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• Synthesis of AIEgens with unsymmetrical intramolecular H-bonding functionalities. • Large Stoke shifted emission in the solid-state by ESIPT process. • Molecular structure dependent self-assembly, fluorescence efficiency and tunable emission. • Highly reversible mechanofluorochromism. We have synthesized two new ESIPT fluorophores (1-((E)-((E)-((2-hydroxyphenyl)(phenyl)methylene)hydrazono)methyl) naphthalen-2-ol (Naph-2-OH) and 5-(diphenylamino)-2-((E)-((E)-((2-hydroxyphenyl)(phenyl) methylene)hydrazono)methyl) phenol (TPA-2-OH)) with two unsymmetrical intramolecular H-bonding functionalities and investigated the solid-state structural assembly and fluorescence properties. The crystal structure analysis confirmed the formation of strong intramolecular H-bonding and twisted molecular conformation. The nonplanar twisted molecular conformation produced well separated molecules in the crystal lattice that lead to strongly enhanced emission ((λ max = 538 nm, Φ f = 5.2% (Naph-2-OH), λ max = 562 nm, Φ f = 13.4% (TPA-2-OH)). Density functional theoretical (DFT) calculation supported the fluorescence tuning and intramolecular charge transfer (ICT) from TPA donor to imine acceptor. Both Naph-2-OH and TPA-2-OH showed mechanical crushing and heating induced reversible fluorescence switching due to the reversible phase transformation between crystalline and amorphous state. ESIPT fluorophores with two unsymmetrical intramolecular H-bonding exhibited structure dependent molecular packing, solid state fluorescence and mechanofluorochromism. [Display omitted] [ABSTRACT FROM AUTHOR]

• Synthesis growth and molecular interaction of organic nonlinear optical single crystals of (E)-N′-(2,3-dimethoxybenzylidene)−4-fluorobenzohydrazide (DMB-FBH) were discussed. • X-ray single-crystal diffraction analysis confirmed the structure. • Vibrational analysis and various electronic properties of the compound were studied using density functional theory (DFT) calculations. • Hirshfeld surface analyses and fingerprint plots confirmed the O...H, N...H, C...C and C...H intermolecular hydrogen bonds interaction. • UV–visible and the fluorescence emission spectra of the DMB-FBH in aqueous solutions were recorded. • Third order nonlinear optical susceptibility (χ3) of DMB-FBH was determined by Z-scan measurement. Organic nonlinear optical single crystals of (E)-N′-(2,3-dimethoxybenzylidene)-4-fluorobenzohydrazide (DMB-FBH) were synthesized and grown using slow evaporation crystallization from ethanol solution. The single crystal X-ray diffraction scattering revealed that the DMB-FBH crystallised in the tetragonal crystal system with a centro symmetric space group of I 4 1 /a. The crystallographic bond lengths and bond angles were compared with the values generated from optimized molecular geometry based on quantum chemical calculations. The functional group vibrations were identified theoretically by density functional theory with B3LYP 6–311 G (d,p) basis set using Gaussian 09 software package and their vibrations were compared with the experimental FT-IR spectra. The UV-visible and the fluorescence emission spectra of the DMB-FBH in aqueous solutions were recorded. The HOMO-LUMO energy level pictogram addressed the intramolecular charge transfer (ICT) interaction between donor and acceptor moieties and their impact on the energy gap was determined. Different interactions such as O···H, N···H, C···C and C···H in DMB-FBH were quantified via fingerprint plots and these results were compared with that of similar structure. The detailed molecular docking simulation was carried out with M. tuberculosis protein [PDB ID:2 × 22]. The third order nonlinear optical susceptibility (χ3) of DMB-FBH was confirmed experimentally by Z-scan method and their conversion efficiency was higher than the other hydrazones derivatives. In short, this work discusses the crystal structure, identification and quantification of the molecular interactions, thermal, antimycobacterial and optical properties of new hydrazone derivative. Energy frameworks (left) coloumb dispersion (center) and total energy (right) of DMB-FBH crystal structure. [Display omitted] [ABSTRACT FROM AUTHOR]

A new highly selective fluorescent turn-on probe (RS4) possessing indolinium moiety has been designed and synthesized for the detection of cyanide ion. The probe RS4 displays instantaneous, highly selective and sensitive recognition of cyanide ion over other common anions via change in color and enhancement in fluorescence. Nucleophilic addition of cyanide to the indolinium C-atom leads to the enhancement in fluorescence (λ em 481 nm; Blueish-green emission) and decolourization due to different intramolecular charge transfer (ICT) process. The binding constant of the 1:2 RS4 /CN¯ adduct is determined to be 2.3 × 104 M−1. The limit of detection of cyanide by RS4 is estimated to be 21 nM. Density functional theory (DFT) based calculations strongly substantiate the results of the experimental investigations. Importantly, the probe detects cyanide ion in agro-products (cassava powder and bitter almond), which demonstrates its value to practical application. • The probe senses cyanide with color change and fluorescent enhancement. • The detection mechanism involves nucleophilic addition of CN− at indolinium C-atom. • Sensing mechanism was delineated using spectral and DFT studies. • The probe successfully sensed CN− of cyanogenic glycoside in agro-products. [Display omitted] [ABSTRACT FROM AUTHOR]

Herein, two new thiazole derivatives: ethyl2-(2-benzylidenehydrazinyl)thiazole-4-carboxylate (3) and ethyl2-(2-(2-hydroxybenzylidene)hydrazinyl)thiazole-4-carboxylate (4) were synthesized by cyclization of 1-benzylidenethiosemicarbazide with ethyl bromopyruvate. The synthesis was validated by spectroscopic techniques like FTIR, 1H- NMR, 13C-NMR and chemical structure of title compounds 3 and 4 has been determined using SC-XRD. Ancillary to experimental analysis, DFT calculations with B3LYP/6-311 + G (d,p) level were performed for comparative analysis of FT-IR spectroscopic data, optimized geometry, frontier molecular orbitals (FMOs), natural bond orbital (NBO) analysis and nonlinear optical (NLO) properties. Overall, experimental findings were supported by corresponding DFT computed results. TDDFT calculations were executed at M06/6-311 + G (d,p) level of theory to calculate the vertical electronic transition states. NBO analysis disclosed that intramolecular charge transfer and hyper-conjugative interactions among bonds provide stability to the investigated compounds 3 and 4. The global reactivity parameters calculated from energy of FMOs indicates that 3 and 4 enclose larger softness and fewer hardness values. NLO results of 3 and 4 were observed better than standard molecule recommended the NLO activity of said compounds. We hope that this joint experimental and computational insight may provide new ways for the utilization of title molecules as NLO material for optoelectronic applications. Image 1 • Two novel ethyl 2-(2-(2-substitutedbenzylidene)hydrazinyl)thiazole-4-carboxylate crystals were synthesized. • XRD, 1H NMR, 13C NMR, FT-IR and UV–Vis were performed for the characterization. • Computational study was done at B3LYP/6-311 + G (d,p) level for comparative analysis. • Comparative study reveals a good agreement between experimental and DFT results. • FMOs, NBO analysis and nonlinear optical (NLO) properties were calculated. [ABSTRACT FROM AUTHOR]