Meta Position Research Articles

Oxindole derivatives alleviate paracetamol-induced nephrotoxicity and hepatotoxicity: biochemical, histological, and computational expressions.

Oxindole is a nature-derived heteroaromatic nucleus with a history of preclinical uses in various conditions. In this study, oxindole derivatives, 6-chloro-3-(3-hydroxybenzylidene) indolin-2-one (3OH) and 6-chloro-3-(4-hydroxybenzylidene) indolin-2-one (4OH) were evaluated for nephroprotective and hepatoprotective effects. Paracetamol-induced nephrotoxicity and hepatotoxicity model was used in mice. Tissue histology and serum biochemistry were carried out to further support in vivo activity. Compound 3OH reduced serum urea and creatinine levels by 51.8% and 64.6%, respectively (p < 0.0001). Excretion of creatinine by 3OH 10mg was 52.8% as compared to silymarin. In case of urinary excretion of urea, the significant rise in excretion was observed in 4OH 15mg (30.4%; p < 0.05) and 3OH 10mg group (29.24%; p < 0.05). The compound 3OH exhibited restorative pattern of the renal tissues with slight inflammatory infiltrations. In case of hepatoprotective activity, 3OH reduced (59.9%; p < 0.0001) serum ALT at 5mg even more than silymarin and all other doses of oxindole derivatives. In case of serum AST, all treatment groups produced significant (p < 0.0001) reduction except 3OH 15mg.Computational studies supported the results as both derivatives were found to have promising interactions with enzymes at lower binding energies. Compound 3OH which possesses a hydroxyl group based on aromatic ring at meta position was the most successful drug candidate throughout this study. In a nutshell, the selected compounds elicited significant nephroprotective and hepatoprotective-like effects in mice.

Spin Mixing in Intramolecular Singlet Fission: A First-Principles-Based Quantum Dynamical Study.

We investigate the dynamical interplay between the different triplet-pair spin states that are formed in the intramolecular singlet fission process in a series of pentacene-based dimers covalently bonded to a phenylene linker in ortho, meta, and para positions. Using first-principles calculations and a density matrix quantum dynamical approach we show that the spin dipole-dipole interaction leads to significant population of the quintet spin manifold in these regioisomers when the singlet, triplet and quintet triplet-pair states are quasidegenerate. Furthermore, we also show that the relative arrangement of the pentacene-like moieties has a profound impact on the dynamics of the spin-mixing process, affecting both the relative population of the different spin-states involved in the dynamics and the time scale of the process.

Design And Synthesis Of Novel Thiazole Linked Tetrahydropyridine Analogues As Anticancer Agents.

A library of new thiazole linked tetrahydropyridines (6a-q) synthesized and screened for their invitro anticancer activity against human breast adeno carcinoma cell viz. MCF-7 and MDA-MB-231. The two compounds 6d containing -F and -Cl functions in para and meta position of phenyl ring (9.94 ± 1.02µM, 9.78 ± 1.08µM) and 6e with -Cl and -NH2 functions on pyridine ring (9.72 ± 0.91 µM,9.54 ± 0.95µM) demonstrated outstanding activity against both the cell lines when compared to Doxorubicin. The benzofuran analogue 6o presented good activity with an IC50 value of 12.19 ± 1.03µM (MCF-7) and 12.22 ± 1.07µM (MDA-MB-231). The molecular docking study of potent molecule 6e against crystal structure of breast tumor kinase presented promising docking score and binding interactions. Predicted pharmacokinetics properties of compounds 6a-q and presented boiled diagram of compounds 6d and 6e implied favourable drug-likeness properties.

Synthesis of 1,3,5-trisubstituted 1,2,4-triazoles enabled by a gold-catalyzed three-component reaction

Valuable fully substituted 1,2,4-triazoles are obtained via a gold-catalyzed three-component reaction involving ethyl diazoacetate, aryldiazonium salts, and nitriles. The reaction proceeds under mild conditions, is regioselective, and allows the introduction of mono- and di-substituted aryl rings at the ortho, meta, and para positions. Mechanistic evidence suggests the participation of Au(III) species as the active catalysts.

