Development of an intramolecular charge transfer-type colorimetric and fluorescence sensor for water by fusion with a juloidine structure and complexation with boron trifluoride

Advances on fluorescence chemosensors for selective detection of water

Water, although an important part of everyday life, is acts as one of the most significant contaminants in various applications such as biomedical monitoring, chemical production, petroleum-based fuel and food processing. In fact, the presence of water in other solvents is a huge concern. For the quantification of trace water content, different methods such as Karl-Fischer, electrochemical, nuclear magnetic resonance, chromatography, and thermogravimetric analysis have been used. Although every technique has its own benefit, each one suffers from several drawbacks that include high detection costs, lengthy procedures and specialized operations. Nowadays, the development of fluorescence-based chemical probes has become an exciting area of research for the quick and accurate estimation of water content in organic solvents. A variety of chemical processes such as hydrolysis reaction, metal ions promoted oxidation reaction, suppression of the -C═N isomerization, protonation and deprotonation reactions, and molecular aggregation have been well researched in the last few years for the fluorescent detection of trace water. These chemical processes eventually lead to different photophysical events such as aggregation-induced emission (AIE), aggregation-induced emission enhancement (AIEE), aggregation-caused quenching (ACQ), fluorescent resonance energy transfer (FRET), charge transfer, photo-induced electron transfer (PET), excited state intramolecular proton transfer (ESIPT) that are responsible for the detection. This review presents a summary of the fluorescence-based chemosensors reported in recent years. The design of water sensors, sensing mechanisms and their potential applications are reviewed and discussed.

The catalyst free synthesis of dibenzo[a,j]acridine and its applications in bioimaging of BF3 in HeLa cells

In this paper, we discuss how tetrahydrodibenzo[a,j]acridine (4-HA) loses its hydrogen, which makes dibenzo[a,j]acridine (ARM) and also how 4-HA can be synthesized effectively using 2-tetralone in high yield. Dehydrogenative condensation and dehydrogenation are the two processes that make up the overall reaction of this synthetic approach. In addition, the presence of BF3 caused a remarkable fluorescence shift in ARM. Test paper analysis was used for examining the practical usefulness of ARM, which can be seen under UV light, resulting in this unique phenomenon. The fluorescent bio imaging experiment demonstrates that the sensor ARM has the capability to detect BF3 in living HeLa cells.

A tert-Butyldiphenylsilyl-Containing Polyimide-Based Chemosensor for Sequential Detection of Fluoride Ions and Trace Water in Organic Solvents

A tert-butyldiphenylsilyl-containing polyimide (PI-OSi) has been established as a colorimetric and ratiometric chemosensor for rapid detecting fluoride ions (F-). The UV-vis absorbance ratio value (A322/A288) of PI-OSi in a DMF solution displays a wide linear range change to F- concentrations with a detection limit (DL) value of 2.13 μM. Additionally, adding incremental amounts of F- to a DMF solution of PI-OSi shows an immediate color change to yellow and finally to green from colorless. More interestingly, the resulting PI-OSi plus F- system (PI-OSi·F) could detect trace water in DMF. The A292/A322 value of PI-OSi·F almost linearly increases with low water content, which suggests convenient quantitative sensing of trace water content in DMF. The DL value of PI-OSi·F for sensing water in DMF is determined to be 0.00149% (v/v). The solution color of PI-OSi·F returns to colorless when the water content increases, indicating that PI-OSi·F can conveniently estimate water content in DMF by naked-eye detection. The detection mechanisms confirmed by an 1H NMR study and a DFT calculation involve a F--induced desilylation reaction of PI-OSi to form phenolate anion followed by protonation with trace water. Finally, PI-OSi film was fabricated for the colorimetric detection of F- and water in CH3CN.

Novel pH-activatable NIR fluorogenic spray mediated near-instant and precise tumor margins identification in human cancer tissues for surgical resection

