Salicylaldehyde Azine Research Articles

Significant emission enhancement of a bola-amphiphile with salicylaldehyde azine moiety induced by the formation of [2]pseudorotaxane with γ-cyclodextrin

The emission of a bola-amphiphile with salicyladazine moiety was significantly enhanced by the formation of [2]pseudorotaxane with γ-cyclodextrin, which can specifically localize in mitochondria of living cells.

Trace analysis of uranyl ion (UO22+) in aqueous solution by fluorescence turn-on detection via aggregation induced emission enhancement effect

A sensitive fluorescence turn-on method for trace amounts of uranyl ion (UO22+) in solution has been developed in this study, based on aggregation induced emission enhancement (AIEE) characteristics of 4-pethoxycarboxyl salicylaldehyde azine (PCSA) induced by complex interaction between UO22+ and PCSA. Under optimized conditions, a fluorescence enhancement at 540nm could be observed, which was linearly related to the concentration of UO22+ in the range of 1–25ppb (part per billion). Analytical data showed that a detection limit of 0.2ppb was achieved with the relative standard deviation (R.S.D.) 1.3% (n=5). The proposed method was successfully utilized in quantifying UO22+ in fuel processing wastewaters.

A fluorescent probe for thiols based on aggregation-induced emission and its application in live-cell imaging

A turn-on fluorescent probe DNBS-CSA is reported here with selective detection of thiols over other amino acids. Probe DNBS-CSA possesses the widely-used thiol-selective 2,4-dinitrobenzenesulfonyl (DNBS) group to react with thiols and release the fluorescent salicylaldehyde azine with aggregation-induced emission (AIE) characteristics. The use of AIE dye prevented the sensor from aggregation-induced fluorescence quenching which is challenging for other thiols sensors. Upon the addition of cysteine (Cys) to DNBS-CSA in aqueous solution (10 mM PBS buffer at pH 7.4 containing 30% DMSO), an intense fluorescence enhancement was observed at 558 nm with a large stokes shift of ∼170 nm. Under the optimal condition, the fluorescence intensity linearly increased with the concentration of Cys in the range of 8–18 μM with a correlation coefficient of R2 = 0.991. The fluorescence enhancement of DNBS-CSA upon addition of Cys on test paper was also observed, enabling DNBS-CSA function as solid materials (such as test papers) for thiols detection. The detection of thiols in serum samples was successfully performed. With good cell permeability, the probe was applied to the imaging of thiols in HEK 293T cells.

Fluorescent staining of protein in SDS polyacrylamide gels by salicylaldehyde azine

As a noncovalent fluorescence probe, in this study, salicylaldehyde azine (SA) was introduced as a sensitive fluorescence-based dye for detecting proteins both in 1D and 2D polyacrylamide electrophoresis gels. Down to 0.2 ng of single protein band could be detected within 1 h, which is similar to that of glutaraldehyde-silver stain, but approximately four times higher than that of SYPRO Ruby fluorescent stain. Furthermore, comparative analysis of the MS compatibility of SA stain with SYPRO Ruby stain indicated that SA stain is compatible with the downstream of protein identification by LC-MS/MS. Additionally, the probable mechanism of the SA stain was investigated by molecular docking. The results demonstrated that the interaction between SA and protein was mainly contributed by hydrogen bonding and hydrophobic forces.

Halogenated salicylaldehyde azines: The heavy atom effect on aggregation-induced emission enhancement properties

This study investigates the heavy-atom effect (HAE) on aggregation-induced emission enhancement (AIEE) properties of salicylaldehyde azines. For this purpose, a series of halogenated salicylaldehyde azine derivatives, namely, chloro-salicylaldehyde azine (1), bromo-salicylaldehyde azine (2) and iodo-salicylaldehyde azine (3) are synthesized. 1 and 2 display typical AIEE characteristics of salicylaldehyde azine compounds; whereas for the iodo-substituent in 3, is found to be effective “external” heavy atom quenchers to salicylaldehyde azine fluorescence in aggregated state. Based on its weak fluorescence in aggregated state and relative strong fluorescence in dispersed state, 3 can also be applied as a turn-on fluorescence probe for egg albumin detection attributed to hydrophobic interaction.

