Search Results (77)

This study details how 3-(naphthalen-2-yl)-1-phenylprop-2-en-1-one (3NPEO) behaves in terms of photophysics when exposed to different solvents. The solvatochromic effect study reveals significant polarity shifts in the excited states of the 3NPEO compound, likely due to an intramolecular proton transfer mechanism. Measurements of dipole moments provide insight into their resonance structures in both ground and excited states. Electrochemical analysis revealed a reversible redox process, indicating a favorable charge transport potential. HOMO and LUMO energies of the compound were computed via oxidation and reduction potential standards. 3NPEO exhibits optimal one-photon and two-photon absorption characteristics, validating its suitability for visible wavelength laser applications in photonic devices. Furthermore, molecular docking and dynamics simulations demonstrated strong interactions between 3NPEO and the progesterone receptor enzyme, supported by structure–activity relationship (SAR) analyses. In vitro cytotoxicity assays on the MDAMB-231 breast cancer cell line showed moderate tumor cell inhibitory activity. Apoptosis studies confirmed the induction of both early and late apoptosis. These findings suggest that 3NPEO holds promise as a potential anticancer agent targeting the progesterone receptor in breast cancer cells. Overall, the findings highlight the substantial influence of solvent polarity on the photophysical properties and the design of more effective and stable therapeutic agents. Full article

Excited state intramolecular proton transfer (ESIPT) within molecules in solvents plays important roles in photo-chemistry and photo-biology. Herein, the influence of 1-ethyl-3-methyl-imidazolium bis (trifluoromethylsulfonyl) imide ([EMIm][NTf₂]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF₆]) on the ESIPT of 4′-N,N-diethylamino-3-hydroxyflavone (DEAHF) was explored. The density functional theory and time-dependent density functional theory methodologies were used. The calculated fluorescence spectrum reveals that the fluorescence peaks of DEAHF in [EMIm][NTf₂] and [BMIm][PF₆] originate from the emission of N* and T* forms. The structure’s optimization, infrared spectra, non-covalent interactions and the scanning of potential energy curves collectively demonstrate that the ESIPT of DEAHF likely happen more in [EMIm][NTf₂] than in [BMIm][PF₆]. The solvation effects in [BMIm][PF₆] exhibit greater prominence compared to those in [EMIm][NTf₂], as evidenced by the free energy curve. The alterations in dipole moment indicate a substantial solvation relaxation during the ESIPT processes. Our aforementioned research offers backing for the advancement of novel fluorescent probes. Full article

Using 5-methyl salicylaldehyde (2) as a reactant to react with different amines, 2-aminobenzimidazole (1a), 2-aminobenzothiazole (1b), and 2-aminopyridine (1c), respectively, three types of Schiff base fluorescent probes 3a–3c were designed and synthesized for selective detection of Al³⁺ in aqueous media. The structure of the compounds was acquired by ¹H NMR, ¹³C NMR, and X-ray single-crystal diffraction. Furthermore, their photochromic and fluorescent behaviors have been investigated systematically by fluorescence spectra. Compounds 3a–3c can exhibit high selectivity, sensitivity, and anti-interference properties towards Al³⁺ in aqueous media. Among them, the limit of detection (LOD) of probe 3b for Al³⁺ is 2.81 × 10⁻⁷ M. Notably, the response times of probes 3a–3c for Al³⁺ are 90 s, 80 s, and 80 s, respectively, which are much faster than most previously reported probes. The coordination stoichiometry between compounds 3a–3c and Al³⁺ has been verified to be 1:1 through the Job’s plot. After coordination with Al³⁺, the C=N isomerization of compounds 3a–3c is inhibited, leading to the closure of the excited state intramolecular proton transfer (ESIPT) effect. At the same time, the fluorescence intensity is significantly increased through chelation-enhanced fluorescence mechanism (CHEF), which is confirmed by density functional theory (DFT) calculations. In addition, probes 3a–3c can be potentially applied in the selective and high-precision detection of Al³⁺ in environmental systems. Full article

