Ni(II), Cu(II), and Zn(II) Cryptate-Enhanced Fluorescence of a Trianthrylcryptand: A Potential Molecular Photonic OR Operator

A Fluorescence Sensor for Cu2+ and Co2+ Based on Click-Generated Triazole Moiety

Abstract. The novel tetraphenylethylene (TPE) based sensor 1 bearing bis(2-pyridin-2-ylmethyl) amine (BPA) unit and BODIPY unit linked with triazole moieties could be obtained by click reaction efficiently. It was employed as a fluorescence probe for the selective recognition of Cu2+and Co2+. They form stable 1:1 stoichiometric complexes and the lowest limit of detection was 1×10-7 M.

A near-infrared fluorescent probe for detecting copper(II) with high selectivity and sensitivity and its biological imaging applications

The first near-infrared fluorescent probe was developed toward Cu(2+). Based on the photo-induced electron transfer (PET) mechanism, the probe exhibited weak fluorescence. Upon the addition of Cu(2+), it fluoresced strongly. The probe offered this unique capability, and was successfully applied to living cells, tissues and in vivo to visualize Cu(2+).

Photochemical "triode" molecular signal transducer

A molecular "hexad" in which five bis(phenylethynyl)anthracene (BPEA) fluorophores and a dithienylethene photochrome are organized by a central hexaphenylbenzene unit has been prepared. Singlet-singlet energy transfer among the BPEA units occurs on the 0.4 and 60 ps time scales, and when the dithienylethene is in the open form, the BPEA units fluoresce in the 515 nm region with a quantum yield near unity. When the dithienylethene is photoisomerized by UV light to the closed form, which absorbs in the 500-700 nm region, the closed isomer strongly quenches all of the excited singlet states of BPEA via energy transfer, causing the fluorescence quantum yield to drop to near zero. This photochemical behavior permits the hexad to function in a manner analogous to a triode vacuum tube or transistor. When a solution of the hexad is irradiated with steady-state light at 350 nm and with red light (>610 nm) of modulated intensity, the BPEA fluorescence excited by the 350 nm light is modulated accordingly. The fluorescence corresponds to the output of a triode tube or transistor and the modulated red light to the grid signal of the tube or gate voltage of the transistor. Frequency modulation, amplitude modulation, and phase modulation are all observed. The unusual ability to modulate intense, shorter-wavelength fluorescence with longer-wavelength light could be useful for the detection of fluorescence from probe molecules without interference from other emitters in biomolecular or nanotechnological applications.

Transition metal ions or acid-induced suppression of photoinduced proton transfer and electron transfer reaction in 5-(4-fluorophenyl)-2-hydroxypyridine: a molecule of dual mode fluorosensitivity

The photophysical properties of 5-(4-fluorophenyl)-2-hydroxypyridine (FP2HP) at different pH and its fluorescence response toward different transition metal ions have been studied by steady-state absorption and emission spectroscopy in combination with quantum chemical calculations. Although keto-enol tautomerization is observed in the excited state, the molecule is weakly fluorescent due to the presence of electron-rich nitrogen atom and relatively electron-deficient fluorine atom, which may lead to photoinduced electron transfer process. In the presence of the transition metal ions, such as Zn(2+) , Cd(2+) , Hg(2+) , etc., the studied molecule exhibits changes in its absorption and emission properties. The present system shows fluorescence enhancement instead of usual quenching in presence of the transition metal ions, such as Fe(2+) and Cu(2+) . Spectral observation leads to the interpretation that this structurally simple molecule can be effectively utilized as a chelation-enhanced fluorescence-based chemosensor for the detection of transition metal ions. The experimental findings corroborate well with theoretical calculations at Hartree-Fock level using 6-31G** and lanl2dz basis sets.

A colorimetric and fluorescent turn-on chemosensor operative in aqueous media for Zn2+ based on a multifunctionalized spirobenzopyran derivative

By conjugating spiropyran chloride 8 with 2-amino-N-(quinolin-8-yl)acetamide (5), multifunctionalized spirobenzopyran derivative SPQN was designed and synthesized as a water soluble colorimetric and fluorescent turn-on chemosensor for Zn(2+). In 50% aqueous ethanol buffer solution, SPQN displayed a selective chelation fluorescence enhancement (16-fold) at 650 nm and visible color change (from colorless to red) with Zn(2+) among the metal ions examined. In addition, as the third channel to display the metal binding characteristics of SPQN, operating on an efficient FRET process between the quinoline and the merocyanine moiety of the sensor, ratiometric determination of Zn(2+) can be realized.

