three luminogens,2PB-AC,2Me2PB-AC,and 2T2PB-AC,with bright emission in both solution and aggregate states.Among them,2PB-AC shows absolute photoluminescence quantum yields(ФPL)higher than 90%in both tetrahydrofuran solution(90.2%)and aggregate states(92.7%for powder and 95.3%for crystal).Thus,2PB-AC could be an efficient probe to realize dual-channel explosive detection in both solution and aggregate states.Moreover,it could be used to image live-cell lipid droplets at a wide range of concentrations.In addition,benefiting from its thermodynamically favorable intersystem crossing process,2Me2PB-AC could be doped in polymethyl methacrylate matrix to provide efficient room-temperature phosphorescence.Thus,this work provides a feasible strategy for the design of luminogens with highly efficient emission in both solution and aggregate states,greatly facilitating and broadening their practical applications.

Crystallization-induced phosphorescence of pure organic luminogens

This review summarizes the recent progress of efficient room temperature phosphorescence（RTP） from pure organic luminogens achieved by crystallization-induced phosphorescence（CIP）,with focus on the advances in our group.Besides homocrystals,mixed crystals and cocrystals are also discussed.Meanwhile,intriguing RTP emission from the luminogens without conventional chromophores is demonstrated.

Stimulus-responsive room temperature phosphorescence in purely organic luminogens

Luminogens that exhibit stimulus-responsive room temperature phosphorescence(RTP)have attracted significant attention for their applications in a wide range of fields such as data storage,sensors,and bio-imaging.However,very few such materials are known,partly because of the unclear internal mechanism.In this review,we summarize recent advances in the field of stimulusresponsive RTP in purely organic luminogens,focusing on their unique emission behaviors and internal mechanisms governing the phenomena.We also attempt to identify the relationship between the mechanism,luminogens,and possible applications.

A gelable pure organic luminogen with fluorescence-phosphorescence dual emission

Pure organic luminogens with room temperature phosphorescence(RTP) have drawn much attention due to their fundamental importance and promising applications in optoelectronic devices, bioimaging, sensing, etc. Fluorescence-phosphorescence dual emission at room temperature, however, is rarely observed in pure organic materials. Herein, we reported a metal-and heavy-atom free pure organic luminogen with tert-butyl groups, DtBuCZBP, which is ready to form organogels in dimethylsulfoxide(DMSO).It emits prompt and delayed fluorescence, as well as RTP, namely dual emission in as-prepared solid, gels and polymeric films.To the best of our knowledge, it is the first example of metal-and heavy-atom free pure organic gelator with RTP emission. Such unique RTP and moreover dual emission properties in different states make DtBuCZBP a potential material for diverse applications.

Exceptionally efficient deep blue anthracene-based luminogens:design,synthesis,photophysical,and electroluminescent mechanisms

Achieving high-efficiency deep blue emitter with CIE_(y)<0.06(CIE,Commission Internationale de L’Eclairage)and external quantum efficiency(EQE)>10%has been a long-standing challenge for traditional fluorescent materials in organic light-emitting diodes(OLEDs).Here,we report the rational design and synthesis of two new deep blue luminogens:4-(10-(4’-(9 H-carbazol-9-yl)-2,5-dimethyl-[1,1’-biphe nyl]-4-yl)anthracen-9-yl)benzonitrile(2 M-ph-pCzAnBzt)and 4-(10-(4-(9 H-carbazol-9-yl)-2,5-dimethyl phenyl)anthracen-9-yl)benzonitrile(2 M-pCzAnBzt).In particular,2 M-ph-pCzAnBzt produces saturated deep blue emissions in a non-doped electroluminescent device with an exceptionally high EQE of 10.44% and CIE_(x,y)(0.151,0.057).The unprecedented electroluminescent efficiency is attributed to the combined effects of higher-order reversed intersystem crossing and triplet-triplet up-conversion,which are supported by analysis of theoretical calculation,triplet sensitization experiments,as well as nanosecond transient absorption spectroscopy.This research offers a new approach to resolve the shortage of high efficiency deep blue fluorescent emitters.

Molecular uniting set identified characteristic(MUSIC): a promising strategy for purely organic RTP luminogens

The room temperature phosphorescences（RTP）are of growing interest owing to their promising applications in material science and bioimaging.To date,the lumiogens showing persistent RTP effect mainly contain the noble metals which have the shortcomings such as high cost,potential toxicity.The exploration of metal free luminogens,i.e.,purely organic RTP luminogens,is thus of great importance for the community.

