Cosensitization process effect of D-A-π-A featured dyes on photovoltaic performances

Cosensitization based on two or multiple dyes as "dye cocktails" can hit the target on compensating and broadening light-harvesting region.Two indoline D-A-π-A motif sensitizers(WS-2 and WS-39) that possess similar light response area but distinctly reversed feature in photovoltaic performance are selected as the specific cosensitization couple. That is, WS-2 shows quite high photocurrent but low photovoltage, and WS-39 gives relatively low photocurrent but quite high photo voltage. Due to the obvious "barrel effect",both dyes show medium PCE around8.50%. In contrast with the previous cosensitization strategy mostly focused on the compensation of light response region, herein we perform different cosensitization sequence, for taking insight into the balance of photocurrent and photo voltage, and achieving the synergistic improvement in power conversion efficiency(PCE). Electronic impedance spectra(EIS) indicate that exploiting dye WS-39 with high V_(OC) value as the primary sensitizer can repress the charge recombination more effectively, resulting in superior V_(OC) rather than using dye WS-2 with high J_(SC)as the primary sensitizer. As a consequence, a high PCE value of 9.48% is obtained with the delicate cosensitization using WS-39 as primary dye and WS-2 as accessory dye, which is higher than the corresponding devices sensitized by each individual dye(around 8.48-8.67%). It provides an effective optimizing strategy of cosensitization how to combine the individual dye advantages for developing highly efficient solar cells.

Development of porphyrin-based fluorescent sensors and sensor arrays for saccharide recognition

Saccharide sensing is a very meaningful research topic as saccharides are involved in many biological activities.However,it is challenging to design molecular sensors for saccharides because this family of compounds is hydromimetic in aqueous solutions and shares a similar chemical structure.In this review,research progress in the development of porphyrin-based saccharide sensors is described with representative examples.We focus on using porphyrin as the signal reporter because porphyrins exhibit unique advantages in high chemical stability,long emission wavelength,and multiple structural modification strategies.Reported literature results have been classified into mainly two sections according to the general working principles of the porphyrin sensor molecules.In the first section,recognition unit,design strategy and sensing performance of traditional porphyrin-based selective saccharide sensors are discussed.While in the second section,development of porphyrin-based sensor arrays for pattern recognition of saccharides has been summarized.Looking through the design strategy and sensing performance of reported achievements,it is reasonable to anticipate a bright future for designing practical porphyrin-based saccharide sensors.

Enhancement strategies of targetability, response and photostability for in vivo bioimaging

Analyses of the physiology and pathology of active biochemical species in their native contexts are critical for early diagnosis and therapy. Optical imaging has emerged as one of the promising modalities for noninvasive and real-time visualization of important biomolecules or biological events, and it has witnessed major advances in the field of imaging in vitro and in vivo. In this review, we present a survey of common approaches and tactics for enhanced targetability, response rate, and photostability in bioimaging applications. Recently developed and representative examples are illustrated on the cellular and tissue levels.

Rational design of shortwave infrared(SWIR) fluorescence probe:Cooperation of ICT and ESIPT processes for sensing endogenous cysteine

Cysteine is well-known to be an important biothiol and related to many diseases. However, the in vivo detection of endogenous cysteine still suffers from lacking small-molecule fluorophores with both excitation and emission in the near-infrared(650-900 nm)/shortwave-infrared region. Herein, we report a molecular engineering strategy for shortwave infrared(SWIR, 900-1700 nm) sensing of cysteine, which integrated an excited-state intermolecular proton transfer(ESIPT) building block into the intramolecular charge transfer(ICT) scaffold. The obtained novel fluorophore SH-OH displays a maximum absorption at the NIR region, and emission at the SWIR region. We introduce the cysteine-recognition moiety to SH-OH structure, and demonstrate sensing of endogenous cysteine in living animals, using the SWIR emission as a reliable off-on fluorescence signal. This fluorophore design strategy of cooperation of ICT and ESIPT processes expands the in vivo sensing toolbox for accurate analysis in clinical applications.