A theoretical investigation into the impact of solvents (alkanolic and non-alkanolic), structural and spectroscopic properties, donor-acceptor insights, Hirshfeld surface, and molecular docking of the anti-tumor compound (2E)-3-[4-(dimethylamino)phenyl]-1-(3-nitrophenyl)prop-2-en-1-one

In this study, computational methods were employed to analyze the molecular structure of (2E)-3-[4-(Dimethylamino)phenyl]-1-(3-nitrophenyl)prop-2-en-1-one (DMAPNP), investigating its structural and spectroscopic properties along with its biological activity. In particular, the Frontier Molecular Orbital (FMO) and Molecular Electrostatic Potential (MEP) surfaces in alkanolic solvents (ethanediol, ethanol, and methanol) and non-alkanolic solvents (DMSO, toluene, and water) were generated to analyze the solvent-solute interactions. The H→L transition shows low oscillator strengths (0.0002 in toluene to 0.0013 in ethanediol, DMSO, and water), indicating limited significance in the absorption spectrum. In contrast, the H→L+1 transition has much higher oscillator strengths, around 0.9412 for ethanediol and 0.9385 for DMSO and toluene, suggesting a greater likelihood of absorption at these wavelengths. The simulated vibrational wavenumbers revealed the presence of CH, NO2, CN, CC, CH3, and C=O groups in DMAPNP. The calculated chemical shifts confirmed the molecular structure of DMAPNP and aligned with standard values. In Hirshfeld surface analysis, the crystal packing of DMAPNP was primarily stabilized by H…H interactions, contributing 41.3%, followed by O…H / H…O interactions at 30.9%. In Natural Bond Orbital (NBO) analysis, the interaction between C20-H38 and C15-H33 shows a stabilization energy of 1102.89 kJ/mol, highlighting σ-σ* transitions. In contrast, the C12-C16 and C15-H33 interactions exhibit a stabilization energy of 2542.16 kJ/mol, indicating substantial π-σ* contributions. In the Mulliken charge distribution, the carbon atoms C18 (-1.33704e) and C13 (1.776064e), located in the para and meta positions concerning the nitro group (NO2), exhibit the highest positive and negative potentials, respectively. Molecular docking assessed DMAPNP as a potential anti-tumor agent by inhibiting the key regulatory enzyme fructose-2,6-bisphosphatase, with a binding energy of -8.13 kcal/mol.

Positional Isomerism Toward Tunable Organic Afterglow and Reversible Photoactivation Behavior for Anti‐Counterfeiting and Encryption

AbstractAchieving amorphous polymers with ultralong room‐temperature phosphorescence (RTP), tunable organic afterglow, and reversible photoactivation behavior is highly desirable for practical applications but challenging. Herein, simple positional isomers with three carboxyl groups located in the ortho, meta, and para positions of the triphenylamine skeleton are designed and synthesized. By physically blending with the poly(vinyl alcohol) matrix, these isomers show ultralong RTP properties, among which the meta‐isomer has the longest RTP lifetime (620.1 ms). Theoretical calculations reveal that the more efficient intersystem crossing, the slower radiative decay rate of the lowest triplet excitons, and stronger intermolecular hydrogen‐bonding interactions should be responsible for the superior RTP property of meta‐isomer. Furthermore, the tunable organic afterglow is readily realized via a triplet‐to‐singlet energy transfer process. More impressively, the meta and para isomers exhibit reversible photoactivated ultralong RTP properties after embedding into the rigid poly(methyl methacrylate) matrix. Finally, amorphous and flexible polymer films prepared from these positional isomers show potential applications in advanced anti‐counterfeiting and multilevel encryption through subtly combining ultralong RTP lifetime, tunable organic afterglow, and reversible photoactivation behavior.

