A new naphthoquinone-based chemosensor 2-((3hydroxyphenyl)amino)-3-(phenylthio)naphthalene-1,4-dione (2HPN) was successfully synthesized for the selective detection of Fe 2+ . The sensing property of the chemosensor 2HPN was evaluated in aqueous acetonitrile (CH 3 CN) medium by a fluorescence emission method. The metal-binding studies of the ligand 2HPN showed selective "turn-on" fluorescence responses for Fe 2+ (K a = 1.0 × 10 6 M −1 ). The detection limit of the ligand 2HPN to Fe 2+ was calculated to be 0.272 μM, which is lower than the World Health Organization recommendation (0.3 mg/L) in drinking water. The most significant feature of the obtained chemosensor 2HPN is its ability to sense Fe 2+ via naked-eye detection over various metal ions. The chemosensor operated via the intramolecular charge transfer effect, which was supported by Fourier transform infrared analysis, NMR titrations, and quantum chemical calculations. The efficiency of the chemosensor 2HPN as a biomarker for Fe 2+ was successfully proven by imaging in human cancer cells and zebrafish. Thus, the chemosensor 2HPN could be a useful biomarker for the precise sensing of Fe 2+ in clinical diagnosis.

Like siloles, benzosiloles have low lying LUMOs due to σ*-π* conjugation between Si and the butadiene moiety but are more amenable for structural tuning. In total, 27 benzosiloles, 12 of them already synthesized and another 15 newly reported here, have been investigated using DFT and TDDFT calculations with an aim to check their suitability for optoelectronic applications. Our results show that all these molecules have excellent π-conjugation throughout. Frontier molecular orbital analysis gives an estimate of the band gap of these benzosilole derivatives and further reveals that the LUMOs are highly localized on the benzosilole moiety whereas HOMOs are localized on both the benzosilole moiety and the substituents. TDDFT calculations have been performed to understand the absorption properties in gas and solvent phases. PCM calculations show that solvation has a minimum effect on absorption maxima. Among the different functionals, PBE0 was found to perform well compared to other functionals and the computed absorption spectra are in good agreement with experiments. Among the designed candidates, styryl substituted benzosiloles are the most promising, showing higher wavelength of absorption and would make better OLED materials. NBO and AIM analysis provide evidence for complete delocalization in these systems. It is interesting to note that eleven out of the fifteen newly designed candidates have lower band gaps than the best known benzosilole derivatives synthesized so far.

A phenoxazine-based fluorescence chemosensor 4PB [(4-(tert-butyl)-N-(4-((4-((5-oxo-5H-benzo­[a]­phenoxazin-6-yl)­amino)­phenyl)­sulfonyl)­phenyl)­benzamide)] was designed and synthesized by a simple synthetic methods. The 4PB fluorescence chemosensor selectively detects Ba2+ in the existence of other alkaline metal ions. In addition, 4PB showed high selectivity and sensitivity for Ba2+ detection. The detection limit of 4PB was 0.282 μM and the binding constant was 1.0 × 106 M–1 in CH3CN/H2O (97.5:2.5 v/v, HEPES = 1.25 mM, pH 7.3) medium. This chemosensor functioned through the intramolecular charge transfer (ICT) mechanism, which was further confirmed by DFT studies. Live cell imaging in MCF-7 cells confirmed the cell permeability of 4PB and its capability for specific detection of Ba2+ in living cells.

A simple naphthoquinone−dopamine hybrid (2CND) was designed and fabricated as a colorimetric and fluorescence chemosensor for the selective recognition of Sn 2+ in the aqueous medium. This simply accessible chemosensor was prepared by connecting of naphthoquinone acceptor and dopamine donor moieties via Michael-like addition reaction. The chemosensor 2CND showed a turn-on fluorescence response which operated through the inhibited photoinduced electron transfer effect. The sensor probe shows remarkable performance, such as high selectivity, sensitivity, excellent water solubility, and rapid response to Sn 2+ (less than 5 s). The detection mechanism of the 2CND−Sn 2+ complex was supported by FT-IR analysis, 1 H NMR titration, and DFT calculations. Besides, the 1:1 binding stoichiometry was confirmed by the ESI-MS spectral analysis. Furthermore, the chemosensor 2CND has been successfully employed as a fluorescence probe to monitor trace Sn 2+ in live cells and zebrafish. The sensor probe 2CND could serve as an effective fluorescence bioimaging probe for the discriminative detection of diseased and normal human cells.

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