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Exploring the organic molecular structural features and supramolecular interactions provide basis for developing stimuli-responsive organic solid-state fluorescent materials. Herein, we have synthesized methoxyphenyl-substituted carbazole-based π-conjugated derivatives (Cz-MN, Cz-ECA, Cz-CA, Cz-CAA and Cz-NBA) with different acceptor units and investigated their influence on solid-state fluorescence. All five compounds showed aggregation-induced emission (AIE) in the solid state with acceptor-dependent tunable fluorescence from 488 to 602 nm (quantum yield (Φf) = 7.2 to 1.9%). Cz-ECA exhibited blue-shifted fluorescence, whereas Cz-NBA showed red-shifted fluorescence. Cz-MN, Cz-ECA and Cz-CA revealed relatively strong solid-state fluorescence compared to Cz-CAA and Cz-NBA. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) calculations suggested intramolecular charge transfer (ICT) from the carbazole donor to the acceptor unit. Mechanofluorochromic studies of Cz-MN and Cz-ECA showed self-reversible fluorescence switching but the other three AIEgens did not show any stimuli–response. Single crystal structural analysis of Cz-MN, Cz-ECA and Cz-CA showed twisted molecular conformations with different intermolecular interactions. Both Cz-MN and Cz-ECA did not show any strong intermolecular interactions in the crystal lattice. In contrast, Cz-CA exhibited strong amide–amide complementary H-bonding and an extended network structure. Hence, the twisted molecular conformation and the absence of strong intermolecular interactions in Cz-MN and Cz-ECA contributed to self-reversible mechanofluorochromism (MFC). Thus, the present study is expected to provide further insight to design AIEgens with stimuli-responsive self-reversible fluorescent materials. [ABSTRACT FROM AUTHOR]

Developing organic fluorescent molecules with multi-functional properties such as stimuli responses, fluorescence tuning, sensing, white light emission and bioimaging is highly desirable because of their application potential. Herein, we synthesized a triphenylamine (TPA)-based red-emitting ionic fluorophore, (E)-4-(4-(diphenylamino)styryl)-1-alkylpyridin-1-ium (TPA-P), with varied alkyl chain lengths (TPA-P-1 (methyl), TPA-P-7 (heptyl) and TPA-P-14 (tetradecyl)) and utilized them for fluorescence tuning, white light emission, chlorinated solvent sensing and latent fingerprinting applications. TPA-P ionic fluorophores showed anion-dependent tunable solid-state fluorescence from 564 to 671 nm. Single crystal structural studies suggested the anion exchange and modulation of molecular packing in the solid state. Further, TPA-P-1 revealed distinctly different colors and fluorescences towards sodium dodecyl sulphate (SDS) anions in an aqueous medium. Limit of detection (LOD) analysis indicated a sensing response up to 0.8 μM of SDS. TPA-P fluorophores also exhibited sensitive color changes in chlorinated solvents. TPA-P exhibited distinguishable fluorescence in ortho-dichlorobenzene (o-DCB) and meta-dichlorobenzene (m-DCB) isomers. The ionic nature of red-emitting fluorophores was exploited to generate a stable white light-emitting solution by mixing with blue fluorescent polystyrene sulphonate (PSS). CIE chromaticity indicated 0.32, 0.33 color coordinates, which are very close to pure white light emission. The red fluorescence and lipophilic alkyl chain of the TPA-P-14 ionic fluorophore were utilized for latent fingerprinting via powder dusting, which showed well-defined finger marks up to level 3 information. Thus, the quaternization of pyridine nitrogen in TPA π-conjugated fluorophores red shifted the fluorescence, and ionic functionality was further utilized to tailor functional fluorescence properties. [ABSTRACT FROM AUTHOR]

