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Broad applications of electropolymerized conducting polymers (CPs) often prefer thinner soft electrodes to comply with downscaling of the fabrication resolution. However, high conductivity of existing CP films vanishes as thickness decreases to the nanoscale (i.e., below 100 nm), with an unclear mechanism so far. In this study, with an unprecedented family of polypyrrole (PPy) nanofilms that can be easily transferred in a fast and contamination-free manner, we are able to trace the initial development of electrical conductance along with chains' arrangement starting from the very early electrochemical deposition. Our results evidence that the classical nodular polymeric aggregation fundamentally accounts for the persistent losses of interchain connectivity and macroscopic conductivity at a limited thickness. Surprisingly, this seemingly disadvantageous structure can be altered into a large conjugated network to robustly restore the conductivity back to over 80 S cm-1 even below 100 nm, while the controllable formation, growth, and collapse of such networks radically vary the conductivity over a range of 3 orders of magnitude (0.8-129 S cm-1). These observations depict the first physical picture detailing how the long-range conductivity builds up in a growing conjugated network, which opens a route to fast synthesis and diverse applications of such highly conductive CP nanofilms.

A water-soluble phosphorescent bioprobe was successfully developed by introducing an iridium(III) complex as a phosphorescent signaling unit with poly(N-isopropylacrylamide) (PNIPAM) as the stimuli-responsive backbone. The probe was used for the effective detection of cysteine (Cys)/homocysteine (Hcy) and temperature based on changes in the phosphorescence signal. The design principle was based on the fact that the aldehyde groups in the cyclometalated ligands of the iridium(III) complex moiety can react with the β- or γ-aminothiol group to form thiazolidine or thiazinane, respectively, resulting in a phosphorescence change in the iridium(III) complex, thereby facilitating the detection of Cys and Hcy. Moreover, a phosphorescent hydrogel based on this probe was formed upon cross-linking and was then used as a quasi-solid sensing system for detecting Cys and Hcy. Furthermore, by using a time-resolved photoluminescence technique, the probe can detect Hcy in the presence of intense background fluorescence. In addition, phase changes in temperature-responsive PNIPAM can result in a switch of microenvironment between hydrophilicity and hydrophobicity, to which the phosphorescent emission of the iridium(III) complex is very sensitive. This bioprobe integrates water solubility, biocompatibility, and sensing capability into one system, which is advantageous for biological applications. Further investigation of the application of the bioprobe for living-cell imaging confirmed that the probe is membrane permeable and is capable of detecting Cys in living cells with notable phosphorescence enhancement. Fluorescence lifetime imaging microscopy is successfully applied for sensing and bioimaging of intracellular Cys in the presence of short-lived background fluorescence.

We design an organic photosensitizer with a donor-π-acceptor configuration. The photosensitizer exhibits aggregation-induced emission characteristics and efficient singlet oxygen production in the aggregated state. It is then enveloped into the water-soluble micelle to afford a nanoprobe. The water-soluble nanoprobe keeps the photosensitizer in the aggregation state and is used for imaging-guided photodynamic ablation of cancer cells.

Photothermal therapy (PTT) as a kind of noninvasive tumor treatment has attracted increasing research interest. However, the efficiency of existing PTT agents in the near-infrared (NIR) region is the major problem that has hindered further development of PTT. Herein, we present an effective strategy to construct the efficient photothermal agent by utilizing an intramolecular photoinduced electron transfer (PeT) mechanism, which is able to dramatically improve photothermal conversion efficiency in the NIR region. Specifically, an NIR dye (A1) constructed with dimethylamine moiety as the electron donor and the aza-BODIPY core as the electron acceptor is designed and synthesized, which can be used as a class of imaging-guided PTT agents via intramolecular PeT. After encapsulation with biodegradable polymer DSPE-mPEG5000, nanophotothermal agents with a small size exhibit excellent water solubility, photostability, and long-time retention in tumor. Importantly, such nanoparticles exhibit excellent photothermal conversion efficiency of ∼35.0%, and the PTT effect in vivo still remains very well even with a low dosage of 0.05 mg kg-1 upon 808 nm NIR laser irradiation (0.5 W cm-2). Therefore, this reasonable design via intramolecular PeT offers guidance to construct excellent photothermal agents and subsequently may provide a novel opportunity for future clinical cancer treatment.