Unsymmetrical donor—acceptor—donor—acceptor type indoline based organic semiconductors with benzothiadiazole cores for solution-processed bulk heterojunction solar cells

Bulk heterojunction(BHJ) solar cells based on small molecules have attracted potential attention due to their promise of conveniently defined structures, high absorption coefficients, solution process-ability and easy fabrication. Three D—A—D—A type organic semiconductors(WS-31,WS-32 and WS-52) are synthesized, based on the indoline donor and benzotriazole auxiliary acceptor core, along with either bare thiophene or rigid cyclopentadithiophene as π bridge, rhodanine or carbonocyanidate as end-group. Their HOMO orbitals are delocalized throughout the whole molecules. Whereas the LUMOs are mainly localized on the acceptor part of structure, which reach up to benzothiadiazole, but no distribution on indoline donor. The first excitations for WS-31 and WS-32 are mainly originated by electron transition from HOMO to LUMO level, while for WS-52, partly related to transition between HOMO and LUMO+1 level. The small organic molecules are applied as donor components in bulk heterojunction(BHJ) organic solar cells, using PC_(61)BM as acceptor material to check their photovoltaic performances. The BHJ solar cells based on blended layer of WS-31:PC_(61)BM and WS-32:PC_(61)BM processed with chloroform show overall photoelectric conversion efficiency(PCE) of 0.56% and 1.02%, respectively. WS-32 based BHJ solar cells show a higher current density originated by its relatively larger driving force of photo-induced carrier in photo-active layer to LUMO of PC_(61)BM.

An AIE-based enzyme-activatable fluorescence indicator for Western blot assay:Quantitative expression of proteins with reproducible stable signal and wide linear range

Western blot is a commonly used experimental method to analyze the protein expression.However,the most commonly used chromogenic indicator based on chemiluminescence is limited by narrow linear range and unstable quantitative reproducibility,whereas the recently developed fluorescent indicator suffers from poor detection limit.Herein,we report an enzyme-activatable fluorescence indicator to quantify proteins with reproducible stable signal and wide linear range,through introducing the hydrophilic alkaline phosphatase(ALP)-triggered phosphoric acid moiety into our established aggregation-induced emission(AIE)building block of quinoline-malononitrile(QM).In this strategy,the indicator DQM-ALP disperses well in both aqueous and lipid environments to exhibit initial“off”fluorescence,but when exposing to the ALP-coupled secondary antibody on the PVDF membrane,the specific enzymatic turnover would liberate hydrophobic AIE luminogen(AIEgen)QM-OH to emit strong luminescence,thereby achieving an ideal“off-on”state for sensitively imaging proteins with high signal-to-noise(S/N)ratio.Moreover,benefiting from the excellent signal stability of AIE fluorophore,DQM-ALP indicator exhibits superior quantitative analysis of protein expression with high reproducibility.Upon taking advantage of the AIEgens to reduce high concentration-induced luminance quenching,the linear quantification range is extremely expanded.In contrast with the traditional chemiluminescent indicator,the AIE-based enzymeactivatable indicator DQM-ALP not only greatly improves the signal stability for quantitative reproducibility,but also expands the linear quantification range,and further provides a practical alternative reagent for fluorescence Western blot assay.

Efficient p-i-n structured perovskite solar cells employing low-cost and highly reproducible oligomers as hole transporting materials

The development of p-i-n structured perovskite solar cells(PSCs) requires more extensive explorations on seeking efficient, low cost and stable hole transporting materials(HTMs). Small molecular HTMs are superior to polymeric ones in terms of synthetic reproducibility as well as purity. However, thin films composed of small molecules are usually labile during the solution-based perovskite deposition. Herein, we propose a molecular engineering strategy of incorporating oligothiophene as conjugation bridge to develop robust oligomer HTMs for p-i-n type PSCs. Upon increasing the oligothiophene chain length from α-bithiophene to α-quaterthiophene and α-hexathiophene, their HOMO energy levels remain unchanged, but their solubility in common organic solvents decreased remarkably, thus greatly enhancing their tolerance to the perovskite deposition. The rational design of oligothiophene chain length can effectively tune their optoelectronic properties as well as thin film stability under polar solvent soaking. The best performance is achieved by an α-quaterthiophene based HTM(QT), showing a high efficiency of 17.69% with fill factor of 0.81, which are comparable to those of a commercially available benchmark polymer HTM(poly[bis(4-phenyl)(2,4-dimethylphenyl) amine], PTAA) based devices fabricated under the same conditions. Our developed oligomer system not only provides the definite molecular structures like small molecule-type HTMs, but also exhibits the excellent filmforming like polymer-type HTMs, thus achieving the well-balanced parameters among solvent tolerance, thin film conductivity,and interfacial charge transfer efficiency, especially building up a platform to develop low cost and reproducible efficient HTMs in p-i-n structured perovskite solar cells.

