Fluorescent Films Based on Molecular-Gel Networks and Their Sensing Performances

A pyrene-capped terthiophene of cholesteryl derivative (CholG-3T-Py) was designed, synthesized, and utilized for the fabrication of a fluorescent film. Unlike the commonly adopted direct-coating method, the film was fabricated by the physical immobilization of the fluorophore, CholG-3T-Py, onto a glass plate surface via preformed low-molecular-mass gelator (LMMGs)-based molecular-gel networks. The photophysical behavior of the film as prepared and its sensing performances to nitrobenzene (NB) were conducted after activation with toluene. It was found that the film as prepared and activated is sensitive to the presence of NB, and the sensing process is fully reversible. Furthermore, the effects of commonly found interferents, including structural analogues, raw materials, which are commonly used for the production of NB, and other nitroaromatics (NACs), on the sensing process were also tested. It was shown that only aniline and phenol possess slight interference. The present work not only extends the applications of LMMGs-based molecular gels but also provids a new approach for preparation of micro- and nano-structure-based fluorescent sensing films

Novel BODIPY-Based Fluorescence Turn-on Sensor for Fe³⁺ and Its Bioimaging Application in Living Cells

A novel boron-dipyrromethene (BODIPY) based fluorescence turn-on sensor for detecting Fe³⁺ in aqueous media is reported with 23-fold fluorescence enhancement. The sensor is comprised of a combination of BODIPY fluorophore and a new Fe³⁺-recognizing cryptand that exhibits high selectivity, sensitivity, and reversibility toward Fe³⁺ detection. Cell imaging studies demonstrate that this sensor is capable of sensing Fe³⁺ in living cells

Fluorenyl-Loaded Quatsome Nanostructured Fluorescent Probes

Delivery of hydrophobic materials in biological systems, for example, contrast agents or drugs, is an obdurate challenge, severely restricting the use of materials with otherwise advantageous properties. The synthesis and characterization of a highly stable and water-soluble nanovesicle, referred to as a quatsome (QS, vesicle prepared from cholesterol and amphiphilic quaternary amines), that allowed the nanostructuration of a nonwater soluble fluorene-based probe are reported. Photophysical properties of fluorenyl–quatsome nanovesicles were investigated via ultraviolet–visible absorption and fluorescence spectroscopy in various solvents. Colloidal stability and morphology of the nanostructured fluorescent probes were studied via cryogenic transmission electronic microscopy, revealing a “patchy” quatsome vascular morphology. As an example of the utility of these fluorescent nanoprobes, examination of cellular distribution was evaluated in HCT 116 (an epithelial colorectal carcinoma cell line) and COS-7 (an African green monkey kidney cell line) cell lines, demonstrating the selective localization of <b>C-QS</b> and <b>M-QS</b> vesicles in lysosomes with high Pearson’s colocalization coefficient, where <b>C-QS</b> and <b>M-QS</b> refer to quatsomes prepared with hexadecyltrimethylammonium bromide or tetradecyldimethylbenzylammonium chloride, respectively. Further experiments demonstrated their use in time-dependent lysosomal tracking

Fabrication of a Novel Cholic Acid Modified OPE-Based Fluorescent Film and Its Sensing Performances to Inorganic Acids in Acetone

A self-assembled monolayer (SAM)-based fluorescent film was designed and prepared by chemical immobilization of a novel oligo­(<i>p</i>-phenylene- ethynylene) (OPE) with cholic acid moieties at the ends of its side chains (Film 1). As a control, a similar film, Film 2, of which OPE brings no side chains, was also prepared. The structures of the films were characterized by contact angle, XPS, ATR-IR and fluorescence measurements. Fluorescence studies revealed that the emission of Film 1 is sensitive to the presence of trace amount of some inorganic acids in acetone, such as HCl, H₂SO₄, HNO₃, and H₃PO₄, etc., whereas the acids as studied showed little effect on the emission of Film 2. The difference in the sensing performances of the two films have been rationalized by considering presence or absence of a possible cavity, a substructure appearing above the OPE adlayer which is something like a dimer of cholic acid (CholA) formed at specific environment

Fabrication of a Novel Cholic Acid Modified OPE-Based Fluorescent Film and Its Sensing Performances to Inorganic Acids in Acetone

A self-assembled monolayer (SAM)-based fluorescent film was designed and prepared by chemical immobilization of a novel oligo­(<i>p</i>-phenylene- ethynylene) (OPE) with cholic acid moieties at the ends of its side chains (Film 1). As a control, a similar film, Film 2, of which OPE brings no side chains, was also prepared. The structures of the films were characterized by contact angle, XPS, ATR-IR and fluorescence measurements. Fluorescence studies revealed that the emission of Film 1 is sensitive to the presence of trace amount of some inorganic acids in acetone, such as HCl, H₂SO₄, HNO₃, and H₃PO₄, etc., whereas the acids as studied showed little effect on the emission of Film 2. The difference in the sensing performances of the two films have been rationalized by considering presence or absence of a possible cavity, a substructure appearing above the OPE adlayer which is something like a dimer of cholic acid (CholA) formed at specific environment