Organelle-targeted photosensitizers have been reported to be effective photodynamic therapy (PDT) agents. In this work, we designed and synthesized two iridium(III) complexes that specifically stain the mitochondria and lysosomes of living cells, respectively. Both complexes exhibited long-lived phosphorescence, which is sensitive to oxygen quenching. The photocytotoxicity of the complexes was evaluated under normoxic and hypoxic conditions. The results showed that HeLa cells treated with the mitochondria-targeted complex maintained a slower respiration rate, leading to a higher intracellular oxygen level under hypoxia. As a result, this complex exhibited an improved PDT effect compared to the lysosome-targeted complex, especially under hypoxia conditions, suggestive of a higher practicable potential of mitochondria-targeted PDT agents in cancer therapy.

Mercury is one of the most hazardous and ubiquitous heavy metals, which may accumulate in human body through the food chain. [ 1 ] It shows high permeability into skin, respiratory and gastrointestinal systems of the human body, and can cause serious damage to the central nervous system. [ 2 ] Therefore, it is very important to develop various methods to effi ciently detect mercury in vitro and in vivo. Luminescence bioimaging provides an important means of visualizing morphological details of tissues with subcellular resolution and has become a powerful tool for manipulation in the biological analysis and medical diagnosis and treatment. [ 3 ]

Delayed fluorescence (DF) materials have shown great potential in time‐resolved luminescence imaging (TRLI), due to the relatively elongated emission lifetimes. However, the sensitivity of DF to environmental quenching leads to a challenge to realize TRLI directly using pure thermally‐activated DF (TADF) molecules. Herein, two TADF molecules, namely CzPOTCF and tBCzPOTCF, are designed and synthesized, featuring a diphenylphosphine oxide (DPPO) group substituted at the ortho‐position of the carbazole group. Compared with DPPO‐free CzTCF, the steric hindrance of DPPO groups enlarges dihedral angles between TCF and the carbazole groups in CzPOTCF and tBCzPOTCF; meanwhile, PO provides other channels for forming intermolecular hydrogen bonds. The optimized intermolecular interactions facilitate the dimer formation of CzPOTCF and tBCzPOTCF, which simultaneously enhance aggregation‐induced DF and mitigate disordered packing‐induced quenching. As a consequence, CzPOTCF and tBCzPOTCF show the enhanced aggregation‐induced DF with largely increased lifetimes. Without any additional assistance, the long‐lived fluorescence of CzPOTCF and tBCzPOTCF is successfully observed for cell TRLI, with 1–1.7 μs elongated average lifetimes of 6.69 and 7.41 μs, respectively.

A phenazine derivative with a succinimide endcap (PHS) was designed and synthesized for cysteine (Cys) with near-infrared (NIR) emission. Upon the addition of Cys, the color of the solution changed clearly from greenish black to orange, which was attributed to the disappeared absorbance at 616 nm. An enhanced NIR emission band at 670 nm was found in the fluorescence spectra and a corresponding excitation peak at 466 nm arose in the excitation spectra. Verified by the dynamic reaction, the cyanoacetic acid moiety should be susceptible to be attacked by the –SH group in a fast rate through Michael addition reaction. Being highly reactive to the amino group (–NH2), the NHS-active carbonyl site could target the amino acid and accelerate the process of nucleophilic attack from the –SH group. This cycloaddition mechanism of the α,β-unsaturated carbonyl NHS-ester was proved by 1H NMR titration. In addition to its good biocompatibility, PHS was successfully applied to the detection of Cys in Hela cell lines with NIR fluorescence signals.

Cysteine (Cys) plays crucial roles in biological systems and in mitochondrial processes. Highly selective probes for specific detection of mitochondrial Cys over other biological thiols are rare. Herein, we designed and synthesized a mitochondria-targetable near-infrared (NIR) fluorescent off-on probe, NFL1, based on a fluorescein derivative for Cys detection. Probe NFL1 has a lipophilic cation unit as the mitochondria biomarker and an acrylate group as the Cys-recognition unit as well as a fluorescence quencher. The probe itself is nonfluorescent due to the photoinduced electron transfer process. Upon addition of Cys, marked enhancement in the NIR emission (735 nm) can be monitored due to cleavage of the acrylate moiety. This probe had great sensitivity and selectivity for the rapid detection of Cys over homocysteine (Hcy) and glutathione (GSH) with an ultralow detection limit of 14.5 nM. More importantly, the probe successfully targeted mitochondria, detected endogenous Cys, and assessed mitochondrial oxidative stress in living cells. Probe NFL1 was also capable of detecting and imaging Cys in living nude mice, indicating its significant potential in biological applications.