Stroke, primarily ischemic (85%), results from inadequate blood supply and is worsened by ferroptosis, characterized by free radical generation and lipid peroxidation. Monitoring ferroptosis is essential for understanding its mechanisms and developing treatments. Glutathione (GSH) is a key ferroptosis biomarker, but current probes are limited by short excitation/emission wavelengths, small Stokes shifts, and inability to monitor dynamic GSH changes at the cellular membrane, where ferroptosis plays a crucial role. To address these issues, we developed the PM-Red-GSH, a novel near-infrared (NIR) probe based on the Excited-state intramolecular proton transfer (ESIPT) mechanism. It shows strong NIR emission (715 nm), large Stokes shift (290 nm), and enhanced membrane binding (PCC = 0.95) due to its alkyl group. PM-Red-GSH enables dynamic GSH monitoring in an MCAO mouse model. These findings offer new insights into ferroptosis and stroke treatment. Full article

There is currently a growing interest in imino derivatives of compounds such as thiadiazoles and other groups of compounds whose extended π-electron systems enhance their photophysical properties. These compounds also show low toxicity and strong antifungal activity, making them effective against fungal pathogens in crops. For the above reasons, in the first part of the paper, the structure of the selected analogs was considered, and detailed spectroscopic analyses were conducted focusing on the excited state intramolecular proton transfer (ESIPT) process taking place in the same. Measurements were taken in terms of absorption spectroscopy and electron fluorescence, synchronous spectra, and fluorescence lifetimes, as well as calculations of fluorescence quantum efficiency in selected solvents and concentrations. In the spectral observations, the ESIPT process was manifested in several solvents as very distinct dual fluorescence. Moreover, in selected molecules, this phenomenon was strongly related to molecular aggregation, which was associated with not very efficient but nonetheless visible fluorescence of the AIE (Aggregation-Induced Emission) type. In the second part of the paper, a detailed preliminary study is presented exploring the microbiological properties of selected imino-1,3,4-thiadiazole derivatives in the context of their potential applicability as inhibitors affecting the development and growth of some of the most important fungal pathogens attacking cereal crops and posing an increasing threat to modern agriculture. Overall, the research presented in this article provides a detailed, experimental analysis of the spectroscopic properties of selected imino-thiadiazoles and points to their potential use as novel and effective solutions capable of limiting the growth and development of fungal pathogens in cereals. Full article

Biomarker detection is imperative in the realms of modern medicine, biology, and environmental science, owing to the numerous avenues for its application. The recent scientific upsurge in the development of molecules, materials, and mechanisms for such scientific development has garnered considerable attention among scientists. In this connection, excited-state intramolecular proton transfer (ESIPT) properties of photoluminescent compounds provide considerable insights into the designing, development, and detection of biomarkers. ESIPT molecules significantly show a Stokes-shifted emission due to their sensitive nature and unique photophysical properties. Leveraging this photophysical property and tunable nature, several fluorescent probes of this genre can be designed and synthesized for a plethora of application spheres. Schiff bases encompass one such category of functional molecules displaying ESIPT properties, which can be mitigated by adding several other functionalities and desired optical characteristics. The current review article spans the basics of ESIPT properties of certain photoluminescent molecules and also envisages biosensing applications of recently developed imine–functionalized Schiff base molecules with such properties as the prima-foci, along with other applications. Full article

A novel fluorescent probe, Bibc-DNBS, based on the combination of the PET (photoinduced electron transfer) and ESIPT (excited-state intramolecular proton transfer) mechanisms, was designed and synthesized. Bibc-DNBS exhibited a Stokes shift of 172 nm in the fluorescence detection field. In addition, the probe exhibited good performance in key parameters in bioassays such as sensitivity, specificity, and response time. Based on these properties, Bibc-DNBS successfully monitored the biothiol levels in live cells and zebrafish models, providing an effective analytical tool for real-time monitoring of biothiols. More importantly, Bibc-DNBS could be useful for indirectly detecting β-lactamases. Bibc-DNBS(3-(1H-benzo[d]imidazol-2-yl)-4′-cyano-[1,1′-biphenyl]-4-yl2,4-dinitrobenzenesulfonate) facilitated the screening of β-lactamase inhibitors, using tazobactam and clavulanic acid as model compounds, with respective semi-inhibitory concentration values of 31.32 μM and 2.26 μM, respectively. It might also be applied to distinguish sensitive strain Staphylococcus aureus ATCC 29213 and drug-resistant strain Enterobacter cloacae ATCC 13047, which could provide strong support for the clinical application of antibiotics and the development of new drugs. Full article

