Fluorescent and colorimetric detection of acid vapors by using solid-supported rhodamine hydrazides

A Facile Fabrication of Lysosome-Targeting pH Fluorescent Nanosensor Based on PEGylated Polyester Block Copolymer

A novel lysosome-targeting PEGylated polyester-based fluorescent pH nanosensor is fabricated by the combination of ring-opening copolymerization (ROCOP), side-group modification and subsequent self-assembly. First, a key target amphiphilic copolymer carrier for rhodamine (Rh) pH indicator is synthesized in a facile manner by the ROCOP of phthalic anhydride with allyl glycidyl ether using mPEG-OH and t-BuP1/Et3B as the macroinitiator and binary catalyst, respectively. Subsequently, Rh moieties are covalently attached on the polymer chain with controllable grafting degree via an efficient thiol-ene click reaction. Concurrently, the effect of catalyst systems and reaction conditions on the catalytic copolymerization performance is presented, and the quantitative introduction of Rh is described in detail. Owing to its amphiphilic characteristics, the rhodamine-functionalized polyester-based block copolymer can self-assemble into micelles. With the covalent incorporation of Rh moieties, the as-formed micelles exhibit excellent absorption and fluorescence-responsive sensitivity and selectivity towards H+ in the presence of various metal cations. Moreover, the as-prepared micelles with favorable water dispersibility, good pH sensitivity and excellent biocompatibility also display appreciable cell-membrane permeability, staining ability and pH detection capability for lysosomes in living cells. This work provides a new strategy for the facile synthesis of novel biocompatible polymeric fluorescent pH nanosensors for the fluorescence imaging of lysosomal pH changes.

Rhodamine phenol-based fluorescent probe for the visual detection of GB and its simulant DCP

Rhodamine phenol-based fluorescent probes have been synthesized. The probe RBNP demonstrates a rapid response and extreme low limit detection to diethylchlorophosphate and can rapidly and visually detect a real nerve agent GB in vapor.

Highly fluorescent triazolopyridine-thiophene D-A-D oligomers for efficient pH sensing both in solution and in the solid state

Conjugated fluorophores have been extensively used for fluorescence sensing of various substances in the field of life processes and environmental science, due to their noninvasiveness, sensitivity, simplicity and rapidity. Most existing conjugated fluorophores exhibit excellent light-emitting performance in dilute solutions, but their properties substantially decrease or even completely vanish due to severe aggregation quenching in the solid state. Herein, we synthesize a series of triazolopyridine-thiophene donor-acceptor-donor (D-A-D) type conjugated molecules with high absolute fluorescence quantum yields (ΦF) ranging from 80% to 89% in solution. These molecules also show unusual light-emitting properties in the solid state with ΦF of up to 26%. We find that owing to the protonation-deprotonation process of the pyridine ring, these compounds display obvious changes in both fluorescence wavelength and intensity upon addition of acids, and these changes can be readily recovered by the successive introduction of bases. By harnessing this phenomenon, we further show that these fluorophores can be employed for efficient and reversible fluorescence sensing of hydrogen ions in a broad pH range (0.0-7.0). With the fabrication of pH testing papers and ink-printed complex patterns including butterflies and letters on substrates, we demonstrate the application of such sensors to fluorescence indication or solid state pH detection for real samples such as volatile acidic/basic gas and water-quality analysis.

New Six-Membered pH-Insensitive Rhodamine Spirocycle in Selective Sensing of Cu2+ through C-C Bond Cleavage and Its Application in Cell Imaging

A new rhodamine-based chemosensor 1 with a six-membered spirocyclic ring has been synthesized, which exhibits excellent pH stability and shows selective "turn-on" fluorescent detection of Cu²⁺ ions over a series of other metal ions including Cu⁺ ions. The expansion of spirocycle improves the stability and selectivity of the chemosensors in sensing of metal ions. Till today only few rhodamine structures R1-R5 with thiourea-, hydrazine amide-, or pyrrole-decorated six-membered spirocyclic rings are known that exhibit metal-ion sensing via C-N bond cleavage of the spiro ring. In this context, rhodamine compound that responds to the metal ion through C-C bond cleavage of the six-membered spiro ring is completely unknown. The present example is a first-time report that demonstrates selective sensing of Cu²⁺ ions through C-C bond cleavage over the conventional existing systems in the literature. The chemosensor 1 is cell permeable and can detect Cu²⁺ in live cells using confocal microscopy in the biologically relevant pH range with high photostability.

Light-Up of Rhodamine Hydrazide to Generate Emissive Initiator for Polymerization and to Afford Photochromic Polypeptide Metal Complex

Ring-opening polymerization (ROP) of cyclic peptide monomer of γ-propargyl-l-glutamate N-carboxyanhydride (PLG⁻NCA) was originally initiated by non-emissive, ring-close rhodamine 6G hydrazide (R-C). However, instantaneously after adding PLG⁻NCA to R-C, the spirolactam ring of R-C was opened by PLG⁻NCA, rendering emissive, ring-open R-O to initiate ROP of PLG⁻NCA. The emissive R-O moiety therefore produced fluorescent R⁻PLG with aggregation-induced emission (AIE) properties. Moreover, R⁻PLG was found to exhibit photochromic properties with good fatigue resistance and long lifetime when forming metal complexes with Sn(II) and Fe(III). In the dark, irradiated metal complexes slowly (~50 min) restored to the initial state. This research provides foundation for the development of new photochromic materials with long lifetime.