Rationale: Challenges such as developing a universal tumor-specific probe for tumor margin identification in diverse tumors with an easy-operative and fast-imaging pattern still exist. Hence, in the present study, a rapidly "off-on" near-infrared (NIR) fluorescent probe NBD with pH-activatable fluorescence and a large Stokes shift was constructed for spray mediated near-instant and precise clinical tumor margins identification. Methods: NBD was designed and synthesized by introducing both diphenyl amino group and benzo[e]indolium to β-carboline at C-6 and C-3 positions respectively. The optical properties of NBD was characterized by absorption spectra, fluorescence spectra. Subsequently, we investigated its pH-dependent mechanism by 1H NMR and density functional theory (DFT) calculation. NBD was further under deeper investigation into its imaging performance in nude mice models (subcutaneous, orthotopic, metastatic tumor), and clinical tissues from patients with three clinically representative tumors (liver cancer, colon cancer, and lung cancer). Results: It was found that NBD had NIR fluorescence (742 nm), a large Stokes shift (160 nm), and two-photon absorbance (1040 nm). Fluorescence quantum yield (ФF) increased by 5.5-fold when pH decreased from 7.4 to 4.0, to show pH-dependent property. Furthermore, NBD could not only selectively light up all four cancer cell lines, but also delineate xenograft tumor and orthotopic microtumor to guide surgical tumor resection, and track metastatic tissues. Particularly, after simple topical spray (three minutes later), NBD could rapidly and precisely distinguish the boundary ranges of three kinds of clinical cancer specimens including liver, colon, and lung cancers, with high tumor-to-normal tissue signal ratios (6.48~9.80). Conclusions: Therefore, the proposed fluorescent probe NBD may serve as a versatile NIR fluorogenic spray for the near-instant visualization of tumor margins and assisting surgeons in surgerical resection of clinical cancers.

Fluorescence Sensor for Water in Organic Solvent Using Graphene Oxide- Rhodamine B and Cucurbit[7]uril

Detection of water in organic solvents gained much importance as these solvents have been used as a medium for conducting organic reactions and water was considered as an inhibitor, when it is present in the reaction medium. There are number of methods available to measure the water content in organic solvents, however, such methods are time consuming and expensive. Here, we developed a facile method for detecting water in organic solvents using an inexpensive fluorescent probe - Rhodamine B decorated Graphene oxide (RBGO). The fluorescent probe, RBGO can be conveniently prepared by mixing the rhodamine B (RB) with graphene oxide (GO) in water. However, the probe will function as a sensor for water in the organic solvents through the release of dye upon interaction with the water present in organic solvents. Surprisingly, combination of cucurbit[7]uril (CB[7]) and RBGO increased the sensitivity of this sensor dramatically for the detection of water. This is the first example of water sensor with best detection limit by the involvement of host molecules such as CB[7]. This sensor displayed the low limit of detection (LOD) for organic solvents (LOD: 0.0015% for DMSO, 0.0025% for DMF), through the two-way process such as decomplexation and encapsulation. We presume that the role of CB [7] can be implemented in other similar sensors to enhance the sensitivity.

Development of a NIR iridium(III) complex for self-calibrated and luminogenic detection of boron trifluoride

Boron trifluoride (BF3) is a potential environmental pollutant, and excess exposure to it may cause human diseases. However, the sensitive, rapid and accurate detection of BF3 for on-site purposes is still a challenge. In this work, we developed the first NIR iridium(III)-based probe with dual emission and a Stokes shift of 370 nm for self-calibrated and luminogenic detection of BF3. This probe exhibited a strong luminescence enhancement at around 650 nm to BF3 (0-100 μM) with almost no change in luminescence at 475 nm, displaying a 220-fold I650 nm/I475 nm enhancement at 100 μM of BF3 with a detection limit of 0.35 μM. Moreover, the probe showed a fast response time of less than 5 s to BF3 along with an obvious color change under UV irradiation for visual detection. Importantly, the desirable photophysical properties of the iridium(III)-based probe can be harnessed for time-resolved detection of BF3 in the presence of the fluorescence background. The applicability of the probe was further verified in an organic solvent waste-spiked system and on a glass pane. This work will provide a solid basis for the development of sensitive and on-site BF3 sensing toolkits for environmental monitoring.

Lithium sensors based on photophysical changes of 1-aza-12-crown-4 naphthalene derivatives synthesized via Buchwald-Hartwig amination

Lithium detection is of great significance in many applications. Lithium-sensing compounds with high selectivity are scarce and, if any, complicated to synthesize. We herein report a novel yet simple compound that can detect lithium ions in an organic solvent through changes in absorbance and fluorescence. Naphthalene functionalized with 1-aza-12-crown-4 (1) was synthesized via one step from commercially available 1-bromonaphthalene through Buchwald-Hartwig amination. In order to obtain a structure-property relationship, we also synthesized two other compounds that are structurally similar to 1, wherein the compounds 2 and 3 include an imide moiety (an electron acceptor) and do not include a 1-aza-12-crown-4 unit, respectively. Upon the addition of lithium ions, compound 1 displayed a clear isosbestic point in the absorption spectra and a new peak in the fluorescence spectra, whereas the compounds 2 and 3 indicated miniscule and no spectroscopic changes, respectively. 1H NMR titration studies and the calculated optimized geometry from density functional theory (DFT) indicated the lithium binding on the aza-crown. The calculated limit of detection (LOD) was 21 μM. The lithium detection with 1 is selective among other alkali metals (Na+, K+, and Cs+). DFT calculation indicated that the lone pair electrons in the nitrogen atom of 1 is delocalized yet available to bind lithium, whereas the nitrogen lone pair electrons of 2 showed significant intramolecular charge transfer to the imide acceptor, resulting in a high dipole moment, and thus were unavailable to bind lithium. This work elucidates the key design parameters for future lithium sensors.