The chalcone derivatives with hydroxy group (2) have been examined using low-temperature fluorescence spectroscopy. The study aimed to freeze the intramolecular charge transfer (ICT) motion in order to reveal the potential hidden transition(s) that are difficult to observe at room temperature. Although chalcone 2 revealed one emission peak at ~667 nm at room temperature, it exhibited two emission peaks (λ_em = 580 and 636 nm) in EtOH at liquid N₂ temperatures (77 K). With the aid of model compound 3 with methoxy group and aluminum complex 2-Al³⁺, attempts were made to assign these emission peaks. The results point towards the possibility of the coexistence of ICT and excited state intramolecular proton transfer (ESIPT) in the chalcone derivatives with extended conjugation. Full article

A series of colorful binuclear Schiff bases derived from the different diamine bridges including 1,2- ethylenediamine (bis-Et-SA, bis-Et-4-NEt₂, bis-Et-5-NO₂, bis-Et-Naph), 1,2-phenylenediamine (bis-Ph-SA, bis-Ph-4-NEt₂, bis-Ph-5-NO₂, bis-Ph-Naph), dicyano-1,2-ethenediamine (bis-CN-SA, bis-CN-4-NEt₂, bis-CN-5-NO₂, bis-CN-Naph) have been designed and prepared. The optical properties of these binuclear Schiff base ligands were fully determined by UV–Vis absorption spectroscopy, fluorescence emission spectroscopy, and time-dependent-density functional theory (TD-DFT) calculations. The inclusion of D-A systems and/or π-extended systems in these binuclear Schiff base ligands not only enables adjustable RGB light absorption and emission spectra (300~700 nm) but also yields high fluorescence quantum efficiencies of up to 0.84 in MeCN solution. Then, with the ESIPT (excited-state intramolecular proton transfer) property, fluorescence analysis showed that the probe bis-Et-SA and bis-Ph-SA could recognize Zn²⁺ via the “turn on” mode in the MeCN solution. During the detection process, bis-Et-SA and bis-Ph-SA demonstrate rapid response and high selectivity upon the addition of Zn²⁺. The coordination of Zn²⁺ with the oxygen atom and Schiff base nitrogen atom in a tetrahedral geometry is confirmed by Job’s plot, FT-IR, and ¹H NMR spectroscopy. In addition, the paper test and Hela cells were successfully carried out to detect Zn²⁺. Moreover, the sensitivity of bis-Et-SA and bis-Ph-SA is much better than that of those Schiff base ligands containing only one chelating unit [O^N^N^O]. Full article

Long-range proton transfer in several conjugated proton cranes, originating from 7-hydroxy quinoline as a proton transfer platform, has been investigated theoretically by means of DFT and TD-DFT methodology. Major emphasis was given to their applicability to provide clean switching upon irradiation. The border conditions require the existence of a single enol tautomer in the ground state, which under excitation through a series of consecutive exited and ground state intramolecular proton transfer steps is transferred to the keto tautomer. It was shown that the most suitable candidates are based on using iso-quinoline, pyrimidine and 4-nitropyridine as proton crane units. Their suitability is a function of aromaticity changes, the basicity of the nitrogen atom from the proton crane unit and the structural effects originating from their conjugation with 7-hydroxy quinoline. Full article

Excited-state intramolecular proton transfer (ESIPT) reactions are crucial in photoresponsive materials and fluorescent markers. The fluorescent compound 4-aminophthalimide (4-AP) has been reported to exhibit solvent-assisted ESIPT in protic solvents, such as methanol, wherein the solvent interacts with 4-AP to form a six-membered hydrogen-bonded ring that is strengthened upon excitation. Although the controversial observation of ESIPT in 4-AP has been extensively studied, the molecular mechanism has yet to be fully explored. In this study, femtosecond infrared spectroscopy was used to investigate the dynamics of 4-AP in methanol and acetonitrile after excitation at 350 and 300 nm, which promoted 4-AP to the S₁ and S₂ states, respectively. The excited 4-AP in the S₁ state relaxed to the ground state, while 4-AP in the S₂ state relaxed via the S₁ state without the occurrence of ESIPT. The enol form of 4-AP (Enol 4-AP) in the S₁ state was calculated to be ~10 kcal/mol higher in energy than the keto form in the S₁ state, indicating that keto-to-enol tautomerization was endergonic, ultimately resulting in no observable ESIPT for 4-AP in the S₁ state. Upon the excitation of 4-AP to the S₂ state, the transition to Enol-4-AP in the S₁ state was found to be exergonic; however, ESIPT must compete with an internal conversion from the S₂ to the S₁ state. The internal S₂ → S₁ conversion was significantly faster than the solvent-assisted ESIPT, resulting in a negligible ESIPT for the 4-AP excited to the S₂ state. The detailed excitation dynamics of 4-AP clearly reveal the molecular mechanism underlying its negligible ESIPT, despite the fact that it forms a favorable structure for solvent-assisted ESIPT. Full article