A novel fluorescent probe for volatile amine vapor detection

In recent years,fluorescent probes have gained significant prominence in the field of substance analysis and detection[1–4].The development of high-performance volatile amine gas sensors is crucial for applications in food quality control,disease monitoring,and environmental protection[2].

A luminescence molecular switch via modulation of PET and ICT processes in DCM system

A novel versatile dicyanomethylene-4H-pyran(DCM) based derivative bearing ferrocenyl group(DCM-N-Fc) is designed as modulator to construct "off-on" logic operation. The optical properties of DCM-N-Fc are characterized by absorption and steady-state fluorescence technique, showing that the fluorescence from DCM chromophore via intramolecular charge transfer(ICT) is strongly quenched by photoinduced electron transfer(PET) process from ferrocene moiety. In contrast with the references(DCM-N and DCM-Fc), the fluorescence of DCM-N-Fc can be triggered by oxidizing ferrocenyl unit either chemically or electrochemically, exhibiting a characteristic emission modulation at around 610 nm with an electrofluorochromic behavior. Furthermore, the free energy and the fluorescence lifetime in the PET path verify the thermodynamic feasibility. Cyclic voltammetry, absorption spectroscopy, time-resolved fluorescence as well as DFT calculation have been used to elaborate the manipulation via both PET and ICT processes.

A new strategy enabling intramolecular motion to obtain advanced photothermal materials

Recently, considerable research interest has been focused on biomedical application of the photothermal materials, such as photoacoustic imaging (PAI) and photothermal therapy (PTT). PAI technique that roots in near-infrared (NIR) light excitation and ultrasonic detection has been extensively investigated in recent years since it surpasses the imaging depth limit of traditional optical imaging techniques, thereby providing deeper tissue penetration and higher spatial solution [1]. So far, several kinds of NIR-absorbing photothermal materials including gold nanorods/nanoshells, carbon nanotubes, 2D materials, semiconducting polymers and small-molecule organic dyes have been well studied for PAI and PTT.

Aggregation-induced emission: a coming-of-age ceremony at the age of eighteen

Aggregation-induced emission(AIE) has drawn great attention worldwide for its unique optical phenomenon and huge potential applications. Since coined by Ben Zhong Tang et al. in 2001, AIE has been deeply investigated and widely utilized in many important areas, such as organic light-emitting diode(OLED), sensor, and bio-imaging. Herein, we highlight some important progress of AIE in these eighteen years, including the exploration of internal mechanism and potential applications. Furthermore,some other interestingly emissive behaviors, originating but distinguishing from the AIE concept, are presented. It is anticipated an overall understanding about AIE could be easily caught from this short review for scientists, no matter whether they are involved in this exciting and rising research area or not.

A novel colorimetric and ratiometric NIR fluorescent sensor for glutathione based on dicyanomethylene-4H-pyran in living cells