A Novel Mechanochromic and Photochromic Polymer Film: When Rhodamine Joins Polyurethane

A rhodamine-based molecule, Rh-OH, is synthesized. Rh-OH exhibits a reversible mechanochromic luminescent character but a passivating response to UV light. An elastomeric polymer film based on polyurethane with embedded Rh-OH is prepared via a polycondensation reaction. The film shows mechanochromic and photochromic properties with reversible color change, which originates from the isomerization of the Rh-OH molecule from a twisted spirolactam in the ring-closed form to a planarized zwitterionic structure in the ring-open state.

A selectively fluorescein-based colorimetric probe for detecting copper(II) ion

A novel fluorescein derivative 3-bromo-5-methylsalicylaldehyde fluorescein hydrazone (BMSFH) has been synthesized by reacting fluorescein hydrazide with 3-bromo-5-methylsalicylaldehyde and was developed as a new colorimetric probe for detection of Cu(2+). In the presence of Cu(2+) the BMSFH exhibits a rapid color change from colorless to yellow together with an obvious new band appeared at 502nm in the UV-vis absorption spectra. However, other common alkali-, alkaline earth-, transition- and rare earth metal ions induced no or minimal spectral changes. This change is attributed to BMSFH via coordination with Cu(2+) in a 1:1 stoichiometry and this binding to Cu(2+) is reversible, as indicated by the bleaching of the color when the Cu(2+) is extracted with EDTA. Experimental results indicate that the BMSFH can provide a rapid, selective and sensitive response to Cu(2+) with a linear dynamic range 3.0-330μmol/L and can be used as a potential Cu(2+) colorimetric probe in aqueous solution.

A Highly Selective and Sensitive Turn-On Fluorescent Chemosensor Based on Rhodamine 6G for Iron(III)

Recently, more and more rhodamine derivatives have been used as fluorophores to construct sensors due to their excellent spectroscopic properties. A rhodamine-based fluorescent and colorimetric Fe(3+) chemosensor 3',6'-bis(ethylamino)-2-acetoxyl-2',7'-dimethyl-spiro[1H-isoindole-1,9'-[9H]xanthen]-3(2H)-one (RAE) was designed and synthesized. Upon the addition of Fe(3+), the dramatic enhancement of both fluorescence and absorbance intensity, as well as the color change of the solution, could be observed. The detection limit of RAE for Fe(3+) was around 7.98 ppb. Common coexistent metal ions showed little or no interference in the detection of Fe(3+). Moreover, the addition of CN(-) could quench the fluorescence of the acetonitrile solution of RAE and Fe(3+), indicating the regeneration of the chemosensor RAE. The robust nature of the sensor was shown by the detection of Fe(3+) even after repeated rounds of quenching. As iron is a ubiquitous metal in cells and plays vital roles in many biological processes, this chemosensor could be developed to have applications in biological studies.

A selectively rhodamine-based colorimetric probe for detecting copper(II) ion

A novel rhodamine derivative 3-bromo-5-methylsalicylaldehyde rhodamine B hydrazone (BMSRH) has been synthesized by reacting rhodamine B hydrazide with 3-bromo-5-methylsalicylaldehyde and developed as a new colorimetric probe for the selective and sensitive detection of Cu2+. Addition of Cu2+ to the solution of BMSRH results in a rapid color change from colorless to red together with an obvious new band appeared at 552 nm in the UV-vis absorption spectra. This change is attributed to the spirocycle form of BMSRH opened via coordination with Cu2+ in a 1:1 stoichiometry and their association constant is determined as 3.2×10(4) L mol(-1). Experimental results indicate that the BMSRH can provide a rapid, selective and sensitive response to Cu2+ with a linear dynamic range 0.667-240 μmol/L. Common interferent ions do not show any interference on the Cu2+ determination. It is anticipated that BMSRH can be a good candidate probe and has potential application for Cu2+ determination. The proposed probe exhibits the following advantages: a quick, simple and facile synthesis.

A selectively fluorescein-based colorimetric probe for detecting copper(II) ion

A novel fluorescein derivative furfuraldehyde fluorescein hydrazone (FFH) has been synthesized by reacting fluorescein hydrazide with furfuraldehyde and characterized by (1)H NMR, (13)C NMR, MS and elemental analysis. Addition of Cu(2+) to the solution of FFH results in a rapid color change from colorless to yellow together with an obvious new band appeared at 502 nm in the UV-vis absorption spectra. This change is attributed to the spirocycle form of FFH opened via coordination with Cu(2+) in a 1:1 stoichiometry and their association constant is determined as 6.1×10(4) L mol(-1). Experimental results indicate that the FFH can provide a rapid, selective and sensitive response to Cu(2+) with a linear dynamic range 6.6-330 μmol/L. Common interferent ions do not show any interference on the Cu(2+) determination. It is anticipated that FFH can be a good candidate probe and has potential application for Cu(2+) determination in aqueous solution.