The effect of the external electric field on the ground-state tautomerism in 8-(benzo[d]thiazol-2-yl)quinolin-7-ol has been studied by using density functional theory. The compound exists as an enol tautomer (off state) and under the influence of the external electric field a long-range intramolecular proton transfer can occur, placing the tautomeric proton at the quinolyl nitrogen atom (on state). This is a result of the much higher dipole moment of the end keto tautomer and indicates that the external electric field can be used to mimic the implicit solvent effect in tautomeric systems. In the excited state, the further stabilization of the most polar on state leads to a situation when the excited-state intramolecular proton transfer becomes impossible, limiting the intramolecular rotation to the conical intersection region. Full article

A novel fluorescent probe containing an imine structure was synthesized through a condensation reaction based on the skeleton of antipyrine. Due to the synergistic effect of photoinduced electron transfer (PET), excited-state intramolecular proton transfer (ESIPT), and E/Z isomerization, the probe itself has weak fluorescence. When zinc ions are added to the ethanol solution of the probe, the formed complex inhibits PET, ESIPT, and E/Z isomerization while activating chelation-enhanced fluorescence (CHEF), resulting in fluorescent “turn-on” at 462 nm. Under optimal detection conditions, the probe can rapidly respond to zinc ions within 3 min, with a linear range of 60–220 μM and a lower limit of detection (LOD) of 0.63 μM. It can also specifically identify zinc ions in the presence of 13 common metal ions. Full article

Inspired by the outstanding nature of flavonoid derivatives in the fields of chemistry and medicine, in this work we mainly focus on exploring the photo-induced properties of the novel Et₂N-substituted flavonoid (ENF) fluorophore theoretically. Considering the potential photo-induced properties in different solvents and the chalcogen atomic electronegativity-associated photoexcitation, by time-dependent density functional theory (TDDFT) methods we primarily explore the intramolecular hydrogen bonding interactions and photo-induced charge redistribution behaviors. Via comparing geometrical data and the infrared (IR) spectral shifts-associated hydroxy moiety of ENF, we confirm that the intramolecular hydrogen bond O-H···O should be enhanced with facilitating an excited-state intramolecular proton-transfer (ESIPT) reaction. Particularly, the charge reorganization around hydrogen bonding moieties further reveals the tendency of ESIPT behavior. Combined with the construction of the potential energy surface and the search for reaction transition states, we finally confirmed the solvent-polarity-regulated behaviors as well as the chalcogen elements’ electronegativity-dependent ESIPT mechanisms for the ENF fluorophore. We sincerely wish our work could accelerate the further development and applications of flavonoid derivatives. Full article

DFT and TD-DFT were used in this article to investigate the effects of different substitutions at multiple sites on the photophysical mechanism of bis-HBX in the gas phase. Four different substitution modes were selected, denoted as A₁ (X=Me, Y=S), A₂ (X=OMe, Y=S), B₁ (X=Me, Y=NH), and C₁ (X=Me, Y=O). The geometric parameters proved that the IHBs enhanced after photoexcitation, which was conducive to promote the ESIPT process. Combining the analysis of the PECs, it was revealed that the bis-HBX molecule underwent the ESIPT process, and the ease of the ESIPT process was in the order of A₁ > A₂> B₁ > C₁. In particular, the TICT process in A₁ and B₁ promoted the occurrence of the ESIPT process. In addition, the IC process was identified, particularly in C₁. Meanwhile, the calculation of fluorescence lifetime and fluorescence rate further confirmed that A₁ was the most effective fluorescent probe molecule. This theoretical research provides an innovative theoretical reference for regulating ESIPT reactions and optimizing fluorescent probe molecules. Full article