Polymorphism dependent triplet-involved emissions of a pure organic luminogen

Polymorphism has been frequently used in tuning the singlet emissions of pure organic dyes. The modulation of triplet-involved emissions, particularly room temperature phosphorescence(RTP),however, is scarcely reported. Herein, polymorphism is reported to tune the triplet-involved emissions of 2 CZBZL, a newly designed pure organic luminogen consisting of twisted benzil and two planar carbazole moieties. Other than the conventional modulation through changing molecular conformation and packing, vibration can also finely tune the triplet-involved emissions. Besides prompt fluorescence(PF),polymorph B with relatively extended conformation emits thermally activated delayed fluorescence(TADF), whereas the others(A, C–E) with similarly more twisted conformations generate predominant RTP or simultaneous DF and RTP. These results demonstrate the fascinating chance to regulate the tripletinvolved emissions through controlling conformation and vibration.

D-A structured high efficiency solid luminogens with tunable emissions： Molecular design and photophysical properties

Fabrication of efficient solid luminogens with tunable emission is both fundamentally significant and technically important. Herein, based on our previous strategy for the construction of efficient and multifunctional solid luminogens through the combination of diverse aggregation-induced emission （ALE） units with other functional moieties, a group of luminophores with electron donor-acceptor （D-A） structure and typical intramolecular charge transfer （ICT） characteristics, namely CZ-DCDPP, DPA-DCDPP and DBPA-DCDPP were synthesized and investigated. The presence of twisting and AlE-active 2,3- dicyano-S,6-diphenylpyrazine （DCDPP） moiety endows them highly emissive in the solid states, whereas the introduction of arylamines with varied electron-donating capacity and different conjugation render them with tunable solid emissions from green to red. While CZ-DCDPP and DPA-DCDPP solids exhibit distinct mechanochromism, both DPA-DCDPP and DBPA-DCDPP solids can generate efficient red emission. Owing to their high efficiency, remarkable thermal and morphological stabilities and moreover red emission, they are promising for diverse optoelectronic and biological applications.

基于蒽醌的红色延迟荧光材料的设计合成及光电性质

由于受到能隙定律的严重约束,激发态的有机红光材料的非辐射衰减较大,从而导致其荧光量子产率普遍较低。该文利用电子给/受体(donor-acceptor,D-A)之间不同的连接方式,在有无苯环作为π桥的情况下合成了AQ-2DPAC和AQ-2PDPAC两种红光蒽醌材料。并系统地研究了上述两种材料的电子结构、热性能、光物理性能和电致发光性能,以评估苯环作为π桥对材料发光性能的影响。两种蒽醌材料采取高度扭曲构造,均具有优良的聚集诱导发光和延迟荧光特性。该研究表明,就两种电荷转移发光材料而言,苯环作为π桥的引入使D-A得到了更有效的分离,并减小了最低单重态和三重态激发态之间的能级差,提高了辐射复合速率,从而提高荧光量子产率。因此,荧光量子产率从D-A型分子AQ-2DPAC的19%显著提升至D-π-A型分子AQ-2PDPAC的52%。采用AQ-2PDPAC发光材料的有机发光二极管器件性能更为优异,最大外量子效率为13.7%,最大亮度为12260 cd·m^(-2)。

Machine learning-based real-time visible fatigue crack growth detection

Many large-scale and complex structural components are applied in the aeronautics and automobile industries.However,the repeated alternating or cyclic loads in service tend to cause unexpected fatigue fractures.Therefore,developing real-time and visible monitoring methods for fatigue crack initiation and propagation is critically important for structural safety.This paper proposes a machine learning-based fatigue crack growth detection method that combines computer vision and machine learning.In our model,computer vision is used for data creation,and the machine learning model is used for crack detection.Then computer vision is used for marking and analyzing the crack growth path and length.We apply seven models for the crack classification and find that the decision tree is the best model in this research.The experimental results prove the effectiveness of our method,and the crack length measurement accuracy achieved is 0.6 mm.Furthermore,the slight machine learning models help us realize real-time and visible fatigue crack detection.