Tetraphenylethene–anthracene-based fluorescence emission sensor for detection of water with photo-induced electron transfer and aggregation-induced emission characteristics

As a fluorescent sensor for water over a wide range from low to high water content regions in organic solvents, we have designed and developed a PET (photo-induced electron transfer)/AIE...

Fluorescent polymer films based on photo-induced electron transfer for visualizing water

As fluorescent materials for visualization, detection, and quantification of a trace amount of water, we have designed and developed a PET (photo-induced electron transfer)-type fluorescent monomer SM-2 composed of methyl methacrylate-substituted anthracene fluorophore-(aminomethyl)-4-cyanophenylboronic acid pinacol ester (AminoMeCNPhenylBPin) and achieved preparation of a copolymer poly(SM-2-co-MMA) composed of SM-2 and methyl methacrylate (MMA). Both SM-2 and poly(SM-2-co-MMA) exhibited enhancement of the fluorescence emission with the increase in water content in various solvents (less polar, polar, protic, and aprotic solvents) due to the formation of the PET inactive (fluorescent) species SM-2a and poly(SM-2-co-MMA)a, respectively, by the interaction with water molecules. The detection limit (DL) of poly(SM-2-co-MMA) for water in the low water content region below 1.0 wt% in acetonitrile was 0.066 wt%, indicating that poly(SM-2-co-MMA) can act as a PET-type fluorescent polymeric sensor for a trace amount of water in solvents, although it was inferior to that (0.009 wt%) of SM-2. It was found that spin-coated poly(SM-2-co-MMA) films as well as 15 wt% SM-2-doped polymethyl methacrylate (PMMA) films produced a satisfactory reversible fluorescence off–on switching between the PET active state under a drying process and the PET inactive state upon exposure to moisture, which is demonstrated by the fact that the both the films are similar in hydrophilicity to each other from the measurement of the water contact angles on the polymer film surface. Herein we propose that PET-type fluorescent polymer films based on a fluorescence enhancement system are one of the most promising and convenient functional dye materials for visualizing moisture and water droplets.

Photo-induced electron transfer (PET)-type fluorescent polymer films based on a fluorescence enhancement system have been prepared as one of the most promising and convenient functional dye materials for visualizing moisture and water droplets.

An ethanethioate functionalized polythiophene as an optical probe for sensitive and fast detection of water content in organic solvents

A new polythiophene-based optical probe, namely PTS, was designed and prepared for detection and quantification of the water present in organic solvents. PTS exhibited sensitive and fast absorption and fluorescence signaling response to the changes of water content in tetrahydrofuran (THF), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc) due to the water-induced interpolymer-stacking aggregation as demonstrated by dynamic light scattering (DLS) analysis. The fluorescence intensity of PTS at 550 nm linearly reduced as a function of the water content in detection ranges of 0-30% (v/v) in THF, 0-10% in DMF and 0-10% in DMAc with the limit of detection (LOD) for water being 0.034% (v/v) in THF, 0.013% (v/v) in DMF, and 0.014% (v/v) in DMAc, respectively. Additionally, PTS-incorporated test paper was fabricated to successfully achieve naked-eye detection of water in DMF and DMAc. PTS was further applied to estimate the water content in real samples, convincingly demonstrating that our method was comparable with the standard Karl Fischer titration.

Polymer films doped with fluorescent sensor for moisture and water droplet based on photo-induced electron transfer

Anthracene-(aminomethyl)phenylboronic acid pinacol ester (AminoMePhenylBPin) OF-2 acts as a PET (photo-induced electron transfer)-type fluorescent sensor for determination of a trace amount of water: the addition of water to organic solvents containing OF-2 causes a drastic and linear enhancement of fluorescence emission as a function of water content, which is attributed to the suppression of PET. Indeed, detection limits (DLs) for OF-2 were as low as 0.01–0.008 wt% of water in solvents, that is, the PET method makes it possible to visualize, detect, and determine a trace amount of water. Thus, in this work, in order to develop fluorescent polymeric materials for visualization and detection of water, we have achieved the preparation of various types of polymer films (polystyrene (PS), poly(4-vinylphenol) (PVP), polyvinyl alcohol (PVA), and polyethylene glycol (PEG)) which were doped with OF-2, and investigated the optical sensing properties of the OF-2-doped polymer films for water. As-prepared OF-2-doped polymer films initially exhibited green excimer emission in the PET active state, but blue monomer emission in the PET inactive state upon exposure to moisture or by water droplet. Moreover, it was found that the OF-2-doped polymer films show the reversible fluorescence properties in the dry–wet process. Herein we propose that polymer films doped with PET-type fluorescent sensors for water based on a fluorescence enhancement (turn-on) system are one of the most promising and convenient functional materials for visualizing moisture and water droplets.