Frequency upconversion and two-photon absorption of salicylaldehyde azine 1

Two-photon absorption and two-photon excitation fluorescence of salicylaldehyde azine 1 crystals were investigated. It was observed an intense visible fluorescence when this material was excited with a laser tuned at the near infrared region. Varying the laser intensity we characterized this phenomenon as a simultaneous two-photon laser absorption process. Using open aperture Z-scan measurements we characterized this two-photon absorption phenomenon and measured the value of the two-photon absorption cross-section of this molecule to be equal to 87GM. Our results indicate that this is a promising organic material aiming nonlinear photonics applications.

Salicylaldehyde azine cluster formation observed by cold‐spray ionization mass spectrometry

We installed a cold-spray ionization (CSI) source on a mass spectrometer to investigate the self-assembly behavior of an aggregation-induced emission enhancement system. Using a CSI source and the three-dimensional platform, a self-assembly system of a salicylaldehyde azine (SAA) was studied in mixture solution. This method permitted the determination of the structural information of the solution state, which cannot be detected by conventional mass spectrometry. In addition to the [M+H](+) ion (M is the SAA molecule), many major ion clusters such as [2M+Na](+) at m/z 503, [3M+Na](+) at m/z 743, [4M+Na](+) at m/z 983 and higher order aggregates were observed in the CSI mass spectra. However, many fragment ions, with the exception of cluster ions, appeared with high abundance when the ESI ion source was used due to the desolvation chamber temperature, suggesting that some aggregation can be detected at low temperatures. To investigate the effect of solvent on the aggregation, the CSI-mass spectrometry (MS) experiments of SAA in absolute ethanol solution and ethanol/water (good/poor solvent) mixture solution were conducted. The most abundant ion peak was protonated SAA (m/z 241) in absolute ethanol, but many cluster ions and some multiple charged ion peaks were observed after adding a small amount of water into the ethanol solution. The results showed good agreement with that inferred by the combinational analysis of scanning electron microscope and fluorescence microscopy, indicating that CSI-MS is capable of providing self-assembly information of labile molecules in the solution state.

The Reaction of Ethyl 2-oxo-2H-chromene-3-carboxylate with Hydrazine Hydrate

Although salicylaldehyde azine (3) was reported in 1985 as the single product of the reaction of ethyl 2-oxo-2H-chromene-3-carboxylate (1) with hydrazine hydrate, we identified another main reaction product, besides 3, which was identified as malono-hydrazide (4). In the last two decades, however, some articles have claimed that this reaction afforded exclusively hydrazide 2 and they have reported the use of this hydrazide 2 as a precursor in the syntheses of several heterocyclic compounds and hydrazones 6. We reported herein a study of the formation of 2 and a facile route for the synthesis of the target compounds N'-arylidene-2-oxo-2H-chromene-3-carbohydrazides 6a–f.

Proton Transfer Assisted Charge Transfer Phenomena in Photochromic Schiff Bases and Effect of –NEt2 Groups to the Anil Schiff Bases

Photochromic Schiff bases 5-diethylamino-2-[(4-diethylamino-benzylidene)-hydrazonomethyl]-phenol (DDBHP) and N,N'-bis(4-N,N-diethylaminosalisalidene) hydrazine (DEASH) with both the proton and charge transfer moieties have been synthesized, and their photophysical properties such as excited state intramolecular charge transfer (ICT) and proton transfer (ESIPT) processes have been reported on the basis of steady-state and time-resolved spectral measurement in various solvents. The ground-state six-membered intramolecular hydrogen bonding network at the proton transfer site accelerates the ESIPT process for these compounds. Both the compounds show large Stokes-shifted emission bands for proton transfer and charge transfer processes. The hydrogen bonding solvents play a crucial role in these photophysical processes. Excited-state dipole moment of DDBHP and DEASH calculated by the solvatochromic method supports the polar character of the charge transfer excited state. Introduction of -NEt(2) groups to the reported salicylaldehyde azine (SAA) Schiff base results an increase in fluorescence lifetime from femtosecond to picosecond time scale for the proton transfer process.

Long-living structures of photochromic salicylaldehyde azine: polarity and viscosity effects from nanoseconds to hours

In this study, we report on the effects of solvent viscosity and polarity on the photochromic salicylaldehyde azine (SAA) molecule by examining the steady-state and UV-visible absorption results in the time scale from nanoseconds to hours, in solution and in a polymer film. For the neutral structure, the viscosity strongly affects the lifetime of the photochromic (trans-keto) tautomer by suppressing the second order quenching process, and thus increasing the photochrome lifetimes in highly viscous solvents to 500 μs in polar triacetine, and to 65 μs in non-polar squalane. Trapping SAA in a non-polar polymer film (polyethylene) results in further elongation of the photochromic lifetime (700 μs) by one order of magnitude (with respect to that in squalane), due to the retardation of the intramolecular back-isomerization. Another species, living significantly longer and absorbing more in the UV comparing to the photochrome, was identified as the syn-enol tautomer. The lifetime of this tautomer, created in a competitive mechanism to the photochrome creation, is much longer in non-polar solvents (hundreds of minutes) than in polar ones (tens of minutes), opposite to the trend observed for the photochrome. For the SAA anion, the transient living on the ns-μs time scale can be exclusively assigned to the triplet state, which is not observed for the neutral form at room temperature.