It is important to detect hydrogen peroxide (H2O2) near mitochondrial DNA (mtDNA) because mtDNA is more prone to oxidative attack than nuclear DNA (nDNA). In this study, a mitochondria-targeted fluorescence probe, pep3-NP1, has been designed and synthesized. The probe contains a DNA-binding peptide, a H2O2 fluorescence reporter, and a positively charged red emissive styryl dye to facilitate accumulation in mitochondria. Due to groove binding of the peptide with DNA, the styryl dye of pep3-NP1 intercalated into the bases of DNA, leading to an increase in red fluorescence intensity (centered at 646 nm) and quantum yield. In this case, pep3-NP1 was a turn-on probe for labeling DNA. Subcellular locations of pep3-NP1 and MitoTracker suggested that pep3-NP1 mostly accumulated in the mitochondria of live cells. Namely, as an intracellular DNA marker, pep3-NP1 bound to mtDNA. In the presence of H2O2, pep3-NP1 emitted green fluorescence (centered at 555 nm). Thus, the ratio of green with red fluorescence of pep3-NP1 was suitable to reflect the change of the H2O2 level near mtDNA in living cells. The detecting limit for H2O2 was estimated at 2.9 and 5.0 μM in vitro and in cultured cells, respectively. The development of pep3-NP1 could help in studies to protect mtDNA from oxidative stress.

A ratiometric pH probe based on Tm3+ doped UCNPs functionalized with dye xylenol orange on the surface was developed, which can realize ratiometric pH sensing and imaging under continuous-wave excitation at 980 nm through the quenching and recovery of upconversion luminescence at 450 nm from UCNPs.

A kind of fluorescent/phosphorescent dual-emissive conjugated polyelectrolyte has been prepared by introducing phosphorescent platinum(II) porphyrin (O2-sensitive) into a fluorene-based conjugated polyelectrolyte (O2-insensitive), which can form ultrasmall conjugated polymer dots (FP-Pdots) in the phosphate buffer solution (PBS) via self-assembly caused by their amphiphilic structures with hydrophobic backbones and hydrophilic side chains. These FP-Pdots can exhibit an excellent ratiometric luminescence response to O2 content with high reliability and full reversibility for measuring oxygen levels, and the excellent intracellular ratiometric O2 sensing properties of the FP-Pdots nanoprobe have also been confirmed by the evident change in the Ired/Iblue ratio values in living cells cultured at different O2 concentrations. To confirm the reliability of the O2 sensing measurements of the FP-Pdots nanoprobe, O2 quenching experiments based on lifetime measurements of phosphorescence from Pt(II) porphyrin moieties have also been carried out. Utilizing the sensitivity of the long phosphorescence lifetime from Pt(II) porphyrins to oxygen, the FP-Pdots have been successfully applied in time-resolved luminescence imaging of intracellular O2 levels, including photoluminescence lifetime imaging and time-gated luminescence imaging, which will evidently improve the sensing sensitivity and reliability. Finally, in vivo oxygen sensing experiments were successfully performed by luminescence imaging of tumor hypoxia in nude mice.

It is well-known that the variation of noncovalent interactions of luminophores, such as π–π interaction, metal-to-metal interaction, and hydrogen-bonding interaction, can regulate their emission colors. Electrostatic interaction is also an important noncovalent interaction. However, very few examples of luminescence color tuning induced by electrostatic interaction were reported. Herein, a series of Zn(II)-bis(terpyridine) complexes (Zn-AcO, Zn-BF4, Zn-ClO4, and Zn-PF6) containing different anionic counterions were reported, which exhibit counterion-dependent emission colors from green-yellow to orange-red (549 to 622 nm) in CH2Cl2 solution. More importantly, it was found that the excited states of these Zn(II) complexes can be regulated by changing the electrostatic interaction between Zn2+ and counterions. On the basis of this controllable excited state, white light emission has been achieved by a single molecule, and a white light-emitting device has been fabricated. Moreover, a novel type of data dec...

A hybrid complex composed of an anionic conjugated polyelectrolyte (PFB-SO3Na) and a cationic phosphorescent Ir(III) oligomer is formed through electrostatic interaction by simple physical mixing in aqueous media. Due to their opposite charges and their effective spectral overlap, fluorescence resonance energy transfer occurs from the blue-emissive PFB-SO3Na to the red-emissive phosphorescent Ir(III) complex, which allows ratiometric and colorimetric Hg2+ sensing in aqueous solution with good selectivity, sensitivity, as well as visible detection. Time-resolved photoluminescence is applied for Hg2+ detection, which can effectively eliminate the background interference and improve the sensing sensitivity and signal-to-noise ratio in complicated media.

