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Fluoran dyes, a large family of colourants, have been widely used as thermosensitive dyes in print industry by taking advantage of the thermo-controlled interconversions between the colorless spirolactone and the colored zwitterion forms. But few attentions have been paid to their fluorescence properties. In this paper, the fluorescence regulation of 4-aminobenzofluoran dye 1 by introducing of electron-deficient acetyl group to tune the energy level of the highest occupied molecular orbital (HOMO) of the amino group has been carried out. Based on this strategy, the N -acetylated product BF derived from its precursor 1 shows stable UV–Vis and fluorescence spectra in water from pH 1.0 to 12.0 due to the blocking of the photoinduced electron transfer (PET) process from the amino group to the excited state of fluoran chromophore. Moreover, BF is cell permeable and can be used as signal reporter for the design of fluorescence probes by taking advantage of the fluorescence controlled mechanism of the ring opening and closing chemical processes of the spirolactone platform. By using BF as precursor, a highly sensitive and selective fluorescent probe BF-Cu for Cu 2+ was synthesized by introducing a Cu 2+ -responsive water soluble 2-hydroxylethyl hydrazine functional group. We expect that the fluorescence recovery of fluoran dyes via the regulation of the HOMO energy level of the amino group enable an additional synthetic effort on the development of fluorescence fluoran dyes and expansion of their applications. [ABSTRACT FROM AUTHOR]

A novel fluoran-based fluorescent probe 2 has been designed and synthesized by using a strategy of blocking the intramolecular photoinduced electron transfer (PET) process. The probe keeps a ring-closed spirolactone structure in aqueous buffer solution. However, the oxidation of the probe by ClO − perturbs a new equilibrium of the structural interconversion between the nonfluorescent spirolactone and the fluorescent ring-opened zwitterion, which generates a highly selective fluorescent probe for ClO − . Meanwhile, the probe is cell membrane permeable and can be utilized as fluorescent probe for imaging ClO − in living cells. [ABSTRACT FROM AUTHOR]

A novel pyridyl functionalized rhodamine dye with large Stokes shift and stable fluorescence in water was facilely prepared and utilized for a Hg2+-selective probe. [Display omitted] • A Rhodamine derivative PR has been prepared with Stokes shift of 81 nm. • Probe PRHg is synthesized, presenting high selectivity and sensitivity (LOD: 8.5 nM) to Hg2+. • PRHg exhibits great potential for tracing Hg2+ in living cells. Rhodamines gain sustained attention owing to their great potential for probe design applications. Herein, the facile preparation of a new pyridyl functionalized rhodamine dye PR is reported, which has stable fluorescence signal in water with maximum emission peak at 594 nm and Stokes shift of 81 nm. Based on dye PR , a new fluorescent probe PRHg has been developed by modifying the spirolactone of PR with hydrazine hydrate so as to produce spirolactam recognizing group for sensing of Hg2+. PRHg exhibits high selectivity and sensitivity towards Hg2+ in water/ethanol (v/v = 4/1, pH = 7.0) by a specific Hg2+-binding promoted spirolactam ring opening and hydrolyzing process. And, the detection limit for Hg2+ is evaluated to be 8.5 nM. Besides, the probe can respond to Hg2+ within 40 min and over a wide pH range from 4.0 to 10.0. Moreover, PRHg (40 µM) performs low cytotoxicity to HeLa cells (over 91.0 % cell survival rate), which allows the probe to be employed for tracing intracellular Hg2+ by fluorescence imaging. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel quinoline-rhodamine hybrid probe P7RHg has been facilely prepared. • P7RHg can be used for raitiomet-ricly sensing of Hg2+ in water with well separated emission peaks. • P7RHg exhibits selectivity to Hg2+ with nearly 90-fold fluorescent ratio enhancement. • P7RHg shows promising potential in tracing intracellular Hg2+. To develop efficient tools for monitoring toxicant Hg2+ in aqueous solution attracts great attention because the abnormal distribution of Hg2+ in environment poses great threat to human health. We here report the preparation of a novel quinoline-rhodamine hybrid fluorescent probe P7RHg for ratiometricly sensing of Hg2+ in water, with a spirolactam-thiosemicarbazide reaction group. Upon treatment by Hg2+, the ratio of fluorescence intensity (F 600 /F 460) exhibits nearly 90-fold enhancement, presenting two well-resolved emission peaks (140 nm). Meanwhile, the specific Hg2+-induced desulfurization provides probe P7RHg an excellent selectivity to Hg2+, with a detection limit of 8.6 nM. Moreover, the low cytotoxicity allows P7RHg to be employed for tracing Hg2+ in living cells by confocal fluorescence imaging. [ABSTRACT FROM AUTHOR]

Based on a fluoran skeleton, we herein reported a new fluorescent probe FLACu for Cu2+ by facile modification of the spirolactone of dye 1 with phenylhydrazine. Taking advantage of the spirolactam moiety, FLACu only delivers a specific "off-on" fluorescence signal output towards Cu2+ when treated with various metal ions, which has been well elucidated as the result of spirolactam ring opening and hydrolysis processes induced by copper ion. Meanwhile, the limit of detection (LOD) for FLACu has been estimated to be 35.4 nM and a pH range of 5.0–9.0 is evaluated to be suitable for Cu2+ detection. Significantly, FLACu shows low cell cytotoxicity and can be further ultilzied in the detection of exogenous Cu2+ in the living Hela cells. [ABSTRACT FROM AUTHOR]