Computational exploration of novel ketoprofen derivatives: Molecular dynamics simulations and MM-PBSA calculations for COX-2 inhibition as promising anti-inflammatory drugs

Computer-aided drug design is widely employed to identify novel compounds for therapeutic applications. Ketoprofen (KTP), a commonly used and marketed nonsteroidal anti-inflammatory drug (NSAID), is effective in treating pain, fever, inflammation, and some cancers. In this research, we explored the behavior of six analogues designed by structurally modifying the KTP molecule. Specifically, KTP-A and KTP-B contain a –CN group at the ortho position, KTP-C and KTP-D have a –CN group at the meta position, and KTP-E and KTP-F feature a –CF3 group at the meta position. To assess these analogues, we conducted molecular dynamics simulations (MD) to study their inhibitory effects on human cyclooxygenase 2 (COX-2), providing detailed insights into the structure and dynamics of the protein both with and without ligands. MD simulation, enhanced by technological advances, has proven to be a powerful tool for new drug discovery. We further quantified the binding affinity of these drug molecules toward COX-2 using molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) binding free energy calculations. The dynamic properties were evaluated through analyses of root mean square deviations (RMSD), root mean square fluctuations (RMSF), radius of gyration (Rg), solvent-accessible surface area (SASA), covariance matrix, principal component analysis (PCA), and Gibbs free energy landscapes (FEL). Ultimately, this study confirms that the six KTP derivatives are promising candidates for the treatment of inflammation, with KTP-B standing out as particularly effective.

Benzimidazolium salts bearing ester group: Synthesis, characterization, crystal structure, molecular docking studies, and inhibitory properties against metabolic enzymes

In this work, the synthesis of several unsymmetrical benzimidazolium salts with an ester (2-ethoxy-2-oxoethyl) group on the nitrogen atom is described. The structures of all compounds were fully characterized by spectroscopic (1H, 13C NMR, FTIR) and analytical (elemental analysis) methods. However, single-crystal X-ray diffraction analysis elucidated the molecular and crystal structures of compounds 1a and 1c. Asymmetric units of both crystal structures contain two crystallographically independent molecules and two bromide anions. All compounds exhibited substantial inhibition against the cytosolic carbonic anhydrase isoforms (hCA I and hCA II) and acetylcholinesterase (AChE) with Ki values 51.00–45.18 nM, 46.94–305.65 nM, and 17.57–65.68 nM, respectively. Notably, compound 1d showed extreme inhibitory effect against hCA I with 51.00±5.31 nM (AZA: 275.44±13.32 nM), hCA II with 46.94±5.44 nM (AZA: 236.55±17.88 nM) and AChE with 17.57±3.14 nM (TAC: 80.44±6.88 nM). In silico approach showed that compound 1d could form stable complexes with target enzymes with a different binding affinity (BE:9.01 kcal/mol for AChE; -7.22 kcal/mol for hCA II and -6.51 kcal/mol for hCA I). The results supported the medical potential of benzimidazolium salts containing ester group. They significantly lighted our knowledge about the chemistry of side groups on phenyl ring especially in the para position as compared to ortho and meta positions.

Hybrid Analogues of Hydrazone and Phthalimide: Design, Synthesis, In vivo, In vitro, and In silico Evaluation as Analgesic Agents.

