Water sensitive fluorescence tuning of V-shaped ESIPT fluorophores: Substituent effect and trace amount water sensing in DMSO

Highly sensitive nature of excited state intramolecular proton transfer (ESIPT) functionality in organic fluorophores made them potential candidates for developing environmental sensors and bioimaging applications. Herein, we report the synthesis of V-shaped Dapsone based Schiff base ESIPT derivatives (1-3) and water sensitive wide fluorescence tuning from blue to red in DMSO. Solid-state structural analysis confirmed the V-shaped molecular structure with intramolecular H-bonding and substituent dependent molecular packing in the crystal lattice. 1 showed strong solid-state fluorescence (λmax = 554 nm, Φf = 21.2 %) whereas methoxy substitution (2 and 3) produced tunable but significantly reduced fluorescence (λmax = 547 (2) and 615 nm (3), Φf = 2.1 (2) and 6.5 % (3)). Interestingly, aggregation induced emission (AIE) studies in DMSO-water mixture revealed water sensitive fluorescence tuning. The trace amount of water (less than 1 %) in DMSO converted the non-emissive 1-3 into highly emissive state due to keto tautomer formation. Further increasing water percentage produced deprotonated state of 1-3 in DMSO and enhanced the fluorescence intensity with red shifting of emission peak. At higher water fraction, 1-3 in DMSO produced aggregates and red shifted the emission with reduction of fluorescence intensity. The concentration dependent fluorescence study revealed the very low detection limit of water in DMSO. The limit of detection (LOD) of 1, 2 and 3 were 0.14, 1.04 and 0.65 % of water in DMSO. Hence, simple Schiff bases of 1-3 showed water concentration dependent keto isomer, deprotonated and aggregated state tunable fluorescence in DMSO. Further, scanning electron microscopic (SEM) studies of 1-3 showed water concentration controlled self-assembly and tunable fluorescence.

Characterization of a Zeolite-Y-Encapsulated Zn(II)Salmphen Complex with Targeted Anticancer Property

Resistance and severe side effects of classical chemotherapeutic drugs are major challenges to cancer therapy. New therapeutic agents and combination therapy are considered potential solutions that enhance the efficacy of the drug as well as reduce drug resistance. The success of a platinum-based anticancer drug, cisplatin, has paved the way to explore metal-centered anticancer therapeutic agents. Herein, the zeolite-Y-encapsulated Zn(II)Salmphen complex is synthesized using a flexible ligand approach. The Zn(II)Salmphen complex and its encapsulation within the supercage of zeolite-Y were characterized by elemental analysis, Fourier transform infrared (FTIR) spectroscopy, UV-vis, fluorescence, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), NMR, and high-resolution mass spectrometry (HRMS) techniques. Elemental analysis, PXRD, and SEM, all together confirm the integrity of the zeolite framework after the encapsulation of Zn(II)Salmphen complex in it, and elemental analysis provides the Si/Al ratio and Zn content present. FTIR and XPS studies indicate the successful encapsulation of the complex. NMR and HRMS studies confirm that the Zn(II)Salmphen complex is dimer; however, within the supercage of zeolite-Y, it is expected to exist as a monomer. The extent of structural modification of the encapsulated Zn(II)Salmphen complex is intimated by electronic spectroscopic studies. The free-state Zn(II)Salmphen is a fluorescent complex, and even the encapsulated Zn(II)Salmphen complex, when taken in dimethyl sulfoxide (DMSO), shows fluorescence. In comparison to cisplatin, encapsulated Zn(II)Salmphen complex displays comparable cytotoxicity (IC50 = 2.0 ± 0.5 μg/mL at 48 h) toward breast cancer cell line, whereas free Zn(II)Salmphen has better cytotoxicity (IC50 = 1.5 ± 0.5 μg/mL at 48 h). Importantly, elemental analysis has revealed that the IC50 value, if calculated only in terms of Zn(II)Salmphen within Zn(II)Salmphen-Y, is as low as 54.59 ng/mL, indicating a very high efficacy of the drug. Interestingly, a 48 h treatment with the encapsulated Zn(II)Salmphen complex shows no toxicity toward immortal noncancerous keratinocyte cells (HaCaT), whereas cisplatin has an IC50 value of 1.75 ± 0.5 μg/mL. Internalization studies indicate that zeolite-Y targets cancer cells better than it does noncancerous ones. Hence, cellular uptake of the zeolite-encapsulated Zn(II)Salmphen complex in cancer cells is more than that in HaCaT cells, resulting in the generation of more reactive oxygen species and cell death. Significant upregulation of DNA damage response protein indicates that DNA-damage-induced cellular apoptosis could be the mechanism of drug action. Overall, the zeolite-encapsulated Zn(II)Salmphen complex could be a better alternative to the traditional drug cisplatin with minimal effect on noncancerous HaCaT cells and can also be utilized as a fluorescent probe in exploring the mechanistic pathway of its activity against cancer cells.

