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We prepared and characterized an array of polarity-sensitive fluorescent dyes (7 and 9a, 9b and 9c). Fluorescent dyes are based on imidazole cores, suitably functionalized with a conjugated push–pull system. The photophysical properties of the synthesized materials were elaborately investigated. These new fluorescent probes showed good fluorecence emission, higher φFl values and large Stokes shifts in different organic solvents because of their ICT nature. Furthermore, with aldehyde groups as the recognition sites, all the dyes could act as ratiometric fluorescent sensors towards methanol. The selective ratiometric fluorescence response towards methanol is due to the strong intermolecular H-bonding between the aldehyde unit and methanol. The detection limit of methanol was found to be at the ppm level. Methanol sensing was confirmed using emission spectroscopy, FTIR studies and theoretical calculations. Additionally, these dyes were used for the detection of methanol in biodiesel and in test paper strips. [ABSTRACT FROM AUTHOR]

Achieving deep blue thermally activated delayed fluorescent (TADF) materials with narrow emission still remains a challenge. Herein, two deep blue TADF emitters DCBTRZ and PPCTRZ were designed and synthesized by directly using host materials, 1,4-di(carbazol-9-yl)benzene (DCB) and 2-[4-(9H-carbazol-9-yl)phenyl]-1-phenyl-1H-phenanthro[9,10-d]imidazole (PPC) as donors, and 2,4,6-triphenyl-1,3,5-triazine (TRZ) as an acceptor. The two emitters have typical TADF properties. Both of them can emit deep blue fluorescence with a very narrow full-width at half-maximum (FWHM) of 42 nm in toluene. The photoluminescence quantum yields (PLQYs) of DCBTRZ and PPCTRZ are 39.6% and 38.2% in doped films, respectively. Devices based on DCBTRZ and PPCTRZ achieve deep blue emission (440 and 442 nm) with maximum external quantum efficiencies (EQEmax) of 6.68% and 6.55%, respectively. Meanwhile, they exhibit very high color purity. The CIEy and FWHM of devices employing DCBTRZ and PPCTRZ are 0.059/0.063 and 56/54 nm, respectively, meeting the standard of NTSC for deep-blue emitters, which indicates excellent application prospects in displays. The results suggest that this strategy for developing deep blue TADF materials with narrow emission and CIEy < 0.06 directly employing host materials as donors is feasible and effective. [ABSTRACT FROM AUTHOR]

Herein, two novel A–D–A structural imidazole derivatives, namely BMTPBZP and BMTPNKL, with orange and green fluorescence were successfully designed and synthesized, which exhibited an evident charge transfer (CT) excited state property. Compared with the triphenylamine-imidazole molecule TPA-BM with a simple D–A structure, which made the fluorescence red-shifted and quenched the response toward Fe3+, both BMTPBZP and BMTPNKL could selectively recognize Fe3+ based on the infrequent response of fluorescence enhancement and a blue shift with a relatively great sensitivity and anti-interference performance, suggesting that they have potential to be used as a novel fluorescence turn-on type Fe3+ sensor. The sensing mechanism study showed that the response of these two probe molecules toward Fe3+ could be attributed to the coordination reaction between Fe3+ and the electron-rich N atom on the imidazole ring in a 1 : 1 ratio, which caused the CT excited state of the probe molecules to generate a new and higher energy CT emission. In addition, the introduction of the A–D–A structure was demonstrated to be the key for obtaining the enhanced fluorescence and blue-shifted response of the probe molecules. [ABSTRACT FROM AUTHOR]

Novel V-shaped fluorophores with an imidazole skeleton composed of arylethynyl moieties were developed. Their HOMO–LUMO energy gaps were well controlled by the introduction of electron-withdrawing or -donating groups in the aryl moiety. Compounds with different substituents at the 4- and 5-positions were selectively synthesized exploiting the difference in reactivity between the iodo and bromo groups. All compounds synthesized displayed fluorescence not only in solution but also in the solid state. The compound with a donor–acceptor structure displayed a fluorescence maximum with a wavelength over 500 nm and a large Stokes shift of about 150 nm, due to its intramolecular charge transfer character. In the solid state, the synthesized compounds have planar structures, indicating an expansion of π-conjugation. Upon exposure of the compounds in the solid state to acid vapor, the fluorescence of the compounds with acceptor groups was quenched, and that of the others shifted to longer wavelengths. [ABSTRACT FROM AUTHOR]