Based on the anti-inflammatory and analgesic activity of hydrazone and phthalimide, a new series of hybrid hydrazone and phthalimide pharmacophores was prepared and evaluated as analgesic agents. The designed ligands were synthesized by reaction of the appropriate aldehydes and 2- aminophthalimide. Analgesic, cyclooxygenase inhibitory, and cytostatic activity of prepared compounds were measured. All the tested ligands demonstrated significant analgesic activity. Moreover, compounds 3i and 3h were the most potent ligands in the formalin and writhing tests, respectively. Compounds 3g, 3j, and 3l were the most COX-2 selective ligands and ligand 3e was the most potent COX inhibitor with a 0.79 of COX-2 selectivity ratio. The presence of electron-withdrawing moieties with hydrogen bonding ability at the meta position was found to affect the selectivity efficiently, in which compounds 3g, 3l, and 3k showed high COX-2 selectivity, and compound 3k was the most potent one. The cytostatic activity of selected ligands demonstrated that compounds 3e, 3f, 3h, 3k, and 3m showed good analgesic and COX inhibitory activity and were less toxic than the reference drug. High therapeutic index of these ligands is one of the valuable advantages of these compounds.

First Principle Investigations of Structural, Electronic and Thermal Properties of Pristine, Metal and Non-Metal Doped Silicene for Thermoelectric Applications

Silicene, a two-dimensional hexagonal silicon layer, exhibits exceptional electronic and thermoelectric properties. However, its application in semiconductors is hindered by its zeroband gap, which could be overcome by modifying its electronic properties through doping. In this paper, Density Functional Theory (DFT) calculations were performed to investigate the band gap opening in silicene by studying the effect of magnesium and sulphur doping on its electronic, structural and thermal properties. Pristine silicene has a lattice constant of 3.86 Å and a zero-band gap. Upon doping with 12.5% S and Mg atoms, the lattice constant modifies to 3.45 Å and 3.93 Å, respectively, resulting in a direct band gap opening. For 25% Mg and S doping, the result shows that Mg and S effectively alter the band structure and the band gap of silicene monolayer at various configurations. The maximum band gap was 0.98 eV and 1.22 eV for Mg and S doping into the meta position to the reference point R, respectively. The power factor significantly increases with doping, reaching 1.20 x 1011 WK-2m-1 and 1.40 x 1011 WK- 2 m-1 for 12.5% Mg and S doping compared to 7.4 x 1010 WK-2m-1 for pristine silicene. This substantial enhancement indicates improved thermoelectric performance, making silicene a promising candidate for thermoelectric applications. Results demonstrate that tuning the band gap through doping can simultaneously enhance the power factor, highlighting the potential of Mg/S-doped silicene for efficient energy harvesting and conversion.

Chiral Bis(binaphthyl) Cyclopentadienyl Ligands for Rhodium-Catalyzed Desymmetrization of Diarylmethanes via Selective Arene Coordination.

Owing to substantial advances in the past several decades, transition-metal-catalyzed asymmetric reactions have garnered considerable attention as pivotal methods for constructing chiral molecules from abundant, readily available achiral counterparts. These advances are largely attributed to the development of chiral ligands that control stereochemistry through steric repulsion and other noncovalent interactions between the ligands and functional groups or prochiral centers on the substrates. However, stereocontrol weakens dramatically with increasing distance between the reaction site and the functional group or prochiral center. Herein, we report a symphonic strategy for remote stereocontrol of Rh(III)-catalyzed asymmetric benzylic C-H bond addition reactions of diarylmethanes in which the two aryl motifs differ at the meta and/or para position. Specifically, catalysts bearing a new type of chiral cyclopentadienyl (Cp) ligand differentiate between the two aromatic rings of the diarylmethane by arene-selective η6 coordination, setting up an opportunity for ligand-controlled stereoselective benzylic deprotonation and subsequent stereoselective addition to the 1,1-bis(arylsulfonyl)ethylene.

