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Long-wavelength emission with high contrast toward species of interest is highly desired for fluorescence imaging in living objects. Herein, we proposed an exquisite enzyme-regulated "aggregation-induced emission (AIE) and intramolecular charge transfer (ICT)" strategy to optimize the signal-to-noise ratio for highly sensitive detection of enzymes. Benefiting from the synergistic effect, probes ABT-Gal-1 and ABT-Gal-2 exhibited faint background signals but dramatically enhanced near-infrared fluorescence upon exposure toward β-galactosidase (β-gal). Notably, both probes could be accessible in aqueous media. Preferably, the fluorescence intensity of ABT-Gal-1 exhibited a satisfactory linear relationship in the wide concentration range of 0.5–30 U/L with a very low detection limit to 0.24 U/L. Further, by monitoring endogenous β-gal in ovarian cancer cells, a precious merit of resistance to multiple washes was identified, which was facilitated by the nanoaggregate formation in situ upon activation. This work proposes a guiding strategy for manipulating various lighting mechanisms to develop attractive probes and, equally importantly, it provides an ideal practical tool for elucidating the biological role of β-gal in biological scenarios. [Display omitted] • Comprehensive insights into the ICT and AIE characteristic of amino-type ESIPT-based fluorophore are proposed. • An exquisite enzyme-regulated "AIE and ICT" strategy to optimize the signal-to-noise ratio is reported for the first time. • Debut of activatable AIE probe for β-gal with emission in near-infrared window is well presented. • Probe ABT-Gal-1 was allowed in aqueous media with the lowest detection limit (0.24 U/L) compared with reported probes. • The nanoaggregation-allowed probe was firstly disclosed with resistance to multiple washes during cell imaging. [ABSTRACT FROM AUTHOR]

Mitochondrial viscosity and ONOO− are involved in various pathological and physiological processes. Abnormal viscosity or irregular ONOO− concentration would disrupt the normal function of cells. Hence, we skillfully designed and synthesized a dual-responsive probe Mito-HC-TZ for the simultaneous detection of ONOO− and viscosity by different channels. 3-ethylbenzothiazolium was acted as fluorescent rotor to regulate the twisted intramolecular charge transfer (TICT) process; the C = C of 3-ethylbenzothiazolium linked to the xanthene core could be easily broken by ONOO−. Thus, the probe responded to viscosity and ONOO− by red and orange fluorescence channels, respectively. Mito-HC-TZ had high selectivity, low cytotoxicity and wide range of pH values. The results of cell imaging experiments showed the probe could be used to respectively monitor the viscosity and ONOO− level in HepG2 cells. [Display omitted] • A NIR probe for viscosity and ONOO− according to two channels was developed. • Mito-HC-TZ could ratiometrically respond to mitochondrial viscosity and ONOO−. • Mito-HC-TZ was applied to detect the changes of viscosity and ONOO− in cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • BODIPY derivatives with triarylamine (TPA) moieties on their 3-, 5-, or 8-positions showed near infrared emission, large Stokes shifts and two-photon absorptions. • These triarylamine (TPA) modified BODIPYs showed aggregation-induced emission (AIE) properties. • These BODIPYs all can be used in tracking the dynamic behaviors of lipid droplets or lysosomes in living cells. A series of five BODIPY derivatives with triarylamine (TPA) moieties on their 3-, 5-, or 8-positions were reported, which showed wide-range fluorescence emissions across red and near infrared regions in their aggregation states. The influences of numbers and substituted positions of TPA groups on the optical and aggregation-induced emission (AIE) properties of these BODIPYs as well as organelle-specific imaging in live cells were investigated. The TPA groups installed at 3-/5-positions of BODIPY could effectively enlarge the conjugated system and red-shift the absorption and emission bands (λ em max up to 815 nm). In contrast, the TPA group linked to 8-position of BODIPY core has little contribution to decrease the HOMO-LUMO energy gap. Importantly, regardless the substitution positions of TPA groups, all these TPA-substituted BODIPYs (BTs) showed remarkable AIE performance and possessed high molar extinction absorption (up to ∼ 63000 M−1 cm−1), two-photon absorption (up to 171 GM at 870 nm), and large Stokes shifts. The BODIPY with one TPA group (BT1 and FBT1) showed lipid droplets-specific localization while BODIPY with two and three TPA groups (BT2 , BT3 and FBT2) preferred to enrich in lysosomes. These BODIPYs all have been successfully used in tracking the dynamic behaviors of lipid droplets or lysosomes in living cells. Furthermore, BT1 and FBT1 can quantitatively detect the overexpression of lipid droplets, and BT3 has been successfully used to observe lysosomes behaviors of lipophagy process in living cells. This work systematically studied the influence of the number and position of TPA units on the optical properties and AIE-activities of BODIPYs, which not only enriched the BODIPY-based AIE NIR probes for organelle-specific imaging in live cells, but also provided a practical strategy for the effective construction of organic dyes with NIR AIE activity. [ABSTRACT FROM AUTHOR]