By introducing a series of pyridine derivatives as organic moieties, four Keggin-based compounds were synthesized, namely [Ag(Py2Piz)2(H2PW12O40)]·2H2O (1), [Ag4(AcyPh)4(H2SiMo12O40)2]·2H2O (2), [Ag2(Py3Piz)2(H2O)2(H3SiMo12O40)2]·8H2O (3) and {Ag4(Py2TTz)4[Ag(PMo12O40)2]}·Ag(Py2TTz)·2(Py2TTz)·6H2O (4) (Py2Piz = 4,5-bis(2-pyridinyl)imidazole, Py3Piz = 2-(4-pyridyl)4,5-di(2-pyridinyl)imidazole and Py2TTz = 2,5-bis(4-pyridyl)thiazolo[5,4-d]thiazole). In compound 1 the [Ag(Py2Piz)2]+ subunits link Keggin anions through weak Ag-O interactions to form a 1D chain. In compound 2 two mono-supporting Keggin anions are fused by two [Ag(AcyPh)]+ subunits to construct a dimer. In compound 3 there is a mono-capped Keggin anion with an [Ag(Py3Piz)(H2O)]+ subunit. Compound 4 contains a Keggin-dimer linked by an Ag ion. Each dimer is further connected by four sets of [Ag(Py2TTz)]+ lines to construct a 3D framework. All these compounds can be used as nitrite electrochemical sensors. All of them show good photocatalytic activity for MB. In addition, compound 4 shows a selective response to Hg2+ ions. [ABSTRACT FROM AUTHOR]

The modified Debus–Radziszewski reaction was used to design and synthesize novel truxene derived blue-emitting materials bearing phenanthroimidazole substituents. The materials were prepared non-catalytically under ambient conditions using a triamino based derivative of truxene as a key precursor in good yields. The 5, 5′, 10, 10′, 15, and 15′ positions of the truxene were alkylated to provide solubility to the molecules, making the materials solution processable. The substituted phenanthroimidazole moieties were introduced at the 2, 7, 12 positions of truxene to synthesize the target molecules. Three new materials were prepared by varying the phenyl group attached at the C2 position of the phenanthroimidazole moiety, designated as PT1 for the phenyl, PT2 for the 4-methoxyphenyl, and PT3 for the 4-cyanophenyl substituent. From the photophysical studies, PT3 was found to have dominant charge transfer characteristics in its excited state. Also, PT3 exhibited a photoluminescence quantum yield as high as 0.83. The optimized geometries from the computational studies revealed that the molecules are highly twisted, with dihedral angles of ∼75°. The HOMO–LUMO distributions were found to be well separated showing the bipolar characteristic of the compounds. The band gap values from computational studies were found to be in agreement with experimental values. The emission spectra in the solid state gave maxima at 402 nm for PT1, 412 nm for PT2, and 450 nm for PT3. The materials were thus found to be emitting in the blue region of the visible spectrum. The TCSPC and TRPL studies were carried out to explore further the excited states of the molecules, wherein radiative pathways were found to be dominant. [ABSTRACT FROM AUTHOR]