Comprehensive Empirical Model of Substitution—Influence on Hydrogen Bonding in Aromatic Schiff Bases

In this work, over 500 structures of tri-ring aromatic Schiff bases with different substitution patterns were investigated to develop a unified description of the substituent effect on the intramolecular hydrogen bridge. Both proximal and distal effects were examined using Density Functional Theory (DFT) in the gas phase and with solvent reaction field (Polarizable Continuum Model (PCM) and water as the solvent). In order to investigate and characterize the non-covalent interactions, a topological analysis was performed using the Quantum Theory of Atoms In Molecules (QTAIM) theory and Non-Covalent Interactions (NCI) index. The obtained results were summarized as the generalized, empirical model of the composite substituent effect, assessed using an additional group of simple ring-based Schiff bases. The composite substituent effect has been divided into separate increments describing the different interactions of the hydrogen bridge and the substituent: the classical substituent effect, involving resonance and induction mediated through the ring, steric increment based on substituent proximity to the bridge elements, and distal increment, derived from substitution on the distal ring.

Fashionable Co-operative Sensing of Bivalent Zn2+ and Cd2+ in Attendance of OAc- by Use of Simple Sensor: Exploration of Molecular Logic Gate and Docking Studies

The Schiff-base probe H₂VL [6,6'-((1E,1'E)-hydrazine-1,2 diylidenebis(methanylylidene))bis(2-methoxyphenol)] is synthesized and structurally characterized by single crystal X-ray diffraction (SCXRD). H₂VL is able to detect selectively acetate ion (OAc-) colorimetrically over other anions with 1:1 co-ordination. The detection limit is found to be 4.93 µM. On the other hand, fluorescence intensity of the receptor is drastically enhanced with Zn²⁺ and Cd²⁺ in the presence of acetate as counter anion. N, N-Dimethyl formamide (DMF) or Dimethylsulphoxide (DMSO) and acetate (OAc-) was the best solvent and counter anion for Zn²⁺/Cd²⁺ -sensing compared with other solvents and anions, respectively. Detection limit for Zn²⁺ and Cd²⁺ are calculated to be 1.94 µM and 1.99 µM, respectively. The strong selective emissive behavior could be attributed to the CHEF (chelation-enhanced fluorescence) process. According to the changes in output emission intensity in DMSO in response to the set of ions (Zn²⁺, Cd²⁺ and OAc¯) as input variables, the function of 3-input multifunctional molecular logic circuits has been demonstrated. The molecular docking studies of H₂VL with DNA and BSA are also performed to confirm its possible bioactivity.

The crystal structure of 2,2′-((1E,1′E)-hydrazine-1,2-diylidenebis(methaneylylidene))bis(4-chlorophenol), C14H10Cl2N2O2

C14H10Cl2N2O2, triclinic, P 1 ‾ $P\bar{1}$ (no. 2), a = 6.165(12) Å, b = 7.192(13) Å, c = 7.829(15) Å, α = 74.97(2)°, β = 81.92(2)°, γ = 79.84(2)°, V = 328.3(11) Å3, Z = 1, R gt (F) = 0.0312, wR ref (F 2) = 0.0859, T = 296(2) K.