Design and synthesis of a 2,5-Diarylthiophene chromophore for enhanced near-infrared two-photon uncaging efficiency of calcium ions

The design and synthesis of two-photon-responsive chromophores have recently garnered significant attention owing to their potential applications in materials and life sciences. In this study, a novel π-conjugated system, 2-dimethylaminophenyl-5-nitrophenylthiophene derivatives, featuring a thiophene unit as the π-linker between the donor (NMe2C6H4–) and acceptor (NO2C6H4–) units was designed, synthesized, and applied for the development of two-photon-responsive chromophores as a photoremovable protecting group in the near-infrared region. Notably, the positional effect of the nitro group (NO2), meta versus para position, was observed in the uncaging process of benzoic acid. Additionally, while the para-isomer exhibited a single fluorescence peak, a dual emission was detected for the meta-isomer in polar solvents. The caged calcium ion (Ca2+) incorporating the newly synthesized thiophene unit exhibited a sizable two-photon absorption cross-section value (σ2 = 129 GM at 830 nm). Both one-photon and two-photon photoirradiation of caged calcium ions successfully released calcium ions, indicating the potential utility of 2,5-diarylthiophene derivatives in future biological studies.Graphical abstract

Enhancing D/A Interactions via Porphyrin Isomerization to Improve Photovoltaic Performance.

The interactions between the electron donors and electron acceptors (D/A) play important roles for the performance of organic solar cells (OSCs).While the isomerization strategy is known to optimize molecular geometries and properties, the impacts of isomerization on the donors or acceptors in D/A interactions have not been extensively investigated.Here in, we innovatively investigated the impacts of donor isomerism on the D/A interactions by synthesizing two small molecule donors m-ph-ZnP2and p-ph-ZnP2by linking two functionalized porphyrins at the meta and para positions of phenyl groups, respectively.Compared with p-ph-ZnP2, m-ph-ZnP2displays reduced self-aggregation but with PC61BM.Consequently, a much higher power conversion efficiency (PCE) of 5.43% is achieved for the m-ph-ZnP2binary OSCs than the p-ph-ZnP2devices with a PCE of 2.03%.The enhanced performance of m-ph-ZnP2-based device can be primarily attributed to the stronger intramolecular charge transfer (ICT), the enhanced D/A interactions, the improved charge transfer, and the suppressed charge recombination.Furthermore, the ternary devices based on m-ph-ZnP2:Y6:PC61BM achieve a PCE of 8.34%. In short, this work elucidates the relationship among the chemical structure, D/A interactions and device performance, providing valuable guidelines for designing efficient OSCs materials.

Effect of substituent position on assembly of compounds bearing ortho/para over meta directing groups

This research investigated the impact of substituent location on intermolecular interactions and crystal packing. A class of N-(dichlorophenyl)-2-pyrazincarboxamide derivatives were synthesized and characterized: 2,5-dichloro (2,5-diCl), 3,4-dichloro (3,4-diCl), and 2,4-dichloro (2,4-diCl). Comparison with their monochloro counterparts (2-chloro (2-Cl), 3-chloro (3-Cl), and 4-chloro (4-Cl)) revealed a distinct structural variation upon introducing a second chlorine substituent at the ortho/para positions of the phenyl ring. Conversely, incorporating a second chlorine atom at the meta position resulted in similar molecular packing. These findings suggest that ortho/para directing groups play a dominant role in dictating the crystal assemblies of the studied compounds.

Design, Synthesis, and Evaluation of New Pyrazolines As Small Molecule Inhibitors of Acetylcholinesterase.

In pursuit of identifying small molecule inhibitors of acetylcholinesterase (AChE), the synthesis of new 2-pyrazolines was performed efficiently. A modified spectrophotometric method was used to examine their inhibitory effects on AChE as well as butyrylcholinesterase. Four compounds (2a, 2g, 2j, and 2l) were identified as selective AChE inhibitors. Molecular docking studies were conducted to explore their potential interactions with the active site of AChE (PDB code: 4EY7). 1-(3-Nitrophenyl)-3-(thiophen-3-yl)-5-[4-(4-morpholinyl)phenyl]-2-pyrazoline (2l) exerted significant AChE inhibitory action with an IC50 value of 0.040 μM close to donepezil (IC50 = 0.021 μM). In addition to π-π interactions with Tyr341, Tyr124, and Trp86 residues, compound 2l was also capable of forming two hydrogen bonds and a salt bridge at the active site of AChE thanks to its nitro group at the meta position of the phenyl moiety linked to the N 1 position of the pyrazoline scaffold. The higher inhibitory effect of compound 2l on AChE when compared to other compounds in this series might be explained by these additional interactions. Based on the in vitro parallel artificial membrane permeability assay, compound 2l was found to have high blood-brain barrier permeability. In vitro and in silico studies suggest that compound 2l is a potent inhibitor of AChE, which is an important target for neurodegenerative disorders, particularly Alzheimer's disease.

