Piperazine-based new sensor: selective ratiometric sensing of Fe3+, logic gate construction and cell imaging

Newly designed and synthesised chemosensor 1 selectively recognises Fe³⁺ ions in CHCl₃–MeOH (1:1, v/v) by showing ratiometric change in emission and green colouration of the solution under the exposure of UV light. The ensemble 1·Fe³⁺ selectively detects F^?  ions over other halides and the phenomenon is useful to construct combinatorial logic gate. Furthermore, the probe 1 can be used for in vitro detection of Fe³⁺ in human cervical cancer (HeLa) cells.     

Single-Molecule White-Light-Emitting Starburst Donor-Acceptor Triphenylamine Derivatives and Their Application as Ratiometric Luminescent Molecular Thermometers

White-light emission (WLE) from a single molecule is a highly desirable alternative to a complex mixture of complementary colour emitters, which suffers from poor stability and reproducibility for potential use in organic electronic devices and lighting applications. We report single-molecule WLE both in solution and thin films by judiciously controlled π-electron delocalisation between the triarylamine subchromophoric units. Triphenylamine (TPA) forms the central core, and the phenyl rings are substituted with the electron-deficient acceptor 3-ethylrhodanine (Rh) and electron-rich donors triphenylamine or carbazole. The enforced biphenyl configuration of the TPA core and the other donors renders the π-conjugation across the entire chromophore poor, thus the individual subchromophoric units retain their individual emission characteristics, which cover all three primary colour emissions, that is, red, green and blue (RGB). TPA−Rh units exhibit broad fluorescence in the green-red region originating from the local excited (LE) state and intramolecular charge transfer state (ICT), strongly influenced by the solvent, water, and temperature. Different fluorescence parameters, including spectral maxima, ratiometric changes in ICT emission at the expense of blue emission from terminal donor units, and changes in lifetime, have a linear relationship with temperature between 180–330 K, thus the molecules can function as a multiparameter luminescent molecular thermometer. A temperature coefficient of 0.19 K⁻¹ in ratiometric fluorescence changes along with a spectral shift of 0.3 nm K⁻¹ and their workability over the wide temperature makes these molecules promising materials for potential applications. At lower temperatures, individual subchromophoric properties subside because of the reduced dihedral angle of biphenyl, and fluorescence from the whole molecule becomes dominant.     

A new intramolecular charge transfer receptor as a selective ratiometric ‘off-on’ sensor for Zn

A new intramolecular charge transfer (ICT) probe 3 is found to display a highly selective photophysical response in the presence of Zn²⁺, among various biologically significant metal ions examined. The absorption band of 3 is red shifted by 84 nm and the fluorescence intensity increases 13-fold in the presence of Zn²⁺. The binding interaction follows the order Zn²⁺ > Cd²⁺ > Mg²⁺ > Ba²⁺ > Ca²⁺ > K⁺ ≅ Na⁺ ≅ Li⁺ and the stability constant for 3 + Zn²⁺ is over an order of magnitude higher compared to biologically competing Ca²⁺ and Mg²⁺.     

Colorimetric and Fluorescent Bimodal Ratiometric Probes for pH Sensing of Living Cells

pH measurement is widely used in many fields. Ratiometric pH sensing is an important way to improve the detection accuracy. Herein, five water‐soluble cationic porphyrin derivatives were synthesized and their optical property changes with pH value were investigated. Their pH‐dependent assembly/disassembly behaviors caused significant changes in both absorption and fluorescence spectra, thus making them promising bimodal ratiometric probes for both colorimetric and fluorescent pH sensing. Different substituent identity and position confer these probes with different sensitive pH‐sensing ranges, and the substituent position gives a larger effect. By selecting different porphyrins, different signal intensity ratios and different fluorescence excitation wavelengths, sensitive pH sensing can be achieved in the range of 2.1–8.0. Having demonstrated the excellent reversibility, good accuracy and low cytotoxicity of the probes, they were successfully applied in pH sensing inside living cells.     