A new highly selective, ratiometric and colorimetric fluorescence sensor for Cu(2+) with a remarkable red shift in absorption and emission spectra based on internal charge transfer

A new 1,8-diaminonaphthalene based ratiometric and highly selective colorimetric "off-on" type of fluorescent probe, receptor 2 has been designed and synthesized that senses only Cu(2+) among the other heavy and transition metal ions examined on the basis of internal charge transfer (ICT). The visual sensitivity of the receptor 2 is remarkable, showing dual color changes from colorless (receptor) to purple followed by blue and a large red shift in emission upon Cu(2+) complexation.

Nickel(II) and iron(III) selective off-on-type fluorescence probes based on perylene tetracarboxylic diimide

Two novel "turn-on" fluorescent probes with perylene tetracarboxylic diimide (PDI) as the fluorophore and two different di-(2-picolyl)-amine (DPA) groups as the metal ion receptor (PDI-1 and PDI-2) were successfully synthesized with satisfactory yields. PDI-1 exhibited high selectivity toward Ni(2+) in the presence of various other metal cations including Zn(2+), Cd(2+) and Cu(2+) which were expected to interfere significantly. A 1 : 2 stoichiometry was found for the complex formed by PDI-1 and Ni(2+) by a Job's plot and by non-linear least square fitting of the fluorescence titration curves. By introducing an extra diamino ethylene group between DPA and the phenyl bridge, the receptor was modified and the high selectivity of the sensor toward Ni(2+) shifted to Fe(3+). The enhancement factor of the fluorescence response of PDI-2 to Fe(3+) was as high as 138. The binding behavior of the receptors in these two compounds is affected significantly by the PDI fluorophores. Most interestingly, both Ni(2+) and Fe(3+) are paramagnetic metal ions, which are known as fluorescence quenchers and are rarely targeted with "turn-on" fluorescence probes. This result suggests that PDIs are favorable fluorophores for a "turn-on" fluorescence probe for paramagnetic transition metal ions because of their high oxidation potential.

A Unimolecular Half-Subtractor Based on Effective Photoinduced Electron Transfer and Intramolecular Charge Transfer Processes of 1,8-Naphthalimide Derivative

We report a unimolecular system as a combinatorial logic half-subtractor based on a naphthalimide derivative. Chemical inputs (OH– and H+) can significantly change the absorption and fluorescence characteristics through modulating intramolecular charge transfer and photoinduced electron transfer process upon protonation or deprotonation of the molecule. An XOR gate is obtained following the absorbance variations at 485 nm, and an INHIBIT gate is induced when the output signal is monitored at 535 nm in the fluorescence spectra. Large differences in output signals allow unequivocal assignment of logic-0 and logic-1 of both logic gates, which may function in parallel to implement the half-subtractor.

Metal-chelating and dansyl-labeled poly(N-isopropylacrylamide) microgels as fluorescent Cu2+ sensors with thermo-enhanced detection sensitivity

We report on the fabrication of Cu2+-sensing thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgels labeled with metal-chelating acceptor and fluorescent reporter moieties. Cu2+ detection sensitivity can be considerably enhanced via thermo-induced collapse of the sensing matrix, which can easily optimize the relative spatial distribution of Cu2+-binding sites and fluorescence readout functionalities. A novel picolinamine-containing monomer with Cu2+-binding capability, N-(2-(2-oxo-2-(pyridine 2-yl-methylamino)ethylamino)ethyl)acrylamide (PyAM, 3), was synthesized at first. Nearly monodisperse Cu2+-sensing microgels were prepared via emulsion polymerization of N-isopropylacrylamide (NIPAM) in the presence of a nonionic surfactant, N,N'-Methylene-bis(acrylamide) (BIS), PyAM (3), and fluorescent dansylaminoethyl- acrylamide (DAEAM, 5) monomers at around neutral pH and 70 degrees C. At 20 degrees C, as-synthesized microgels in their swollen state can selectively bind Cu2+ over other metal ions (Hg2+, Mg2+, Zn2+, Pb2+, Ag+, and Al3+), leading to prominent quenching of fluorescence emission intensity. Above the volume phase transition temperature, P(NIPAM-co-PyAM-co-DAEAM) microgels exhibit increased fluorescence intensity. It was observed that Cu2+ detection sensitivity can be dramatically enhanced via thermo-induced microgel collapse at elevated temperatures. At a microgel concentration of 3.0x10(-6) g/mL, the detection limit drastically improved from approximately 46 nM at 20 degrees C to approximately 8 nM at 45 degrees C. The underlying mechanism for this novel type of sensor with thermotunable detection sensitivity was tentatively proposed.