A Family of Ethyl N-Salicylideneglycinate Dyes Stabilized by Intramolecular Hydrogen Bonding: Photophysical Properties and Computational Study

In this work we report solvatochromic and luminescent properties of ethyl N-salicylideneglycinate (1), ethyl N-(5-methoxysalicylidene)glycinate (2), ethyl N-(5-bromosalicylidene)glycinate (3), and ethyl N-(5-nitrosalicylidene)glycinate (4) dyes. 1–4 correspond to a class of N-salicylidene aniline derivatives, whose photophysical properties are dictated by the intramolecular proton transfer between the OH-function and the imine N-atom, affording tautomerization between the enol-imine and keto-enamine forms. Photophysical properties of 1–4 were studied in different pure non-polar and (a)protic polar solvents as well as upon gradual addition of NEt₃, NaOH, and CH₃SO₃H. The DFT calculations were performed to verify the structures of 1–4 as well as their electronic and optical properties.

The crystal structure of 6,6′-((1E,1′E)-hydrazine-1,2-diylidenebis(methaneylylidene)) bis(2-bromo-4-nitrophenol) — dimethylsulfoxide (1/2), C14H8Br2N4O6⋅2(C2H6OS)

C14H8Br2N4O6⋅2(C2H6OS), triclinic, P 1 ‾ $P\bar{1}$ (no. 2), a = 6.1463(12) Å, b = 8.3637(16) Å, c = 12.461(3) Å, α = 85.578(5)°, β = 85.942(5)°, γ = 86.310(5)°, V = 635.9(2) Å3, Z = 1, R gt (F) = 0.0601, wR ref (F 2) = 0.0983, T = 296 K.

CCDC no.: 2057510

Resonance Assisted Hydrogen Bonding Phenomenon Unveiled through Both Experiments and Theory: A New Family of Ethyl N-Salicylideneglycinate Dyes

Extensive experimental and theoretical investigations are reported on the nature of resonance-assisted hydrogen bonding phenomenon (RAHB) and its influence on photophysical properties of the newly designed dyes differing in donor-acceptor properties, namely ethyl N-salicylideneglycinate (1), ethyl N-(5-methoxysalicylidene)glycinate (2), ethyl N-(5-bromosalicylidene)glycinate (3) and ethyl N-(5-nitrosalicylidene)glycinate (4). All compounds are thermochromic in the solid state and they contain a typical intramolecular O-H⋅⋅⋅N hydrogen bond formed between the hydroxyl hydrogen atom and the imine nitrogen atom, yielding the enol form in the solid state. It is unveiled, that the magnitude of RAHB effect fine tunes the strength of the O-H⋅⋅⋅N bonding and accordingly the relative populations of the enol, cis-keto and trans-keto forms leading to variation of the photophysical properties of 1-4. It is determined, that the electron-withdrawing NO₂ in 4 amplifies the most RAHB effect causing the breaking of the O-H⋅⋅⋅N hydrogen bond and accordingly formation of the dominant cis-keto isomer in both the solid state and EtOH. To this end, the UV/Vis spectra of 1-3 in EtOH revealed the exclusive presence of the enol form, while the prevalent contribution of the cis-keto form was found for 4. Furthermore, only compound 4 is emissive in the solid state in ambient condition due to dual emission arising from the cis-keto* and trans-keto* forms, while 2 was found to be highly emissive in EtOH. It is revealed qualitatively and quantitatively, based on the ETS-NOCV charge and energy decomposition scheme and the EDDB population-based method, that RAHB is strongly a non-local phenomenon based on electrons pumping or sucking through both the π- and σ-channels, which accordingly exerts chemical bonding changes at both the phenyl ring and predominantly a distant O-H⋅⋅⋅N area.