Space group revsion of the triclinic polymorph of salicylaldehyde azine

The structure of the title compound, C14H12N2O2 {systematic name: 2,2′-[hydrazinediylidenebis(methanylyl­idene)]diphen­ol}, has already been determined in the triclinic space group P with Z = 4 [El-Medani, Aboaly, Abdalla & Ramadan (2004 ▶). Spectrosc. Lett. 37, 619–632]. However, the correct space group should be P21/c with Z = 4. This structure is a new polymorph of the already known monoclinic polymorph of salicyladehyde azine, which crystallizes in space group P21/n with Z = 2. The benzene rings form a dihedral angle of 46.12 (9)°. Two intramolucular O—H⋯N hydrogen bonds occur.

Synthesis, Antioxidant and Antibacterial Activities of Salicylaldehyde Azine

Salicylaldehyde azine (SA) were synthesized with salicylaldehyde and hydrazine hydrate as a raw material. The crystal structure was characterized by X-ray diffraction, as well as the total antioxidant capacity and antibacterial activities against Staphylococcus aureus and Escherichia coli were investigated. It was found that SA exhibited significant antibacterial activities and total antioxidant capacity.

Aldazine-based colorimetric sensors for Cu 2+ and Fe 3+

We have developed novel aldazine-based colorimetric chemosensors for Cu 2+ and Fe 3+. The aldazine ligands were synthesized by simple condensation of 4-diethylamino-salicylaldehyde and 8-hydroxyjulolidinal with hydrazine. The (4-diethylamino)-salicylaldehyde-azine ( SA) showed high selectivity and sensitivity towards Cu 2+ over the other alkali and transition metal ions. In the presence of Cu 2+, absorption band of SA at 425 nm red shifted to 545 nm. The color of solution changed from pale yellow to purple color. Interestingly, 8-hydroxyjulolidinal-azine ( JA) showed selectivity towards Fe 3+ over alkali and transition metal ions. In the presence of Fe 3+, the color of the ligand solution changed from pale yellow to violet. The absorption band of JA at 445 red shifted to 575 nm. The fluorescence of ligands SA and JA was completely quenched in the presence of Cu 2+ and Fe 3+, respectively. However, the quenched fluorescence of JA–Fe 3+ complex can be reversibly restored using cysteine.

Organic Crystalline Solids Response to Piezo/thermo Stimulus: Donor–Acceptor (D–A) Attached Salicylaldehyde Azine Derivatives

A salicylaldehyde azine-based derivative, which exhibited switchable solid-state fluorescence in response to external thermal and mechanical grinding stimulus, was reported in this study. Diffuse reflectance solid-state spectroscopy, fluorescence spectroscopy, solid-state 13C and 1H NMR spectroscopy, single crystal XRD analyses, powder X-ray diffractometry, and differential scanning calorimetry were used for investigating the changes of molecular packing modes. The multistimuli fluorescence originated from two distinctive crystalline lattices via different π–π interactions. The local dipole coupling among molecules with donor–planar–acceptor structure was evidenced to be the essential factor for the effective solid luminescence-switching properties.

4-(Diethylamino)salicylaldehyde azine

The title compound, C22H30N4O2, has a crystallographic inversion center located at the mid-point of the N—N single bond. Apart from the four ethyl C atoms, the non-H atoms are nearly coplanar with a mean deviation of 0.0596 (2) Å. An intra­molecular O—H⋯N hydrogen bond occurs. In the crystal, weak inter­molecular C—H⋯O hydrogen bonds link the mol­ecules into layers parallel to (100).