The application of a time-resolved photoluminescence technique and fluorescence lifetime imaging microscopy for biosensing and bioimaging based on phosphorescent conjugated polyelectrolytes (PCPEs) containing Ir(III) complexes and polyfluorene units is reported. The specially designed PCPEs form 50 nm nanoparticles with blue fluorescence in aqueous solutions. Electrostatic interaction between the nanoparticles and heparin improves the energy transfer between the polyfluorene units to Ir(III) complex, which lights up the red signal for naked-eye sensing. Good selectivity has been demonstrated for heparin sensing in aqueous solution and serum with quantification ranges of 0–70 μM and 0–5 μM, respectively. The signal-to-noise ratio can be further improved through time-resolved emission spectra, especially when the detection is conducted in complicated environment, e.g., in the presence of fluorescent dyes. In addition to heparin sensing, the PCPEs have also been used for specific labeling of live KB cell membrane with high contrast using both confocal fluorescent cellular imaging and fluorescence lifetime imaging microscopies. This study provides a new perspective for designing promising CPEs for biosensing and bioimaging applications.

A novel conjugated polymer, containing carbazole which acted as an electron-donor moiety, and a Pt(II) complex which acted as an electron-acceptor moiety, was synthesized and characterized. Electrical characterizations for the sandwiched polymer memory device (ITO/polymer/Al) indicate that the polymer possesses electrical bistability and the device exhibits resistive random-access memory. The memory mechanism has been investigated through theoretical calculations and attributed to the formation and dissociation of a charge-transfer state under the applied voltage. The device exhibits excellent memory performances, such as low threshold voltage, high ON/OFF current ratio, and good stability.

Gold nanoclusters (Au NCs) are promising luminescent nanomaterials due to their outstanding optical properties. However, their relatively low quantum yields and environment-dependent photoluminescence properties have limited their biological applications. To address these problems, we developed a novel strategy to prepare chitosan oligosaccharide lactate (Chi)-functionalized Au NCs (Au NCs@Chi), which exhibited emission with enhanced quantum yield and elongated emission lifetime as compared to the Au NCs, as well as exhibited environment-independent photoluminescence properties. In addition, utilizing the free amino groups of Chi onto Au NCs@Chi, we designed a FRET-based sensing platform for the detection of hydrogen sulfide (H2S). The Au NCs and the specific H2S-sensitive merocyanine compound were respectively employed as an energy donor and acceptor in the platform. The addition of H2S induced changes in the emission profile and luminescence lifetime of the platform with high sensitivity and selectivity. Utilization of the platform was demonstrated to detect exogenous and endogenous H2S in vitro and in vivo through wavelength-ratiometric and time-resolved luminescence imaging (TLI). Compared to previously reported luminescent molecules, the platform was less affected by experimental conditions and showed minimized autofluorescence interference and improved accuracy of detection.

As a marker for oxidative stress and a second messenger in signal transduction, hydrogen peroxide (H2O2) plays an important role in living systems. It is thus critical to monitor the changes in H2O2 in cells and tissues. Here, we developed a highly sensitive and versatile ratiometric H2O2 fluorescent probe (NP1) based on 1,8-naphthalimide and boric acid ester. In response to H2O2, the ratio of its fluorescent intensities at 555 and 403 nm changed 1020-fold within 200 min. The detecting limit of NP1 toward H2O2 is estimated as 0.17 μM. It was capable of imaging endogenous H2O2 generated in live RAW 264.7 macrophages as a cellular inflammation response, and especially, it was able to detect H2O2 produced as a signaling molecule in A431 human epidermoid carcinoma cells through stimulation by epidermal growth factor. This probe contains an azide group and thus has the potential to be linked to various molecules via the click reaction. After binding to a Nuclear Localization Signal peptide, the peptide-based combination probe (pep-NP1) was successfully targeted to nuclei and was capable of ratiometrically detecting nuclear H2O2 in living cells. These results indicated that NP1 was a highly sensitive ratiometric H2O2 dye with promising biological applications.