D-π-A-π-D型小分子红光材料的制备及其性能

开发新型有机红光材料对于制备高性能红光有机电致发光器件具有重要的研究意义。本文采用SUZUKI偶联反应,以芴酮为受体(A)、3,4,5-三甲氧基苯为给体(D)合成了新型D-π-A-π-D结构的有机红光材料(3MeFO)。通过1H NMR谱、13 C NMR谱和X单晶衍射确认了分子结构,该化合物展示了较强的电荷转移作用和良好的共轭结构,其晶体的发射峰达到620 nm。从单晶结构中看出甲氧基的引入有利于在分子间形成大量的氢键,有效地增强了分子间的相互作用。同时,该材料表现出良好的热稳定性能和电化学性能,使得其在OLED中展示了良好的电致发光性能。

基于近红外聚集诱导发光分子的磁性纳米材料用于光增强杀菌

近红外光敏剂由于荧光成像具有光损伤小、穿透力强和空间分辨率高等优点,能显著提高光动力治疗效果。我们合成了近红外聚集诱导探针5,6-2(4′-(二苯氨酚)-[1,1′-联苯]-4-yl)吡嗪-2,3-二甲腈(DCDPP-2TPA)用于光增强杀菌。利用聚集态/固态下荧光增强的优势,DCDPP-2TPA与磁性Fe_(3)O_(4)纳米材料复合,产生更高活性氧(ROS)用于杀菌。利用SEM、TEM、XRD和荧光光谱研究了该复合材料的结构和性质,并用于大肠杆菌和金黄色葡萄球菌杀菌实验。结果表明,在光照下两种细菌的存活率为7.5%与9.0%,优于DCDPP-2TPA(10%与14%)。同时该复合材料可以方便地实现磁性分离,在光照下产生ROS后循环杀菌。

Emission or scattering?Discriminating the origin of responsiveness in AIEgen-doped smart polymers using the TPE dye

Aggregation-induced emission(AIE)luminogens are attractive dyes to probe poly-mer properties that depend on changes in chain mobility and free volume.When embedded in polymers the restriction of intramolecular motion(RIM)can lead to their photoluminescence quantum yield(PLQY)strong enhancement if local microviscosity increases(lowering of chain mobility and free volume).Nonethe-less,measuring PLQY during stimuli,i.e.heat or mechanical stress,is technically challenging;thus,emission intensity is commonly used instead,assuming its direct correlation with the PLQY.Here,by usingfluorescence lifetime as an absolutefluorescence parameter,it is demonstrated that this assumption can be invalid in many commonly encountered conditions.To this aim,different poly-mers are loaded with tetraphenylenethylene(TPE)and characterized during the application of thermal and mechanical stress and physical aging.Under these con-ditions,polymer matrix transparency variation is observed,possibly due to local changes in refractive index and to the formation of microfractures.By combin-ing different characterization techniques,it is proved that scattering can affect the apparent emission intensity,while lifetime measurements can be used to ascertain whether the observed phenomenon is due to modifications of the photophysi-cal properties of AIE dyes(RIM effect)or to alterations in the matrix optical properties.

An overview on AIEgen-decorated porphyrins:Current status and applications

One of the major obstacles of porphyrins is the aggregation-caused quenching(ACQ)of photoluminescence due to the strong intermolecularπ–πinteraction of the planar porphyrin core in the solid state.However,ACQ leads to the nonradiative deactivation of the photoexcited states which results in short-lived charge-separated states and thus low photoluminescence and singlet quantum yields.This phenomenon would limit the utilization of porphyrins in near-infrared fluorescent bioimaging,photodynamic therapy,photocatalytic hydrogen evolution,electrochemiluminescence,and chiroptical applications.Hence,to address the ACQ property of porphyrins and enhance the performance of the above applications,a limited number of AIEgen-decorated porphyrins have been designed,synthesized,and tested for their applications.It has been found that the introduction of AIEgens,such as tetraphenylethylene,diphenylacrylonitrile,(3,6-bis-(1-methyl-4-vinylpyridinium)-carbazole diiodide,and iridium motif into the porphyrin core,transformed the porphyrins from ACQ to aggregation-induced emission(AIE)in their solid state due to the reduced strong intermolecularπ–πstacking of porphyrins.Consequently,such porphyrins containing AIE features are employed as potential candidates in the above-mentioned applications.In this review,we summarize the AIEgen-decorated porphyrins which have been published to date,and also discuss the benefits of converting porphyrins from ACQ to AIE for enhanced performance within each application.As far as we know,there is no review that summarizes the structures and applications of AIEgen-decorated porphyrins to date.Therefore,we presume that this review would be helpful to design more efficient AIEgen-decorated porphyrins for a wide range of applications in the future.