Seed-triggered solid-to-solid transformation between color polymorphs: striking differences between quasi-isomorphous crystals of dichloro-substituted salicylideneaniline regioisomers

The title compound exhibited two color polymorphs, of which the yellow form transformed to the orange form during heating, and this peculiar phase transition behavior was explained in relation to the pseudo-symmetry of its molecular structure.

A unique benzimidazole-naphthalene hybrid molecule for independent detection of Zn2+ and N3- ions: Experimental and theoretical investigations

Single crystal X-ray structurally characterized benzimidazole-naphthalene hybrid (NABI) functions as a unique dual analyte sensor that can detect Zn²⁺ cation and N₃^- anion independently. The NABI forms chelate with Zn²⁺ to inhibit internal charge transfer (ICT) and CHN isomerisation resulting chelation enhanced fluorescence (CHEF). On the other hand, the sensing of N₃^- is based on formation of supramolecular H-bonded rigid assembly. The association constant of NABI for Zn²⁺ and N₃^- ions are 19 × 10⁴ M^-1 and 11 × 10² M^-1, respectively. Corresponding limit of detections (LOD) are 6.85 × 10^-8 and 1.82 × 10^-7 M, respectively. NABI efficiently detects intracellular Zn²⁺ and N₃^- ions with no cytotoxicity on J774A.1cells under fluorescence microscope. DFT studies unlock underlying spectroscopic properties of free NABI and Zn²⁺/N₃^- bound forms.

Gels with sense: supramolecular materials that respond to heat, light and sound

Advances in the field of supramolecular chemistry have made it possible, in many situations, to reliably engineer soft materials to address a specific technological problem. Particularly exciting are "smart" gels that undergo reversible physical changes on exposure to remote, non-invasive environmental stimuli. This review explores the development of gels which are transformed by heat, light and ultrasound, as well as other mechanical inputs, applied voltages and magnetic fields. Focusing on small-molecule gelators, but with reference to organic polymers and metal-organic systems, we examine how the structures of gelator assemblies influence the physical and chemical mechanisms leading to thermo-, photo- and mechano-switchable behaviour. In addition, we evaluate how the unique and versatile properties of smart materials may be exploited in a wide range of applications, including catalysis, crystal growth, ion sensing, drug delivery, data storage and biomaterial replacement.

Structure and electronics in dimeric boron π expanded azine and salphen complexes

Although boron-based fluorophores incorporating nitrogenous chelating ligands have received much attention, there has been little work on examples of boron-salphen and azine derivatives. In this report, we present several π expanded boron salphen type complexes, incorporating both bis(2-hydroxynaphthaldehyde)azine as well as ortho, meta and para variants of the analogous 2-hydroxynaphthaldehyde salphen compounds. For the azine, we observed only the formation of a single BF₂ adduct, while for the naphth-phen compounds dimeric BF₂ binding was observed. All new compounds were fully characterized via X-ray diffraction, and both DFT and TDDFT studies were carried out to probe the electronic structures of these fluorophores.

C–H⋯Br–C vs. C–Br⋯Br–C vs. C–Br⋯N bonding in molecular self-assembly of pyridine-containing dyes

We have studied N-(5-bromosalicylidene)-x-aminopyridine dyes (x = 2, 1; 3, 2; 4, 3) by means of single crystal X-ray diffraction and Hirshfeld surface analysis. Their optical properties were also examined and correlated with structural findings.

Crystal structure of 2-{[(E)-(4-anilinophen-yl)iminium-yl]meth-yl}-5-(di-ethyl-amino)-phenolate

The title compound, C₂₃H₂₅N₃O, crystallized with one single mol­ecule in the asymmetric unit and present in the zwitterionic form. In the crystal, mol­ecules are connected by N—H⋯O hydrogen bonds generating –A–B–A–B– zigzag chains extending along [010]. The chains are linked via C—H⋯π inter­actions and π–π inter­actions [with a centroid–centroid distance of 3.444 (3) Å)] between the benzene ring and the imino group of symmetry-related mol­ecules, forming slabs lying parallel to (100).