Polymer films doped with a photo-induced electron transfer (PET)-type fluorescent sensor exhibit green excimer emission in the PET active state, but blue monomer emission in the PET inactive state upon exposure to moisture.

Fluorescence sensors for detection of water based on tetraphenylethene–anthracene possessing both solvatofluorochromic properties and aggregation-induced emission (AIE) characteristics

TPE-(An-CHO)4 has been developed as an SFC (solvatofluorochromism)/AIEE (aggregation-induced emission enhancement)-based fluorescence sensor for detection of water over a wide range from low to high water content regions in solvents.

Naked eye detection of moisture in organic solvents and development of alginate polymer beads and test cassettes as a portable kit

New dabsyl-thiophene based receptor DABT and its mercury complex DABT-Hg is reported as a colorimetric sensor for rapid and sensitive detection of trace amount of water in aprotic solvents. Based on intramolecular charge transfer in the excited state, the receptor dabsyl-thiophene (yellow color) binds with the mercury ions (magenta color) to stimulate a colorimetric response. The mercury complex is used as a moisture sensor in THF, acetone, and acetonitrile due to its instability in moisture containing organic solvents. The probe exhibits higher sensitivity towards water in THF (LOD = 0.0041% w/w), acetone (LOD = 0.0144% w/w) and acetonitrile (LOD = 0.1008% w/w). The dissociation of mercury from probe DABT-Hg in the presence of water is accountable for the colorimetric response as proven by the ¹H NMR and ESI-MS studies. DABT-Hg is the first mercury based complex for the detection of moisture in organic solvents. Test paper strip and PVA thin film doped with the probe were successfully used to detect moisture content in organic solvents. DABT-Hg incorporated alginate beads are prepared to determine the water content in triethylamine and ethylene glycol. Portable test cassettes are developed for the on-site detection of distilled and undistilled wet solvents in the chemical laboratory through naked-eye detection.

Development of optical sensor for water in acetonitrile based on propeller-structured BODIPY-type pyridine-boron trifluoride complex

A propeller-structured 3,5,8-trithienyl-BODIPY-type pyridine–boron trifluoride complex, ST-3-BF₃, which has three units of 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile at the 3-, 5-, and 8-positions on the BODIPY skeleton, was designed and developed as an intramolecular charge transfer (ICT)-type optical sensor for the detection of a trace amount of water in acetonitrile. The characterization of ST-3-BF₃ was successfully determined by FTIR, ¹H and ¹¹B NMR measurements, high-resolution mass spectrometry (HRMS) analysis, thermogravimetry-differential thermal analysis (TG-DTA), photoabsorption and fluorescence spectral measurements, and density functional theory (DFT) calculations. ST-3-BF₃ showed a broad photoabsorption band in the range of 600 to 800 nm, which is assigned to the S₀ → S₁ transition of the BODIPY skeleton with the expanded π-conjugated system over the 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile units at the 3-, 5-, and 8-positions onto the BODIPY core. In addition, a photoabsorption band was also observed in the range of 300 to 550 nm, which can be assigned to the ICT band between the 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile units at 3-, 5-, and 8-positions and the BODIPY core. ST-3-BF₃ exhibited a characteristic fluorescence band originating from the BODIPY skeleton at around 730 nm. It was found that by addition of a trace amount of water to the acetonitrile solution of ST-3-BF₃, the photoabsorption band at around 415 nm and the fluorescence band at around 730 nm increased linearly as a function of the water content below only 0.2 wt%, which could be ascribed to the change in the ICT characteristics due to the dissociation of ST-3-BF₃ into ST-3 by water molecules. Thus, this work demonstrated that the 3,5,8-trithienyl-BODIPY-type pyridine–boron trifluoride complex can act as a highly-sensitive optical sensor for the detection of a trace amount of water in acetonitrile.

Propeller-structured 3,5,8-trithienyl-BODIPY-type pyridine–boron trifluoride complex, ST-3-BF₃, has been developed as an intramolecular charge transfer (ICT)-type optical sensor for the detection of a trace amount of water in acetonitrile.