A Butterfly-Shaped Pyrene Derivative of Cholesterol and Its Uses as a Fluorescent Probe

A butterfly-shaped pyrene derivative of cholesterol, namely, <i>N</i>,<i>N</i>′-(ethane-1,2-diyl)-bis­(<i>N</i>-(2-(chol-amino)­ethyl)­pyrene-1-sulfonamide) (ECPS), has been designed and synthesized. Solvent effect studies revealed that in good solvents such as <i>n</i>-hexane, benzene, and 1,4-dioxane, the profile of the fluorescence emission of the compound is characterized by pyrene monomer emission, but in poor solvent such as water, the emission is dominated by pyrene excimer emission. Quantitatively speaking, the ratio of the excimer emission to monomer emission changes from 50 to 0 when ECPS is dissolved in water and <i>n</i>-hexane, respectively. In contrast, for a commonly used polarity probe pyrene, the ratio of I₃/I₁ varies only from ∼0.6 to ∼1.7, where I₃ and I₁ stand for the intensities of the fluorescence emission at peak 3 and peak 1, respectively. This value suggests that a more powerful discriminating ability of the new compound in polarity sensing. Furthermore, unlike the main components of the compound, pyrene and cholesterol, its main chain is composed of multiple hydrophilic structures, and it is this structure that makes the emission of the compound in organic solvents sensitive to the presence of water. Accordingly, the applicability of the compound in determination of the trace amount of water in some organic solvents was evaluated. As expected, the detection limit of the compound toward water in acetonitrile reaches 7 ppm, a result never reached before. Furthermore, the fluorescence emission of the compound is also sensitive to viscosity variation. Therefore, it is assumed that ECPS may be used both as a polarity probe and a viscosity probe. On the bases of a series of steady-state and time-resolved fluorescence, as well as dynamic light scattering studies, a structural model was proposed to rationalize the fluorescence behavior of the compound in different solvents and its polarity and viscosity probing performances

Linear Photophysics and Femtosecond Nonlinear Spectroscopy of a Star-Shaped Squaraine Derivative with Efficient Two-Photon Absorption

The synthesis, comprehensive linear photophysical and photochemical study, two-photon absorption (2PA) spectrum, ultrafast relaxation kinetics in the excited states, and efficient superluminescence properties of a new symmetrical three-armed star-shaped squaraine derivative (<b>1</b>) are presented. The steady-state spectral parameters of <b>1</b> in a number of organic solvents, including fluorescence excitation anisotropy spectra, revealed a weak interaction between the squaraine branches and the effect of symmetry breaking in the ground electronic state. The degenerate 2PA spectrum of <b>1</b> was obtained over a broad spectral range with a maximum cross section of ∼8000 GM using the open aperture Z-scan technique. The nature of the fast dynamic processes in the excited electronic states of <b>1</b> was investigated by the femtosecond transient absorption pump–probe method, revealing characteristic relaxation times of ∼3–4 ps. The efficient superluminescence emission of <b>1</b> was observed in relatively low concentration solution (≈ 2.3·10^–4 M) under femtosecond transverse pumping. A quantum-chemical study of <b>1</b> was performed using ZINDO/S//DFTB theory levels. Simulated 1PA and 2PA absorption spectra were found to be in a good agreement with experimental data. The figure of merit for <b>1</b> is ∼10¹¹ GM, one of the highest values ever reported for two-photon fluorescence molecular probes, suggesting strong potential for its application in two-photon fluorescence microscopy and bioimaging

Systematic Molecular Engineering of a Series of Aniline-Based Squaraine Dyes and Their Structure-Related Properties

With the objective of developing new near-infrared fluorescent probes and understanding the effect molecular structure exerts on physical properties, a series of aniline-based squaraine dyes with different number and position of methoxy substituents adjacent to the squaraine core were synthesized and investigated. Using both computational and experimental methods, we found that the subtle changes of the number or position of the methoxy substituents influenced the twisting angle of the structure and led to significant variations in optical properties. Moreover, the methoxy substituent also affected aggregation behavior due to steric effects. The X-ray crystal structure of one of the key members of the series, <b>SD-2a</b>, clearly demonstrates the distortion between the four-membered squaraine core and the adjacent aniline ring due to methoxy substitution. Structure-related fast relaxation processes were investigated by femtosecond pump–probe experiments and transient absorption spectra. Quantum chemical calculations and essential state models were exploited to analyze the primary experimental results. The comprehensive investigation of structure-related properties of dihydroxylaniline-based squaraine dyes, with systematic substitution of OH by OCH₃ functional groups, serves as a guide for the design of novel squaraine dyes for photonics applications