The title compound, C₂₃H₂₅N₃O, crystallized with one single mol­ecule in the asymmetric unit and is present in the zwitterionic form. There is an intra­molecular N—H⋯O hydrogen bond in the mol­ecule with the phenol ring being inclined to the central benzene ring by 20.67 (14)°. The terminal amino­phenyl ring forms a dihedral angle of 54.21 (14)° with the central benzene ring. The two outer aromatic rings are inclined to one another by 74.54 (14)°. In the crystal, the mol­ecules are connected by N—H⋯O hydrogen bonds, with adjacent molecules related by a 2₁ screw axis, generating –A–B–A–B– zigzag chains extending along [010]. The chains are linked via C—H⋯π and π–π inter­actions [with a centroid–centroid distance of 3.444 (3) Å] between the benzene ring and the imino group of symmetry-related mol­ecules, forming slabs lying parallel to (100).

Photoluminescence and labelling for microcrack bone of N-salicylidene-3-amino-1,2,4-triazole

A new Schiff base of N-salicylidene-3-amino-1,2,4-triazole (SAT) was synthesized and its photoluminescent, photochromic and thermochromic properties were characterized and demonstrated. The fluorescence lifetime and quantum yield of SAT were measured and the microcrack bone imaging using SAT as a fluorescent label was observed by laser scanning confocal microscope (LSCM). The absorption spectrum of SAT was demonstrated using DFT/TD-DFT calculation.

Crystal structure of (E)-2-{[(4-anilinophen-yl)imino]-meth-yl}phenol

The title compound crystallized with two independent mol­ecules (A and B) in the asymmetric unit, which differ essentially in the orientation of the terminal amino­phenyl ring with respect to the central benzene ring. In the crystal, mol­ecules are linked via N—H⋯O hydrogen bonds forming –A-B–A–B– zigzag chains propagating along [010].

The title compound, C₁₉H₁₆N₂O, crystallized with two independent mol­ecules (A and B) in the asymmetric unit. There is an intra­molecular O—H⋯N hydrogen bond in each mol­ecule with the phenol ring being inclined to the central benzene ring by 4.93 (14) and 7.12 (14)° in mol­ecules A and B, respectively. The conformation of the two mol­ecules differs essentially in the orientation of the terminal amino­phenyl ring with respect to the central benzene ring; this dihedral angle is 50.51 (4)° in mol­ecule A and 54.61 (14)° in mol­ecule B. The two outer aromatic rings are inclined to one another by 51.39 (14) and 49.88 (14)° in mol­ecules A and B, respectively. In the crystal, mol­ecules are connected by N—H⋯O hydrogen bonds generating –A-B–A–B– zigzag chains extending along [010]. The chains are linked via C—H⋯π inter­actions involving neighbouring A mol­ecules, forming slabs lying parallel to (100).

N-Salicylidene aniline derivatives based on the N′-thiophosphorylated thiourea scaffold

A new family of thermochromic N′-thiophosphorylated thiourea-containing N-salicylidene aniline derivatives (anils) of the common formula 6-{(2-OH-aryl)–CHN}-Py-2-NHC(S)NHP(S)(OiPr)₂ has been synthesized by the condensation of N-thiophosphorylated thiourea 6-NH₂-Py-2-NHC(S)NHP(S)(OiPr)₂ with the corresponding salicylaldehyde.

From a mononuclear Ni(II) precursor to antiferromagnetically coupled trinuclear double-stranded helicates

Reaction of the mononuclear Ni(II) complex [Ni{2-Py(6-NH2)NHC(S)NP(S)(OiPr)2}2] with different salicylaldehydes leads to new antiferromagnetically coupled trinuclear double-stranded helicates , where Ni(II) metal ions are coordinated by two bis-anionic thiourea ligands and two deprotonated molecules of the corresponding aldehyde.