In this study, two biological template molecules and two common short-chain imidazolium ionic liquids with amphipathy were selected to synthesize four different types of metal nanoclusters (MNCs), which were templated on a biological molecule/imidazolium ionic liquids (ILs) complex with properties enhancement. The fluorescence intensity and stability of the MNCs were improved in different degrees via this simple and fast protocol. The fluorescence intensity of AgNCs was significantly enhanced primarily due to aggregation-induced emission (AIE), and it was attributed to the shrinking size and donation of delocalized electrons for other MNCs. Different template molecule must match with appropriate ILs to form a steady complex that stabilizes the MNCs. The stability of the MNCs was improved, especially for AuNCs, because biological molecule/imidazolium ILs complex was found to be an effective barrier in protecting the MNCs from quenching interactions. Compared to conventional cationic surfactant (sodium dodecyl sulfate, SDS), these imidazolium ILs exhibited superior properties enhancement of the nanomaterials. MNCs with excellent properties could be applied in bioanalysis, especially in fluorescence imaging in vitro, because of their undisturbed and durable optical signal. [ABSTRACT FROM AUTHOR]

A simple salicylic acid selective fluorescence receptor 1 was designed by combining 1-pyrenecarboxaldehyde and 1-(3-aminopropyl)imidazole. The selective sensing of salicylic acid resulted in a significant increase in monomer emissions due to the π–π interactions between the benzene and pyrene rings. The nature of the interactions between receptor 1 and salicylic acid was investigated further by 1H NMR spectroscopy, and the energy minimised structure of the complex between receptor 1 and salicylic acid was optimised. Receptor 1 showed the highest binding constant with 5-nitrosalicylic acid (Ka = 7.18 × 104 M−1) among all the aromatic carboxylic acids tested. 5-Nitrosalicylic acid formed a complex with receptor 1 at a 1 : 1 ratio in EtOH. [ABSTRACT FROM AUTHOR]

The new class of ESIPT-capable molecules, benzo[a]imidazo[5,1,2-cd]indolizines, bearing the 2-hydroxyphenyl substituent were prepared in a straightforward manner from imidazo[1,2-a]pyridines via a tandem [8+2]cycloaddition–[2+6+2]dehydrogenation reaction. The relationship between the structure and photophysical properties was thoroughly elucidated by comparison with simple analogues i.e. 2-(2′-hydroxyphenyl)imidazo[1,2-a]pyridines. Compared with parent 2-(2′-hydroxyphenyl)imidazo[1,2-a]pyridines the new chromophores strongly absorb blue light and emit in the yellow part of the spectrum. In contrast to 2-(2′-hydroxyphenyl)imidazo[1,2-a]pyridines, emission of π-expanded dyes in protic solvents is usually weaker than in aprotic ones, where they exhibit large Stokes shifts (5500–7000 cm−1). Unlike in solution, in the solid state luminescence for benzo[a]imidazo[5,1,2-cd]indolizines is shifted on average by 100 nm relative to the fluorescence of the corresponding imidazo[1,2-a]pyridines, which results in a relatively strong (Φfl = 0.18 to 0.27) emission of the red light. Benzo[a]imidazo[5,1,2-cd]indolizines possessing a methoxy substituent have much higher fluorescence quantum yields than analogues bearing fluorine and methyl substituents. [ABSTRACT FROM AUTHOR]

A fluorescent chemosensor was designed and synthesized by incorporating the imidazolium and 1,8-naphthalimide dye moieties into a preorganized tripodal receptor. The novel sensor displays high selectivity for Cu(ClO4)2 and Cu(NO3)2 over a wide range of tested metal ions, anions, and Cu2+ salt ion pairs. Upon adding Cu(ClO4)2 or Cu(NO3)2 to the probe solution, the fluorescence emission was significantly turned on concomitant with a blue shift in the emission energy, due to an anion-induced conformational change and coordination effect. Further binding model studies by 1H nuclear magnetic resonance spectroscopy and mass spectroscopy demonstrated that the receptor formed a 1 : 1 host–guest complex with Cu(ClO4)2 or Cu(NO3)2. [ABSTRACT FROM AUTHOR]

Red shining perylene fluorescent dyes were obtained by their lateral extension with imidazole attached with methoxysilanes and applied for the grafting of silica nanoparticles. The interaction of chromophores at the surface of the nanoparticles was managed by external media and controlled their optical properties. [ABSTRACT FROM AUTHOR]