Candidaantarctica Lipase B mediated kinetic resolution: A sustainable method for chiral synthesis of antiproliferative β-lactams

Biocatalysis is a valuable industrial approach in active pharmaceutical ingredient (API) manufacturing for asymmetric induction and synthesis of chiral APIs. Herein, we investigated synthesis of a panel of microtubule-destabilising antiproliferative β-lactam enantiomers employing a commercially available immobilised Candida antarctica lipase B enzyme together with methanol and MTBE. The β-lactam ring remained intact during chiral kinetic resolution reactions, plausibly due to a bulky N-1 phenyl substituent on the β-lactam ring substrate. The predominant reaction mediated by CAL-B was methanol catalysed conversion of the β-lactam 3-acetoxy substituent to a 3-hydroxyl group, with preferential methanolysis of the 3S, 4S enantiomer. The unreacted substrate underwent progressive enantioenrichment to the 3R, 4R enantiomer. Substitution patterns on the B ring C3 meta position of the β-lactam scaffold greatly affected the rate of reaction. Halo substituents (fluoro-, chloro- and bromo-) reduced the rate of conversion compared to unsubstituted analogues, which in turn increased enantiomeric excess (ee). Ee values up to 86 % for the 3S, 4S 3-hydroxyl enantiomer were achieved. A double resolution approach for unreacted substrate yielded high ee values (>99 %) for the 3R, 4R 3-acetoxy enantiomer. CAL-B mediated methanolysis is a more sustainable method for resolution of racemic antiproliferative β-lactams compared to a previous technique of chiral diastereomeric resolution. Yields of β-lactams obtained using CAL-B are far superior than previously described, which will facilitate progression toward pre-clinical and clinical development. Biocatalysis is a useful tool in the toolbox of the medicinal chemist.

QSAR of acyl alizarin red biocompound derivatives of &lt;i&gt;Rubia tinctorum&lt;/i&gt; roots and its ADMET properties as anti-breast cancer candidates against MMP-9 protein receptor: &lt;i&gt;In Silico&lt;/i&gt; study

Alizarin is a polycyclic compound isolated from roots of Rubia tinctorum that has potential as a breast anticancer candidate. Increasing anticancer activity can be done through structural modification to produce derivatives in the form of group substitution in the meta position using acyl. The purpose of this work is to forecast the anticancer activity of alizarin and its derivatives on the MMP-9 receptor using. Important biological activity factors will be identified by Quantitative Structure Activity molecular docking Relationship (QSAR) and projected absorption, distribution, metabolism, elimination, and toxicity (ADMET). Using Molegro Virtual Docker (MVD), molecular docking was carried out on the MMP 9 receptor (4WZV.pdb). LogP, Etot, and MR are the physicochemical parameters that are examined in order to produce QSAR. Statistical Package for the Social Science (SPSS) was used for the QSAR analysis. The pkCSM was utilized to determine ADMET prediction. The acyl alizarin derivatives have a lower rerank score than alizarin, according to the docking results so that they are predicted to have more potent anticancer activity. The QSAR analysis's findings indicated that logP and Etot had the greatest effects on the alizarin compound's and its derivatives' activity. The results of the ADMET prediction indicate that acyl alizarin is less harmful and superior to alizarin. Research findings show that it is possible to synthesize acyl alizarin derivatives, especially alizarin octanoate, which will then be tested in vitro or in vivo to determine its anti-breast cancer activity and toxicity.