Smart luminescent materials that are responsive to external stimuli have received considerable interest. Here we report ionic iridium (III) complexes simultaneously exhibiting mechanochromic, vapochromic and electrochromic phosphorescence. These complexes share the same phosphorescent iridium (III) cation with a N-H moiety in the N^N ligand and contain different anions, including hexafluorophosphate, tetrafluoroborate, iodide, bromide and chloride. The anionic counterions cause a variation in the emission colours of the complexes from yellow to green by forming hydrogen bonds with the N-H proton. The electronic effect of the N-H moiety is sensitive towards mechanical grinding, solvent vapour and electric field, resulting in mechanochromic, vapochromic and electrochromic phosphorescence. On the basis of these findings, we construct a data-recording device and demonstrate data encryption and decryption via fluorescence lifetime imaging and time-gated luminescence imaging techniques. Our results suggest that rationally designed phosphorescent complexes may be promising candidates for advanced data recording and security protection.

Biothiols, such as cysteine (Cys) and homocysteine (Hcy), play very crucial roles in biological systems. Abnormal levels of these biothiols are often associated with many types of diseases. Therefore, the detection of Cys (or Hcy) is of great importance. In this work, we have synthesized an excellent "OFF-ON" phosphorescent chemodosimeter 1 for sensing Cys and Hcy with high selectivity and naked-eye detection based on an Ir(III) complex containing a 2,4-dinitrobenzenesulfonyl (DNBS) group within its ligand. The "OFF-ON" phosphorescent response can be assigned to the electron-transfer process from Ir(III) center and C^N ligands to the DNBS group as the strong electron-acceptor, which can quench the phosphorescence of probe 1 completely. The DNBS group can be cleaved by thiols of Cys or Hcy, and both the (3)MLCT and (3)LC states are responsible for the excited-state properties of the reaction product of probe 1 and Cys (or Hcy). Thus, the phosphorescence is switched on. Based on these results, a general principle for designing "OFF-ON" phosphorescent chemodosimeters based on heavy-metal complexes has been provided. Importantly, utilizing the long emission-lifetime of phosphorescence signal, the time-resolved luminescent assay of 1 in sensing Cys was realized successfully, which can eliminate the interference from the short-lived background fluorescence and improve the signal-to-noise ratio. As far as we know, this is the first report about the time-resolved luminescent detection of biothiols. Finally, probe 1 has been used successfully for bioimaging the changes of Cys/Hcy concentration in living cells.

In the present study, we explored a novel design strategy of heteronuclear phosphorescent iridium(III) complexes chelated by BF2 moiety with 3-hydroxypicolinic acid as the chelate ligand and synthesized a new series of iridium(III) complexes [Ir(dfppy)2(hpa)BF2] (1b), [Ir(ppy)2(hpa)BF2] (2b) and [Ir(tpq)2(hpa)BF2] (3b) (hpa = 3-hydroxypicolinic acid, dfppy = 2-(2,4-difluorophenyl)pyridine, ppy = 2-phenylpyridine, tpq = 2-(thiophen-2-yl)quinoline) under mild conditions. The emission colors and wavelengths of iridium(III) complexes can be affected evidently by chelating BF2 moiety into iridium(III) complexes, and this effect will be changed with the difference of cyclometalating CˆN ligands. A combination of UV-vis absorption, photoluminescence, excited-state lifetime measurements and theoretical calculations has provided the significant insight into the nature of the excited state and photophysical properties of these interesting iridium(III) complexes. Moreover, the exclusive staining of cytoplasm and low cytotoxicity were demonstrated for these new iridium(III) complexes, which made them promising candidates as multi-color phosphorescent dyes for living cell imaging.

With the emergence of phosphorescent heavy-metal complexes as a class of attractive probes for bioimaging, there is a parallel need to develop new phosphorescent probes with complete solubility in pure water for phosphorescent staining in living cells. Herein, a convenient and general design strategy for realizing phosphorescent heavy-metal complexes with complete water-solubility is provided and a series of cationic iridium(III) complexes [Ir(C^N)2(N^N)]+PF6− (C^N = 2-(2,4-difluorophenyl)pyridine (dfppy), 2-(4-(tert-butyl)phenyl)pyridine(t-buppy), 2-(thiophen-2-yl)quinoline) (thq), 4-(pyridin-2-yl)benzaldehyde (pba)) are prepared. The water-solubility of the complexes was successfully realized through the quaternization of the tertiary amino group in the N^N ligand. By changing the C^N ligands, the luminescent emission colors of these complexes can be tuned from green to red. These cationic iridium(III) complexes are membrane-permeable and can be applied as phosphorescent dyes for cell imaging in phosphate buffer solution (PBS). Complexes Ir1–Ir3 displayed specific staining of the cytoplasm and complex Ir4 containing two aldehyde groups could detect the changes of cysteine/homocysteine concentration in living cells. These results demonstrated that our design strategy offers an effective way to develop excellent phosphorescent cellular probes for real applications.