A fluorescent probe, 1,4-diethyl-7-(3-pyridin-2-yl-acroyloyl)-1,2,3,4-tetrahydro-5-oxa-1,4-diazaanthracen-6-one (probe 1 ), with an emission in near-infrared region was developed for sensitive and selective detection of biothiols. Probe 1 is essentially non-fluorescent due to the strong intramolecular charge transfer (ICT) from the electron-donating tetrahydroquinoxaline moiety to the electron-withdrawing pyridine group. Upon the treatment with biothiols, the conjugation system was broken via Michael addition reaction between biothiols and α,β-unsaturated ketone, which inhibited the ICT process and resulted in a remarkable fluorescence enhancement with an emission maximum at 660 nm. Moreover, probe 1 was successfully applied to image intracellular thiols in living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Near-infrared Turn-on Fluorescent probe has been synthesized. • Fast response to Selenocysteine with a large turn-on Near-infrared fluorescence signal. • Low detection limit, high selectivity and sensitivity. • Capability for identification of Sec in living cells and mice. Selenocysteine (Sec) plays critical roles in many physiological and pathological processes of human beings, thus it is of great significance to develop accurate methods for detecting and visualizing Sec. Herein, a new anthracene derivative (YZ-M5) as a near-infrared (NIR) fluorescent probe for sensing Sec was designed. Based on the target-induced modulation of the intramolecular charge transfer (ICT) process of the probe, YZ-M5 can display a rapid strong NIR fluorescence enhancement at 660 nm for Sec within 5 min. The quantitative detection range for Sec is 0–40 μM with a low detection limit of 18.5 nM. YZ-M5 also showed high selectivity and sensitivity, as well as the capability for identification of Sec in living cells and mice. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) emitting functional dyes have been attracting considerable attention because they are useful in the fields of cellular imaging, security application, energy conversion, and so on. In this study, to develop NIR fluorescent dyes with high photoluminescence (PL) quantum yields (Φ PL), novel acceptor–donor–acceptor (A–D–A) type π-conjugated molecules have been prepared, where dimeric dithienosilole (DTS) and freebase or quaternized 1-pyridylacryronitrile are involved as the D and A moieties, respectively. The freebase dye exhibited red fluorescent emission at 654 nm with Φ PL of 0.10 in dichloromethane at rt, whereas the methylation of the pyridine moieties at the molecular termini led to a significant red shift of the emission to the NIR region (PL maximum λ PL ; 822 nm), accompanied by improvement of a high Φ PL of 0.20 in dichloromethane at rt. The results of density functional theory (DFT) and time-dependent DFT calculations indicated that the considerable red shift of the emission band of the quaternized dye originates from effective intramolecular charge transfer from the DTS donor to the terminal pyridiniums and that the high value of Φ PL is brought about by minimal structural relaxation upon photoexcitation. NIR emission was also obtained when the freebase dye was placed under acidic conditions: protonation at the Lewis basic pyridine moieties brought about halochromic response of PL to yield red-shifted emission (λ PL ; 755 nm), when trifluoroacetic acid was added to the dichloromethane solution. Image 1 • A–D–A type fluorescent dithienosilole dimers with terminal pyridines were prepared. • Quaternization of the pyridine moieties led to red shifts of UV–vis and PL spectra. • The quaternized A–D–A dye exhibited intense near-infrared fluorescence. • The quaternized A–D–A dye adopted a highly planar structure at the excited state. • The freebase A–D–A dye showed near-infrared fluorescence under acidic conditions. [ABSTRACT FROM AUTHOR]

• A simple near-infrared fluorescence probe based on dicyanoisophorone was synthesized. • This probe exhibited excellent specificity in the detection of N 2 H 4 over other amino compounds. • This probe showed excellent response performance to N 2 H 4 through distinct fluorescence enhancement. • This probe was applicable for N 2 H 4 detection in living cells and real water samples. With the widespread use of N 2 H 4 , it brings potential risks to human health. In order to determine N 2 H 4 effectively in both environment and living systems, a simple near-infrared fluorescence probe was prepared for the specific response of N 2 H 4 based on the intramolecular charge transfer (ICT) mechanism. This probe provided a "turn on" fluorescence response to N 2 H 4 with characteristics including high selectivity, rapid response (within 1 min), low cytotoxicity, and low detection limit (0.022 μM). In addition, it can be used to expediently trace N 2 H 4 in HepG2 cells and water samples. Thus, Probe 1 is a promising tool to identify the level of N 2 H 4. [ABSTRACT FROM AUTHOR]

Hypobromous acid (HOBr) is an important reactive oxygen species and has been recently found to be associated with a variety of diseases. However, owing to a lack of effective analytical tools, there is still limited understanding of its roles in living systems. Here, we present a new type of near-infrared fluorescent probe DCSN for HOBr detection. The designed probe exhibits high sensitivity with a low detection limit, excellent selectivity over other interfering species and low cytotoxicity. More interestingly, the fluorescence response behavior of the probe was different from the previous literatures due to the intramolecular charge transfer process. Moreover, we have successfully monitored HOBr in living cells by utilizing DCSN. This probe has potential to be used as a promising tool for better understanding the physiological functions of HOBr. Unlabelled Image • A dicyanomethylene benzopyran based near-infrared fluorescent probe DCSN for efficient detection of HOBr was designed • The fluorescence response behavior of DCSN was different from the previous literatures due to-ICT process • Cell imaging experiments demonstrated that DCSN could be employed to image HOBr in living cells [ABSTRACT FROM AUTHOR]