Engineering the Substrate Specificity of (S)-β-Phenylalanine Adenylation Enzyme HitB.

Adenylation enzymes catalyze the selective incorporation of aminoacyl building blocks in the biosynthesis of nonribosomal peptides and related natural products. Although β-amino acid units are one of the important aminoacyl building blocks in natural product biosynthesis, very little is known about the engineering of β-amino acid adenylation enzymes. In this study, we engineered the substrate specificity of the (S)-β-phenylalanine adenylation enzyme, HitB, involved in the biosynthesis of macrolactam polyketide hitachimycin. Based on the previously determined structure of HitB wild-type, we mutated Phe328 and Ser293, which are located near the meta and ortho position of the (S)-β-phenylalanine moiety, respectively. As a result, the HitB F328V and F328L mutants efficiently activated meta-substituted (S)-β-phenylalanine analogs, and the HitB T293G and T293S mutants efficiently activated ortho-substituted (S)-β-phenylalanine analogs. Structural analysis of the HitB F328L and T293G mutants with the corresponding nonhydrolyzable intermediate analogs revealed an enlarged substrate binding pocket for (S)-β-phenylalanine analogs, providing detailed insights into the structural basis for creating enzyme substrate promiscuity. Our findings may be useful for production of various β-amino acid-containing natural product analogs.

Microscopic growth of pyridinium oxime based amphipathic on graphite: Effect of relative position of substituents

AbstractAmphipathic molecules with surfactant like properties have several applications ranging from healthcare to the chemical industry. Their ability to form thin films on surfaces with ordered and controllable patterns determines their applicability. Here, we report two pyridinium oxime‐based surfactants, which possess similar aggregation properties in solution, but exhibit substantially different assembly on highly oriented pyrolytic graphite (HOPG) surface. The two compounds are regioisomers with the oxime unit placed either in meta or para position of the pyridinium ring. While the para isomer assembled to anisotropic one‐dimensional (1D) islands and long rod‐like structures, the meta isomer formed two‐dimensional (2D) islands on the HOPG surface. This difference is rationalized through molecular level force‐field calculations that show anisotropy in the growth of the para isomer resulting from an effective overlap of the alkyl chains and oxime groups, which is distinctly not feasible in the assembly of the meta isomer. The assembly of these compounds is compared with another oxime‐containing compound of similar structure, but without the charged pyridinium unit. The charged unit seems to be crucial for the preferential formation of multilayer islands even at low coverage.

Red‐Shifting ESIPT Fluorescence by Site‐Specific Functionalization in 2‐(2’‐hydroxyphenyl)benzazole Derivatives

AbstractWe describe the synthesis, full photophysical study, and ab initio calculations of 2‐(2’‐hydroxyphenyl)benzazole (HBX) fluorophores substituted, at the meta position of the phenol group, by pyridine derivatives. HBX are commonly used as model dyes to study the stimuli‐induced modulation of the Excited State Intramolecular Proton Transfer (ESIPT) process. The meta‐substituted fluorophores reported herein, display a photophysical profile different from the previously reported ortho‐ and para‐substituted HBO pyridine isomers. Indeed, while all dyes undergo spontaneous deprotonation in neutral conditions, leading to highly emissive anionic species; upon protonation, ortho‐ and para‐pyridine substitution leads to resonance‐stabilized keto isomers, formed after ESIPT. Protonated meta derivatives, unable to stabilize their excited structure by such electronic delocalization process, display sizable intramolecular charge transfer (ICT) processes, translating into significantly redshifted emission. In addition, all dyes present a strong emission intensity, not only in neutral and acidic solutions, but also in the solid‐state. The nature of the emissive transitions was confirmed in each case by theoretical calculations combining Time‐Dependent Density Functional Theory (TD‐DFT) and second‐order Coupled Cluster (CC2) methods.