A novel indazole fused rhodamine fluorescent dye with large Stokes shift and stable fluorescence in water for constructing an Hg2+-selective probe and cell imaging applications. [Display omitted] • A indazole fused rhodamine dye InRh has been prepared with stable fluroescence in water. • Probe InRhH can respond to Hg2+ with high selectivity and sensitivity by fluorescence and absorption spectra. • Probe InRhH shows promising application in tracing Hg2+ in living cells. Developing selective and sensitive probes for mercury ion (Hg2+) is of great significance because Hg2+ exhibits high toxicity and poses a potential threat to public health and the environment. Herein, a newly designed indazole fused rhodamine dye InRh has been prepared, which shows stable fluorescent signals in water at a wide pH range of 1.0–10.0. Based on the dye InRh, a novel fluorescent probe InRhH for Hg2+ is further developed by modifying the spirolactone ring of InRh to form a closed spirolactam ring. The probe shows selective fluorescence "off–on" signal changes to Hg2+ with a visible color change and response time of 40 min in H 2 O/CH 3 CN (pH = 6.0, v/v = 4/1), and the detection limit for Hg2+ is measured to be 0.33 nM. The recognition mechanism for Hg2+ can be ascribed to the binding interactions between Hg2+ and probe in a 2: 1 coordination mode, which promotes the occurrence of spirolactam ring opening and further hydrolysis. In addition, the InRhH can be applied for test strip experiments and tracing 10−6 M level Hg2+ with visible color change. Furthermore, the suitable cytotoxicity allows the probe to apply for sensing Hg2+ in living HeLa cells by fluorescence imaging. [ABSTRACT FROM AUTHOR]

The development of mercury ion selective fluorescent probe is significant because it is one of toxic heavy metals and poses great risks and hazards to human health. Herein, we develop a mercury ion-selective fluorescent probe, namely IB, based on imidazole decorated benzothiadiazole that obtained by a facile palladium catalytic C-N coupling reaction. IB exhibits high selectivity and sensitivity towards mercury ion in water with nearly 32-fold fluorescent enhancement. The detection limit is calculated to be 0.93 nmol/L. In addition, the sensing of mercury ion can be conducted in a wide pH scope ranging from 4.0 to 10.0. Subsequently, the mercury ion elicits fluorescence of IB solution can be quenched by the addition of cyanide anions, showing "off-on-off" fluorescence transformation with at least 5 cycles, demonstrating the reversible sensing ability of IB. Furthermore, an INHIBIT logical detector has been developed using mercury ion and cyanide anions as inputs and fluorescence of IB as output. Significantly, IB can be utilized for mercury ion detection in real water sample. [ABSTRACT FROM AUTHOR]

• Two thiazole-fused fluoran-based fluorescent probes for copper ions have been prepared. • The two probes show high selectivity and sensitivity for copper ions. • MTFH achieves red emission (632 nm) towards copper ions due to the methyl functionalization. • The two probes can be utilized for tracing intracellular copper ions. In this work, two thiazole-fused fluoran-based fluorescent probes 8′-(diethylamino)-2-((2-hydroxyethyl) amino)spiro[isoindoline-1,11′-xantheno[2, 1- d ]thiazol]-3-one (TFH) and (8′-(diethylamino)-2-((2-hydroxyethyl)amino)-3′-methyl-3-oxospiro[isoindoline-1,11′-xantheno[2,1- d ]thiazol]-3′-ium).BF 4 (MTFH) have been prepared for copper ions. It should be noted that MTFH achieves red emission (632 nm) compared with TFH in the presence of copper ion, which mainly can be attributed to the methylation of molecule MTFH that induced more stronger ICT effect. The two probes show selective fluorescence off-on signal changes towards copper ions with detection limits of 8.8 and 60.8 nM. Copper ion detection can be conducted in a wide pH range including the physiological pH environment. Both TFH and MTFH exhibit suitable cytotoxicity and have been used for copper ion tracing in living cells. However, no other significant improvements of MTFH in sensing performance can be observed when compared with TFH. Two thiazole-fused fluoran-based fluorescent probes have been prepared for selectively and sensitively sensing copper ions, in particular, the methyl functionalization probe achieves red emission mainly due to a stronger ICT effect. [Display omitted] [ABSTRACT FROM AUTHOR]