An AIEgen/graphene oxide nanocomposite(AIEgen@GO)-based two-stage“turn-on”nucleic acid biosensor for rapid detection of SARS-CoV-2 viral sequence

The ongoing outbreak of Severe Acute Respiratory Syndrome Coronavirus 2(SARS-CoV-2)pandemic has posed significant challenges in early viral diagnosis.Hence,it is urgently desirable to develop a rapid,inexpensive,and sensitive method to aid point-of-care SARS-CoV-2 detection.In this work,we report a highly sequence-specific biosensor based on nanocomposites with aggregationinduced emission luminogens(AIEgen)-labeled oligonucleotide probes on graphene oxide nanosheets(AIEgen@GO)for one step-detection of SARS-CoV-2-specific nucleic acid sequences(Orf1ab or N genes).A dual“turn-on”mechanism based on AIEgen@GO was established for viral nucleic acids detection.Here,the first-stage fluorescence recovery was due to dissociation of the AIEgen from GO surface in the presence of target viral nucleic acid,and the second-stage enhancement of AIEbased fluorescent signal was due to the formation of a nucleic acid duplex to restrict the intramolecular rotation of the AIEgen.Furthermore,the feasibility of our platform for diagnostic application was demonstrated by detecting SARS-CoV-2 virus plasmids containing both Orf1ab and N genes with rapid detection around 1 h and good sensitivity at pM level without amplification.Our platform shows great promise in assisting the initial rapid detection of the SARS-CoV-2 nucleic acid sequence before utilizing quantitative reverse transcription-polymerase chain reaction for second confirmation.

Clustering-triggered Emission of Cellulose and Its Derivatives

In recent years, nonconventional luminogens free of aromatic groups have attracted extensive attention due to their academic importance and promising wide applications. Whilst previous studies generally focused on fluorescence from aliphatic amine or carbonylcontaining systems, less attention has been paid to room temperature phosphorescence(RTP) and the systems with predominant oxygen functionalities. In this work, photophysical properties of the polyhydroxy polymers, including microcrystalline cellulose(MCC), 2-hydroxyethyl cellulose(HEC), hydroxypropyl cellulose(HPC), and cellulose acetate(CA), were studied and compared. While MCC,HEC, and HPC solids showed bright emission alongside distinct RTP, CA demonstrated relatively low intensity of solid emission without noticeable RTP. Their emissions were explained in terms of the clustering-triggered emission(CTE) mechanism and conformation rigidification. Additionally, on account of its intrinsic emission, concentrated HEC aqueous solution could be used as the probe for the detection of 2,4,6-trinitrophenol(TNP).

Organic luminescent materials:The concentration on aggregates from aggregation-induced emission

The research of organic luminescent materials in aggregate has drawn more and more attention for their wide applications.To adjust the luminescent properties for aggregates,a deep understanding of the corresponding internal mechanism is needed.In this short review,a brief introduction of aggregation-induced emission(AIE)and some other solid state luminescence behaviors derived from or parallel to AIE is presented.Particularly,the relationship between emission property and intermolecular/intramolecular interactions is summarized,with the aim to guide the further development of organic optoelectronic materials in aggregate.

Organic molecular aggregates:From aggregation structure to emission property

Organic molecular aggregates have attracted widespread attention over the past decade owing to their unique optoelectronic properties in the aggregate state,which mainly involves the effects of aggregation structure as well as molecular packing mode.Although many examples of H-and J-aggregates defined by molecular exciton model have been found,there are also other types of unconventional aggregates,especially for aggregation-induced emission(AIE)system.In this review,the recent progress of some examples of basic and novel aggregate forms,as well as coassembled forms,presenting distinctive optical features,such as optical waveguide and polarization emission,polymorph-dependent emission and stimuli-responsive luminescence are presented.The systematic insight into the relationship between the aggregation structure and emission property is discussed.Guidelines are therefore anticipated and will direct the future preprogramming molecular design so as to fine-tune the emission feature through a specific aggregation model for developing organic molecular aggregates with desirable optoelectronic properties.

Synthesis,optical properties and self-organization of blue-emitting butterfly-shaped dithienobenzosiloles

Ten novel butterfly-shaped dithienobenzosilole-based luminogens,which are peripherally installed with a variety of substituents including hydrogen,phenyl and substituted phenyl groups,have been readily prepared via an iodine-induced intramolecular electrophilic double-cyclisation reaction and subsequent deiodination or coupling reactions.The optical and electrochemical properties of these compounds were systematically investigated to clarify the relationships between their structures and properties,supported by theoretical calculations.These compounds exhibit deep-blue to sky-blue emissions and high photoluminescence quantum yields up to 0.84 in solution and solid states which are regulated by the functional blades and their steric hindrance on theα–andβ–positions of thiophene rings.Their high thermal-and photo-stabilities have been revealed and mainly attributed to the dithienobenzosilole core.