Design. Synthesis And Properties Of Fluorescent Probes Based On Benzothiazole And Terpyridine

Rescently, fluorescent probes has attracted much more attention for its significant useage in environmental protection, bio-imaging and medical treatment. However, although there are many probes towards metal ions and chemicals common for biology and environmental use, little studies on probes for trasition-metal ions and toxic neutral chemicals have been reported, and most of the which can not be used in vitro under extreme environment. In addition, many fluorescent probes will coordinate with two or more chemicals, resulting in similar fluorescence signal responses and poor selectivity, because of their complex nature and complicated working environments.This phenomenon can be observed in the probes for metal ions, especiallythose for transition-metal ions.To solve these problems, studies on fluorescence probes for transition-metal ions, neutral chemicals and strong acidic pH detection are performed in this paper. A series of fluorescent probes for environmental detection and bio-imaging with high sensitivity and selectivity are designed and synthesized and their structure-property relationship and solvent effect are studied. Job’s plot analysis are improved for "ON-OFF" probes To get insight into the sensing mechanism of fluorescent probes based on ICT effect for recognizing similar metal ions and and summarize a common rule, the effect of conjugated system and solvent molecules on the sensing properties of fluorescence probes are also discussed. In addition, the biocompatibility and membrane permeability of ZC-F series fluorescent probes have been confirmed through bio-imaging experiments.A novel fluorescence chemosensor based on intramolecular charge transfer (ICT) mechanism was designed and synthesized and its photophysical properties were characterized. By coordinating of Co2+and central2,6-dicarbonylpyridinyl function group, the chemosensor2,6-bis(4-diphenylamino-styrylcarbonyl)pyridine (PhPy) showed nearly complete fluorescence quenching towards Co2+while no fluorescence response to other competing cations, suggesting its potential usage in quantitative and real-time detection of Co2+. By improving Job’s plot analysis to make it suitable for "ON-OFF" fluorescent probes, the stoichiometry between PhPy and Co2+was determined. Furthermore, PhPy also exhibited significant solvatochromic effect depending on the polarity of solvent, indicating its potential usage as polarity probes.A new both fluorescent and colorimetric probe2-(4-((4-(benzo[d]thiazol-2-yl) phenyl)ethynyl)benzylidene)malononitrile (BP) based on reaction and ICT effect is designed and synthesized. The probe responds rapidly towards hydrazine and exhibits an apparent color changes from yellow to a colorless state, indicating that this probe can be used as a color indicator for hydrazine. Meanwhile, the probe also shows a significant enhancement on fluorescence by around120-fold after the addition of hydrazine in a broad band (410-700nm). With a detection limit as low as0.11ppb, the probe can detect hydrazine in a wide concentration range because of the blunted sensing functional group. The contrast test shows nearly no interruption from some common elements in water, suggesting the high selectivity of this probe towards hydrazine. Moreover, the theoretical calculation based on density functional theory (DFT) is also performed to get insight into the sensing mechanism and two different ICT modes are found. This hydrazine probe would be a promising candidate for the applications in environment protection, water treatment and safety inspection.A fluorescent pH sensor4-((4-(benzothiazol-2-yl)phenyl)ethynyl)aniline (BA) for strong acid environment based on ICT effect was realized to exhibit high stability, sensitivity and selectivity. The absorption and fluorescent emission spectra suggest that solvent molecules have significant influence on the fluorescent properties of BA, while minor effect on absorption can be observed, indicating strong ICT effect in this probe. This probe can be used to detect acidity within the range of0.5～2.5with high sensitivity and selectivity. Theoretical calculations are carried out to find that great changes of electronic locations before and after protonation lead to larger HOMO-LUMO energy gap and fluorescence enhancement. The design strategy may help to develop probes for targets at high concentration.By introducing terpyridine as recognizing function and water soluble coumarin as fluorophore, two new fluorescent probes (E)-3-(3-(4-([2,2’:6’,2"-terpyridin]-4’-yl)phenyl)acryloyl)-7-(diethylamino)-2H-chromen-2-one (ZC-F4) and3-((4-([2,2’:6’,2"-terpyridin]-4’-yl)phenyl)ethynyl)-7-methoxy-2H-chromen-2-one (ZC-F7) are designed and synthesized. Comparing with ZC-F7, ZC-F4has absorption and emission spectra located at longer wavelength because of its stronger electronic donor. Both these two probes exhibit good selectivity and sensitivity towards Zn2+even at10nM (0.65ppb) with significant variation of emission wavelength (more than100nm shifts). One can observe the emission colour converted from green to red. pH titration suggest good stability of ZC-F4under pH6-9for biology use. Job’s plot test suggests a1:1stoichiometry between probes and Zn2+, and the theoretical calculation based on density functional theory has been carried out to get insight into the sensing mechanism. Furthermore, the imaging of Zn2+in cells are also applied to test their feasibility in biology. These two fluorescence probes would be a promising candidate for the applications in cell-imaging, environment protection, water treatment and safety inspection.By conjugating terpyridine as receptor and fluorophore based on benzothiazole, two new fluorescent probes2-(4-((4-([2,2’,6’,2"-terpyridin]-4’-yl)phenyl)ethynyl) phenyl)benzo-[d]thiazole (ZC-F1) and2-(4-((7-((4-([2,2’:6’,2"-terpyridin]-4’-yl) phenyl)ethynyl)-9,9-bis(2-(2-ethoxyethoxy)ethyl)-9H-fluoren-2-yl)ethynyl)phenyl)-be nzo[d]thiazole (ZC-F2) with different fluorescence response towards Zn2+and Cd2+are designed and synthesized. Baring high fluorescence quantum yield, both of these probes recognize Zn2+and Cd2+with stoichiometry of1:1. Titration experiments suggest high sensitivity of these probes even at ppb level without interuption from other metal ions. To get insight into the sensing mechanism of these probes, theoretical calculations are carried out and the difference between the electronegativity of Zn2+and Cd2+is confirmed to be the root cause, which induces different emission spectra shift, leading to different emission color. Studies on two-photon absorption (TPA) suggest high TPA cross-section (8) of ZC-F2, while ZC-F2-Zn has higher8, which can be ascribed to higher electronegativity of Zn2+. In addition, cell imaging experiments of ZC-F2towards Zn2+and Cd2+certify its membrane permeability and biocompatibility, suggest its potential use in metal ions positioning in vivoSome rules for designing fluorescent probes which can be used to distinguish similar metal ions based on ICT mechanism are summarized through comparison of ZC-F1and ZC-F2. By enlarging the conjugating system, a probe with higher optical properties, longer emission wavelength for biology use can be expected, accompany with lower recognizing ability. Meanwhile, solvent polarity is found to be influential in the distinguishment. larger distinction between Zn2+and Cd2+can be observed in solvents with higher polarity. Thus, rational choice of conjugation system and solvents is of great importance.