Glutathione(GSH)plays a critical role in maintaining oxidation-reduction homeostasis in biological systems.Considering the detection of GSH by fluorescence sensors is limited by either the short wavelength emission or the poor photostability,a highly stable colorimetric and ratiometric NIR fluorescent sensor(DCM-S)for GSH detection has been constructed on the basis of dicyanomethylene-4H-pyran(DCM)chromophore.The specific disulfide bond is incorporated via a carbamate linker as the GSH responsive group,which simultaneously blue-shifts and quenches the fluorescence.Upon addition of GSH,DCM-S exhibits outstanding colorimetric(from yellow to red)and ratiometric fluorescent response with the 6-fold enhancement of NIR fluorescence at 665 nm in quantum yield.More importantly,the GSH-treated DCM-S(DCM-NH_2 actually)possesses 20-fold longer fluorescence half-life period as well as much better photostability than the FDA-approved ICG.Finally,the ratiometric detection of GSH is also successfully operated in the living cell imaging,exhibiting NIR fluorescence and large Stokes shift(215 nm)with nearly no background fluorescence interference.As a consequence,DCM-S can be utilized as colorimetric and ratiometric NIR fluorescent sensor for GSH,with a great potential in the development of GSH-induced drug delivery system.

Reversible light-driven magnetic switching of salen cobalt complex

Spin-crossover(SCO)metal complexes are expected to be widely used in data storage materials,display devices and sensors.Although a lot of spin-crossover photoswitches have been developed,the reversible photomodulation cases that work at room temperature are limited.Herein,a novel cobalt complex o-1-Co(II)wherein the salen unit bridges with bis-diarylethene has been designed as switch to construct"off-on"logic operation at room temperature.The complex o-1-Co(II)displays an abrupt,reversible and hysteretic spin crossover(T1/2↓=166 K,T1/2↑=177 K,andΔT1/2=11 K)between the high-spin(HS)and low-spin(LS)states.Meanwhile,photocyclization of o-1-Co(II)with UV light produces a photoresponsive closed form c-1-Co(II),which always stays at low-spin without SCO at all.Moreover,the magnetic switching of the complex can also be achieved with redox reactions between Co(II)and Co(III).

Amazing long-lived lifetime

Bulk thanks to their characteristics of being environmentally benign,easily fabricated and relatively stable,dyesensitized solar cells(DSSCs)have attracted attention over decades as a potential alternative to solar energy conversion[1].However,as L.M.Peter pointed out in 2011,'although much more is now known about the physical and chemical processes taking place during operation of the DSSCs,the exponential increase in research effort during this period has not been matched by large increases in efficiency'[2].To date,

Type I photosensitizer based on AIE chromophore tricyano-methylene-pyridine for photodynamic therapy

Image guided photodynamic therapy(PDT)combines fluorescence tracing and phototherapy,which can achieve a more accurate and effective treatment effect.However,traditional photosensitizers are limited by the aggregation-caused fluorescence quenching(ACQ)effect and low reactive oxygen species(ROS)generation in a hypoxic environment,resulting in poor imaging and treatment effect.Herein,we report a tricyano-methylene-pyridine(TCM)-based Type I aggregation-induced emission(AIE)photosensitizer(TCM-MBP),the strong elec-tron acceptance(D-A)effect extends the wavelength to near-infrared(NIR)region to reduce the autofluorescence interference,and oxygen atoms provide lone pair electrons to enhance the inter system crossing(ISC)rate,thereby promoting the generation of more triplet states to produce ROS.The AIE photosensitizer TCM-MBP exhibited low oxygen dependence,NIR emission,and higher ROS production compared to commercially avail-able Ce_(6) and RB.After encapsulation with DSPE-PEG 2000,TCM-MBP nanoparticles(TCM-MBP NPs)could penetrate to visualize cells and efficiently kill cancer cells upon light irradiation.This study provides an oxygen-independent AIE photosensitizer,which has great potential to replace the commercial ACQ photosensitizers.

Organic sensitizers with different thiophene units as conjugated bridges:molecular engineering and photovoltaics

Three structural modifications with incorporation of alkyl,alkoxy and vinyl bond into the skeleton of thiophene bridge in D-π-A featured organic sensitizers are specifically developed for insight into their influences on photophysical,electrochemical as well as photovoltaic properties in nanocrystalline TiO_2-based dye sensitized solar cells(DSSCs).The insertion of vinyl bond into the conjugation bridge leads to the molecular planar configuration,and the conjugation bridge of 3,4-ethylenedioxythiophene(EDOT)is prone to positively shift its highest occupied molecular orbital(HOMO).The electrochemical impedance spectroscopy(EIS)results indicate that the grafted long alkyl chain onto thiophene is favorable to suppress dye aggregation when adsorbed onto TiO_2film and modification on interface of TiO_2/dye/electrolyte,resulting in a relatively high open-circuit voltage(V_(oc)).Under optimized conditions,dye LS-4 bearing hexylthiophene as the conjugation bridge shows a relatively high overall conversion efficiency of5.45%,with a photocurrent of 11.61 mA cm^(-2),V_(oc)of 744 mV.

