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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]

• The Schiff base senses Al(III) ions with a fluorescent enhancement. • The detection mechanism involves formation of an octahedral Al(III) complex. • Sensing mechanism was delineated using spectral and DFT/TD-DFT studies. • The probe detected Al(III) successfully in different natural matrices. Spectroscopic investigation and Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) calculations have been carried out to delineate the mechanism of fluorescent detection of Al(III) by a new Schiff base (CN3) in an aqueous solution. CN3 was synthesized and characterized using 1H and 13C NMR and mass spectral techniques. Upon adding Al(III), the weak fluorescence of CN3 (512 nm) became enhanced with a slight blue shift to 502 nm. CN3 served as an efficient probe for highly selective and sensitive Al(III) detection without the interference of environmentally and biologically significant cations and anions. The limit of detection (LOD) was determined to be 1.3 µM. Job's continuous variation method of analysis suggested the formation of a 1:1 complex between CN3 and Al(III), which was confirmed as an octahedral complex by 27Al NMR and mass spectral data. The binding constant of the complex was found to be 7×104 M−1. The mode of coordination of CN3 with Al(III) was ascertained by 1H NMR titration experiments. CN3 served as an OONN-type tetradentate ligand to form a chelate, which is responsible for the enhancement of fluorescence of CN3 upon binding with Al(III) due to chelation enhanced fluorescence (CHEF) mechanism. The optical properties of CN3 and its Al(III) complex were corroborated well by DFT and TD-DFT calculations. [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]