A series of triphenylamine‐quinoxaline donor‐acceptor (bipolar) compounds (TPA‐QH, TPA‐QMe, TPA‐QCOOH and TPA‐QNO2) with different substituents were synthesized and investigated their fluorescence properties, including stimuli‐induced fluorescence responses in solution and the solid‐state. Single crystal structural analysis revealed non‐planar molecular conformation, substituent controlled intermolecular interactions and molecular packing in the crystal lattice. TPA‐QH, TPA‐QMe, TPA‐QCOOH and TPA‐QNO2 showed tunable solid‐state emission from green to red. TPA‐QH showed strong fluorescence at 487 nm (quantum yield (Φf)=28.3 %) whereas NO2 substituted TPA‐QNO2 exhibited relatively weak fluorescence at 610 nm (Φf=4.3 %). Density functional theoretical (DFT) calculations also indicated reduction of optical bandgap with substituting electron withdrawing group. The donor‐acceptor structure with intramolecular charge transfer (ICT) resulted solvent polarity dependent fluorescence tuning. The presence of acid responsive quinoxaline group was utilized to demonstrate pH‐responsive fluorescence switching and dual state fluorescence was utilized for fabricating rewritable fluorescent platform. Thus, the present study provides a structural insight to develop dual state emissive triphenylamine–quinoxaline based bipolar materials for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Triphenylamine (TPA)‐based Schiff base chemosensors ((E)‐2‐((4‐(diphenylamino)benzylidene)amino)phenol [TPA‐AP], (E)‐5‐(diphenylamino)‐2‐(((2‐hydroxyphenyl)imino)methyl)phenol [HTPA‐AP], and (E)‐5‐(diphenylamino)‐2‐((phenylimino)methyl)phenol [HTPA‐A]) were synthesized and explored the role of metal chelating hydroxyl functionality position for heavy metal ion sensing. TPA‐AP and HTPA‐AP showed Cu2+ ion‐induced chemical transformation and produced oxazole derivatives with turn‐on fluorescence. In contrast, HTPA‐A exhibited metal chelation‐induced turn‐on fluorescence for Zn2+ ion. The reactive chemical sensing of TPA‐AP and HTPA‐AP led to high selectivity of Cu2+, and other ions did not show any interference. The concentration‐dependent studies of Cu2+ and Zn2+ indicated the limit of detection (LOD) up to 6.07 × 10−7 and 4.6 × 10−7 M, respectively. Further, Cr3+, Fe3+, and Fe2+ coordination with TPA‐AP and HTPA‐AP exhibited visible color change from colorless to yellow. However, the yellow color was disappeared and becomes colorless due to imine hydrolysis. Interestingly, all three metal ions showed different rate of hydrolysis and color disappearance. TPA‐AP with Fe3+ exhibited fast hydrolysis and immediate color change whereas Fe2+ and Cr3+ required longer time. But HTPA‐AP and HTPA‐A produced stable complexes with Cr3+, Fe2+, and Sn2+ and Fe3+ alone showed hydrolysis. Thus, the present studies provide structural insight for designing reactive fluorescence and colorimetric Schiff base chemosensor for heavy metal ions. [ABSTRACT FROM AUTHOR]

This document discusses the prediction of crystal systems or space groups using machine learning based on databases. It highlights the development of algorithms for predicting space groups from chemical composition, with a focus on their application in powder X-ray diffraction analysis. The document also explores the statistics of space groups for inorganic and organic crystals, as well as the differences in databases for inorganic compounds, organic compounds, and protein crystallography. It concludes by discussing the influence of molecular and supramolecular symmetry on the symmetry of supramolecular aggregations and the potential for future developments in theories and data utilization methods. [Extracted from the article]

Metal–organic frameworks are a good platform for investigating the correlation of structures with physical properties due to the facile coordination environment changes and their responsive structures to external stimuli such as pressure, temperature, and gas sorption. In this study, we report a proton conductivity switching behavior in Zn5FDC, [Zn5(μ3-OH)2(FDC)4(solvent)2] (FDC = 9H-fluorene-2,7-dicarboxylate) triggered by relative humidity (RH). Interestingly, depending on the presence and absence of coordinating molecules the MOFs show distinctively different tendencies in their proton conductivity. Two isostructural Zn5FDC compounds, [Zn5(μ3-OH)2(DEF)2(FDC)4] (Zn5FDC-DEF) and [Zn5(μ3-OH)2(FDC)4] (Zn5FDC-OMS; OMS = open metal site), are prepared, in which the three-dimensional connectivities are identical, but the local structures in the secondary building units (SBUs) are different. In the measurement of humidity-dependent conductivity, both MOFs show a dramatic proton conductivity switching phenomenon (ON/OFF ratio, approximately 108), but the conductivity switching occurs at different RHs for each MOF (above RH 70% in Zn5FDC-DEF, and above RH 90% in Zn5FDC-OMS at 298 K). During this process water coordination in metal centers leads to their structural transformation into Zn5FDC-H2O, which means that the different coordination structures by the absence/presence of coordination solvents provide different water access environments to metal centers. The computational calculation supports that the structural transformation of Zn5FDC-OMS triggered by moisture exposure occurred under higher relative humidity conditions than simple coordination solvent replacement in Zn5FDC-DEF. This study proves that the coordination solvents play a role in conductivity variation, and it provides a new design strategy for functional solid-state proton conductors. [ABSTRACT FROM AUTHOR]