A terpyridyl-rhodamine based probe has been designed and prepared for the sensitive and discriminative detection of Hg2+ and Cu2+ in water by dual/single emission change and applications in constructing a combinatorial logic gate and cell imaging. [Display omitted] • A new terpyridyl-rhodamine hybrid dye TR and sensor TRH have been facilely prepared. • TRH can discriminatively sense Hg2+ and Cu2+ in water with high sensitivity. • TRH can be employed for the construction of a combinatorial logic gate. • TRH can be applied for the discriminative sensing of Hg2+ and Cu2+ in living cells. Sensitive and discriminative sensing of more than one analyte with a single fluorescent probe is significant and challenging. Herein a new terpyridyl-rhodamine hybrid, namely TRH, has been rationally designed and prepared with two responsive groups in the molecular structure, which facilitate the discriminative detection of Hg2+ and Cu2+ ions in water with detection limits of 4.9 and 53.3 nM by ratiometric fluorescence change (F 595 /F 485) and fluorescence quenching, respectively. Investigations show that the selectivity to Hg2+ ions can be attributed to Hg2+-promoted spirolactam ring opening and further hydrolysis, followed by a through-bond energy transfer (TBET) process. The selective fluorescence quenching to Cu2+ ions probably can be ascribed to the binding Cu2+ to terpyridyl that triggers a ligand-to-metal charge transfer (LMCT) process, which can also efficiently inhibit the TBET process induced by Hg2+ ions and promotes the discriminative sensing of Cu (II) and Hg (II). In addition, the fluorescent responses to Hg2+ and Cu2+ ions cover a wide pH range. Moreover, a combinatorial logic gate with the functions of NOR and INHIBIT has been fabricated by using Hg2+ and Cu2+ ions as chemical input signals, and fluorescence at 485 and 595 nm as output signals. Besides, TRH also exhibits sensitive and discriminative sensing ability to Hg2+ and Cu2+ ions by the fluorescence of rhodamine fluorophore. Significantly, based on the fluorescence signal output of rhodamine moiety, TRH can be used as a tracer for the discriminative sensing of Hg2+ and Cu2+ ions by using living cells. [ABSTRACT FROM AUTHOR]

Biological thiols, such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) are important for maintaining the cellular redox equilibrium and play critical roles in physiological and pathological processes. It is necessary to detect Cys, Hcy and GSH for obtaining important physiological and pathological information, which would promote the development of the medical profession. In this paper, we have successfully developed a new fluorescent probe OH1-NBD for Hcy detection. Based on the nucleophilic aromatic substitution (S N Ar) and rearrangement cascade reaction and the distance-dependent PET process, OH1-NBD shows to be a selective turn-on fluorescent probe for Hcy with a fast (a few minutes) and sensitive (16 nM) response. It can function as a fluorescence probe for imaging of Hcy in the living cell. At the same time, it can also be used for living cells as a potential probe for biothiol-relevant oxidant-governed redox status assay. We expect that the probe will provide a valuable approach to gain a better understanding of the roles of biothiols especially Hcy. [ABSTRACT FROM AUTHOR]

A fluoran-phenothiazine hybrid fluorescent probe for selective sensing of Fe3+ and ClO− has been rationally designed and prepared with application in fluorescence imaging. [Display omitted] • A fluoran-phenothiazine hybrid fluorescent probe FP has been designed and prepared. • FP shows high selectivity and sensitivity towards Fe3+ and ClO− by dual emission. • The low cytotoxicity allows FP to trace intracellular Fe3+ by cell imaging. Bifunctional fluorescent probes with dual-emission response attract extensive attention. A novel fluorescent probe FP , a hybrid of fluoran and phenothiazine, has been designed and synthesized for selective sensing of Fe3+ and ClO− with dual-emission changes, which involes mechanisms of Fe3+-promoted spirolactone ring opening and ClO−-induced oxidation of phenothiazine moiety, respectively. In addition, the detection limits for Fe3+ and ClO− were estimated to be 49.1 and 35.9 nM, respectively. Significantly, FP can be employed as an tracer for the detection of Fe3+ ions within living HeLa cells by fluorescence imaging. [ABSTRACT FROM AUTHOR]

A new fluorescent probe Lyso-Fl has been facilely prepared by an esterification reaction of spironolactone fluoran dye Rdi with ethanol, which shows viscosity-selective response by fluorescence. The new probe delivers obvious fluorescence signal enhancement when environmental viscosity changes from 1.01 cP (water) to 1256 cP (98% glycerol). And, both the emission intensity (575 nm) and fluorescence lifetime of Lyso-Fl exhibit individually good linear relationships with the solution viscosity. Besides, Lyso-Fl gives a selective response to viscosity among various biological species and exhibits pH-independent (1–10) fluorescent signals towards viscosity. More importantly, Lyso-Fl shows low cytotoxicity and can be utilized for monitoring of dexamethasone-stimulated viscosity enhancement by cell imaging with excellent lysosome-targeted performance, promoting it a promising fluorescent probe for lysosomal viscosity detection. A fluoran-based fluorescent probe Lyso-Fl for viscosity has been conveniently prepared with excellent performance in monitoring of lysosomal viscosity changes via fluorescence imaging. Unlabelled Image • A fluoran-based fluorescent probe Lyso-Fl has been facilely prepared. • Lyso-Fl delivers obvious fluorescence enhancement with viscosity increase. • Lyso-Fl shows low cytotoxicity. • Lyso-Fl can be utilized for monitoring of viscosity enhancement by cell imaging with excellent lysosome-targeted performance. [ABSTRACT FROM AUTHOR]