Ratiometric Fluorescence Imaging of Cellular Polarity: Decrease in Mitochondrial Polarity in Cancer Cells

Mitochondrial polarity strongly influences the intracellular transportation of proteins and interactions between biomacromolecules. The first fluorescent probe capable of the ratiometric imaging of mitochondrial polarity is reported. The probe, termed BOB, has two absorption maxima (λ_abs=426 and 561 nm) and two emission maxima—a strong green emission (λ_em=467 nm) and a weak red emission (642 nm in methanol)—when excited at 405 nm. However, only the green emission is markedly sensitive to polarity changes, thus providing a ratiometric fluorescence response with a good linear relationship in both extensive and narrow ranges of solution polarity. BOB possesses high specificity to mitochondria (R_r=0.96) that is independent of the mitochondrial membrane potential. The mitochondrial polarity in cancer cells was found to be lower than that of normal cells by ratiometric fluorescence imaging with BOB. The difference in mitochondrial polarity might be used to distinguish cancer cells from normal cells.     

聚电解质诱导的硫代黄素 T 激基缔合物及其对温度的荧光比率传感

研究了在水溶液中阴离子聚电解质聚苯乙烯磺酸钠(PSS)对阳离子型染料硫代黄素T(ThT)荧光光谱的影响,并考察了PSS存在下,ThT在水溶液中所形成激基缔合物的影响因素。实验证明,通过静电吸引作用,PSS可以增加ThT的局部浓度,从而显著地促进ThT激基缔合物的形成;ThT单体及其激基缔合物荧光强度(IM及IE)随温度的变化发生有规律的变化,ln(IE/IM)与1/T有较好的线性关系,据此可建立一种新型的对温度敏感的可裸眼识别的荧光比率传感,该传感可有效地消除激发光强度的不稳定性和光强漂移等环境因素的影响,提高了识别的准确度。     

A tunable ratiometric pH sensor based on carbon nanodots for the quantitative measurement of the intracellular pH of whole cells

The whole picture: Carbon nanodots labeled with two fluorescent dyes have been developed as a tunable ratiometric pH sensor to measure intracellular pH. The nanosensor shows good biocompatibility and cellular dispersibility. Quantitative determinations on intact HeLa cells and pH fluctuations associated with oxidative stress were performed.     

Construction of Fluorescent Probes Via Protection/Deprotection of Functional Groups: A Ratiometric Fluorescent Probe for Cu2+

Herein a ratiometric fluorescent Cu²⁺ probe was rationally constructed in a straightforward manner with the concept of aldehyde group protection/deprotection. The probe showed a ratiometric fluorescent response to Cu²⁺ with a large emission wavelength shift (>100 nm) and displayed high selectivity for Cu²⁺ over other metal ions due to distinct deprotection conditions. In addition, a Cu²⁺‐promoted dethioacetalization mechanism was proposed.     

Monitoring Local pH of Membranous Aggregates via Ratiometric Color Changing Response

A series of oxidized di(indolyl)arylmethanes (DIAM) with polyaromatic signaling moieties have been designed for monitoring local pH at the interfacial region of surfactant aggregates, such as micelles and vesicles. The oxidized DIAMs show changes in solution color from red to yellow when incorporated in cationic surfactants (at pH 7.4) and yellow to reddish pink when exposed to negatively-charged surfactants (at pH 5.0). The changes in surface charge can influence the interfacial pH (distinct from bulk pH of the medium) of the surfactant aggregates. The mechanistic studies indicate that the red-shifted absorption maxima observed in the presence of anionic amphiphiles (acidic local pH) originated from the protonated species. On the contrary, maxima in the blue region, triggered by positively charged amphiphiles (basic local pH), is attributed to the zwitterionic species. Such prototropic equilibrium affects charge transfer states of the molecules along with their self-assembly properties. Thus, it is evident that probes can predict as well as quantify the local pH change using the pseudophase ion exchange formalism. Also, the probes can detect the presence of anionic amphiphiles even when bound to phospholipid membranes.