The coordination environment and networks of metal–organic frameworks (MOFs) play a significant role in their functional properties, especially catalysis. In recent years, the use of MOFs for electrocatalytic water-splitting reactions to produce green hydrogen fuel has gained increasing attention. Herein, we report the preparation of Co-benzene dicarboxylic acid-based MOFs (Co-MOF-1 and Co-MOF-2) with different coordination environments and correlated their structure-controlled electrocatalytic OER activity in an alkaline medium. Both Co-MOF-1 and Co-MOF-2 showed 3D network structures with different coordination environments around the Co metal centre. In Co-MOF-1, the Co metal centre is coordinated with DMF and pyridine along with a benzene dicarboxylic acid (BDC) ligand, whereas the Co metal centre is coordinated only with BDC ligands in Co-MOF-2. The Co metal centres in Co-MOF-1 contain labile solvent coordination but have completely saturated coordination with the BDC ligand alone in Co-MOF-2. Interestingly, Co-MOF-1 showed relatively strong OER activity and required the overpotential (η) of 294 mV to produce 10 mA cm−2 current density. However, Co-MOF-2 required the overpotential of 343 mV to achieve the 10 mA cm−2 current density. Further Co-MOF-1 showed comparatively low Tafel slope and charge transfer resistance and high electrochemical surface area than Co-MOF-2 and supported the enhanced OER activity. XPS analysis of Co-MOF-1 before and after catalysis suggested the conversion of Co-MOF-1 to CoOOH during the electrocatalysis that boosted the OER activity. The presence of a labile coordination site in Co-MOF-1 might have facilitated the interaction of hydroxyl electrolyte with the metal centre and active site generation by forming CoOOH easily which enhanced the OER activity. Co-MOF-1 also showed excellent stability for over 48 h. Hence, the present work provides structural insight for designing new MOFs for electrocatalytic water-splitting reactions. [ABSTRACT FROM AUTHOR]

The condensation reaction between naphthylacetonitrile isomers and anthracene aldehyde produced unexpected highly twisted AIEgens (2-(naphthalen-1-yl)-2-(10-oxo-9,10-dihydroanthracen-9-yl)acetonitrile (1) and (Z)-3-(anthracen-9-yl)-2-(naphthalen-2-yl)acrylonitrile (2)). 1 and 2 exhibited strong solid-state fluorescence and mechanical stimuli-induced reversible fluorescence switching. Crystallization of 2 in acidic CHCl3–CH3OH produced Cl substituted anthracene (2-Cl), whereas in CH2Cl2 pure crystals of 2 were produced. Single crystal analysis of 1 revealed a twisted conformation in the middle ring of anthracene due to carbonyl introduction. The carbonyl oxygen and cyano nitrogen are involved in the H-bonding interactions in the crystal lattice. 2 showed slipped stacking between naphthyl units whereas 2-Cl exhibited intermolecular H-bonding between Cl and anthracene hydrogens. 1 exhibited strong solid-state fluorescence (λmax = 541 nm, quantum yield (Φf) = 18.2%), whereas 2 and 2-Cl displayed tunable and relatively low fluorescence efficiency (λmax = 547 (2), 489 nm (2-Cl), Φf = 6.3 (2) and 3.6% (2-Cl)). Computational studies suggested clear intramolecular charge transfer (ICT) in 1 compared to 2 and 2-Cl. Further, 1 and 2-Cl showed mechanical crushing and heating induced reversible fluorescence switching but 2 did not show any fluorescence switching. Powder X-ray diffraction indicated a reversible phase transformation upon crushing and heating that caused reversible fluorescence switching. Hence, the present study provides insight into the subtle structural impact on intermolecular interactions and solid-state fluorescence. [ABSTRACT FROM AUTHOR]