Confined Fast and Ultrafast Dynamics of a Photochromic Proton-Transfer Dye within a Zeolite Nanocage

We report on studies of salicylaldehyde azine (SAA) dissolved in dichloromethane solution and within the cages of the faujasite zeolite (NaX) using steady-state and femtosecond to nanosecond time-resolved spectroscopy. In solution, an excited-state intramolecular proton-transfer reaction takes place in less than 80 fs, leading to a keto-type tautomer. In contrast within NaX zeolite, a zwitterionic (Z) form is present both at S0 and S1 states, and a large hypsochromic shift of the stationary emission spectrum is observed. The increase in fluorescence lifetime upon encapsulation (from 54 ps to 0.2−2.8 ns) is mainly due to hindrance in twisting motion of the confined Z structure imposed by the nanocage. A significant dependence of the lifetimes on the guest concentration inside the zeolite indicates an interaction between neighboring guest molecules leading to a quenching of the fluorescence. The analysis of emission decays using stretched-exponential model suggests that the excited-state interactions between neighboring dyes play a key role in the deactivation of the trapped Z fluorophores. For the ultrafast relaxation dynamics of the SAA/NaX composite, intramolecular vibrational-energy redistribution and vibrational cooling process occur in longer times (up to 360 fs and 5 ps, respectively). Additionally, the presence of nonfluorescent twisted (n,π*) state is suggested to form in 6−10 ps. We believe that our results are important for a better understanding of the photocycle of azine-based photochromic material when interacting with nanomaterials.

What is the difference between the dynamics of anion- and keto-type of photochromic salicylaldehyde azine?

The normal and anion structures of salicylaldehyde azine (SAA) in solvents of different viscosities and polarities have been studied by means of femto- to nanosecond time-resolved emission techniques. In the normal form, an excited-state intramolecular proton-transfer (ESIPT) reaction takes place with a time constant shorter than 80 fs to produce an excited keto-type tautomer in which intramolecular-vibrational energy redistribution and vibrational cooling occur in 100 fs to 2 ps. The viscosity-dependent emission decay in the red part of the spectrum with 5-11 ps reflects a twisting motion leading to rotamers of these keto-type structures, most probably of (n,pi*) nature. For the anion type, the viscosity dependent rise-times (3 to 400 ps) at the red part of the emission, and the wavelength-dependent fluorescence lifetimes (20 to 1100 ps) indicate a stepwise formation of different conformers of the anions. The results reported here should be relevant to a better understanding of the photobehaviour of photochromic compounds and charged chromophores in biological systems.

Facile, sensitive and selective fluorescence turn-on detection of HSA/BSA in aqueous solution utilizing 2,4-dihydroxyl-3-iodo salicylaldehyde azine

A novel fluorescence turn-on detection method of human serum albumin (HSA) and bovine serum albumin (BSA) in aqueous solution is investigated using 2,4-dihydroxyl-3-iodo salicylaldehyde azine (DISA). Upon the addition of DISA to HSA/BSA solution, a fluorescence turn-on effect at 529 nm can be observed with a large stokes shift of approximately 129 nm based on hydrophobic binding-mode between protein and dye. Under the optimal condition, the linear ranges of fluorescence intensity for HSA and BSA are 0.1-30 microg mL(-1) with the relative correlation coefficient of R(2)=0.991 (n=10) and 0.3-50 microg mL(-1) with R(2)=0.997 (n=10); and the detection limits for HSA and BSA based on IUPAC (C(DL)=3S(b)/m) are 20 ng mL(-1) and 50 ng mL(-1), respectively.

Salicylaldehyde Azines as Fluorophores of Aggregation-Induced Emission Enhancement Characteristics

A series of salicylaldehyde azine derivatives were found to exhibit interesting aggregation-induced emission enhancement (AIEE) characteristics. In good solvent, all these compounds displayed very weak fluorescence, while strong emission was observed when they were placed in poor solvent. Moreover, the AIEE color of these compounds varied from green to red depending on the substituents on azines. Their in situ formation also promises potential applications in fluorescence sensing of hydrazine.

Spectroscopic and photophysical properties of salicylaldehyde azine (SAA) as a photochromic Schiff base suitable for heterogeneous studies

The photochromic cycle of the salicylaldehyde azine (SAA) has been investigated by means of the stationary and time-resolved UV–vis spectroscopy in a number of differently interacting solvents and micellar systems. The primary enol form of this Schiff base is much more energetically stabilized than in the other aromatic Schiff bases, which is reflected in remarkable resistance of SAA to the hydrolysis process. The fluorescence decay measured in highly viscous solvents as well as in micellar systems has proved the existence of different conformers of the cis-keto tautomer. Three different routes of the photochrome ( trans-keto tautomer) decay have been also observed.