Photoresponsive aggregation-induced emission polymer film for anti-counterfeiting

The development of solid-state smart materials, in particular those showing photoresponsive luminescence, is highly desirable for their cutting edge applications in displays, sensors, data-storage, and anticounterfeiting. However, to achieve both excellent photoresponsive performance and bright luminescence in solid state remains challenge. Herein, we integrate a novel photochromic fluorophore YL into flexible polymer chains, thereby enabling the resultant polymer PYL with reversible photoisomerization upon aggregation. Remarkably, the polymer PYL possesses excellent photochromic properties and aggregationinduced emission(AIE) activity, which can be attributed to the photoactive YL moiety. Upon light exposure, its film exhibits reversibly off-to-on fluorescent modulation with quick response, high emission efficiency and signal contrast, sharply different from the weak emission in solution. The novel photoresponsive AIE polymer with invisible/visible color and fluorescence transformation allows for advanced anti-counterfeiting applications. This work provides an efficient platform for constructing solid-state photocontrollable luminescent materials.

Controllable Fragrance Release Mediated by Spontaneous Hydrogen Bonding with POSS–Thiourea Derivatives

The purpose of achieving the long-lasting fragrance perception leads to nanocarrier-based profragrances in perfume applications.Herein,we report a family of novel profragrance systems based on polyhedral oligomeric silsesquioxane(POSS)derivatized thioureas(POSS thioureas)that enable linkage of volatile carbonyl fragrances with the spontaneous formation of fragile hydrogen bonds.This profragrance platform addresses the dilemma of the volatile nature of aroma-materials on the one hand,and the desired long-lasting effects on the other.Their releasing performance as profragrances is investigated by headspace solid-phase microextraction(SPME)in combination with gas chromatography(GC)analysis under water as the external humidity stimulus,indicating that the fragrance concentration released from the POSS–thiourea-based profragrance is up to four times higher than the neat reference of the corresponding perfume aldehydes.Furthermore,deposition of the novel profragrance system onto wallpaper results in excellent retentive capacity for volatile aldehydes.Given the low essential toxicity,the POSS–thiourea system has been demonstrated as a suitable profragrance for practical application to perfume delivery.

Engineering photo-controllable fragrance release with flash nanoprecipitation

Controllable profragrance nanoparticles are in great demand for long-lasting scent in flavor and fragrance industries.However,the practical applications of controllable fragrance release are limited by the non-tunable size,structural heterogeneity and poor reproducibility.Herein,a coumarin-derived phototrigger(CM-OH)is covalently conjugated with alcohol fragrances to obtain the corresponding profragrances(CM-R)which enable to release fragrances under the light controlling conditions.Furthermore,we introduce a new engineering strategy to construct fine tunable and highly uniform profragrance nanoparticles with flash nanoprecipitation(FNP)technology,which features commercial available amphiphilic pluronic F127 polymers by encapsulation of photoactivatable profragrances CM-R in hydrophobic cores to enhance the long-lasting photo-controllable fragrance release.With the assistance of FNP technology,amphiphilic pluronic polymer and profragrances CM-R in organic solution are instantaneously mixed and subsequently precipitated in the multi-inlet vortex mixer(MIVM),thus obtaining the pluronic F127-encapsulated profragrance nanoparticles with good homogeneity.Compared to the traditional thermodynamic encapsulation method,the novel kinetic FNP technology can not only tune the size of profragrance nanoparticles with narrow distribution,but also distinctly improve the batch-to-batch reproducibility,which affords an alternative method for scale-up preparation of amphiphilic profragrance nanoparticles in precisely controllable fragrance delivery system.