A Colorimetric and Fluorimetric Chemodosimeter for Copper Ion Based on the Conversion of Dihydropyrazine to Pyrazine

Copper-mediated oxidation of imidazopyrazinones inhibits marine luciferase activity

The development of bioluminescence-based tools has seen steady growth in the field of chemical biology over the past few decades ranging in uses from reporter genes to assay development and targeted imaging. More recently, coelenterazine-utilizing luciferases such as Gaussia, Renilla, and the engineered nano-luciferases have been utilized due to their intense luminescence relative to firefly luciferin/luciferase. The emerging importance of these systems warrants investigations into the components that affect their light production. Previous work has reported that one marine luciferase, Gaussia, is potently inhibited by copper salt. The mechanism for inhibition was not elucidated but was hypothesized to occur via binding to the enzyme. In this study, we provide the first report of a group of nonhomologous marine luciferases also exhibiting marked decreases in light emission in the presence of copper (II). We investigate the mechanism of action behind this inhibition and demonstrate that the observed copper inhibition does not stem from a luciferase interaction but rather the chemical oxidation of imidazopyrazinone luciferins generating inert, dehydrated luciferins.

Modular Two-Step Access to π-Extended Naphthyridine Systems-Potent Building Blocks for Organic Electronics

Efficient synthetic approaches for the incorporation of nitrogen into polyaromatic compounds (PACs) in different patterns as stabilising moiety for π-extended systems and modification tool for optoelectronic properties remain a challenge until today. Herein, we developed a new versatile pathway to napthyridine-based PACs as non-symmetric and regioisomeric pendant to pyrazine-based PACs. A combination of a gold-catalysed synthesis of 2-aminoquinolines and the development of an in situ desulfonation and condensation of these precursors are the key steps of the protocol. The shape and type of attached functional groups of the PACs can be designed in a late stage of the overall synthetic procedure by the chosen anthranile and backbone of the ynamide introduced in the gold-catalysed step. Single-crystal X-ray diffraction and the investigation of electronic properties of the compounds show the influence of the attached substituents. All naphthyridine-based PACs show halochromic behaviour implying their use as highly sensitive proton sensor in non-protic solvents.

Triphenylamine/Tetracyanobutadiene-Based π-Conjugated Push-Pull Molecules End-Capped with Arene Platforms: Synthesis, Photophysics, and Photovoltaic Response

π-Conjugated push-pull molecules based on triphenylamine and 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) have been functionalized with different terminal arene units. In solution, these highly TCBD-twisted systems showed a strong internal charge transfer band in the visible spectrum and no detectable photoluminescence (PL). Photophysical and theoretical investigations revealed very short singlet excited state deactivation time of ≈10 ps resulting from significant conformational changes of the TCBD-arene moiety upon photoexcitation, opening a pathway for non-radiative decay. The PL was recovered in vacuum-processed films or when the molecules were dispersed in a PMMA matrix leading to a significant increase of the excited state deactivation time. As shown by cyclic voltammetry, these molecules can act as electron donors compared to C₆₀ . Hence, vacuum-processed planar heterojunction organic solar cells were fabricated leading to a maximum power conversion efficiency of ca. 1.9 % which decreases with the increase of the arene size.

Highly Selective Fluorimetric Turn-Off Detection of Copper(II) by Two Different Mechanisms in Calix[4]arene-Based Chemosensors and Chemodosimeters

Isoxazolo-pyrene tethered calix[4]arenes selectively detect copper(II) ions without interference from related perchlorate ions. The fluorescence emission of the probes, synthesised by nitrile oxide alkyne cycloaddition, and characterised by spectroscopic and crystallographic data, is rapidly reduced by Cu(II) ions. Detection limits are in the micromolar or sub-micromolar range (0.3-3.6 μM) based on a 1 : 1 sensor:analyte interaction. Voltammetric behaviour and ¹ H NMR data provide new insights into the sensing mechanism which is dependent on the calixarene substitution pattern. When the calixarene lower rim is fully substituted, Cu(II) detection occurs through a traditional chelation mechanism. In contrast, for calixarenes 1,3-disubstituted on the lower rim, detection takes place through a chemodosimetric redox reaction. The isolation of a calix[4]diquinone from the reaction with excess Cu(ClO₄ )₂ provides confirmation that the sensor-analyte interaction culminates in irreversible sensor oxidation.

Diaminomaleonitrile-based Fluorophores as Highly Selective Sensing Platform for Cu2

A colorimetric and turn-on fluorescent chemodosimeter 1 based on diaminomaleonitrile was synthesized for Cu²⁺ detection. It showed high selectivity and sensitivity towards Cu²⁺ over the other tested metal ions. Probe 1 in acetonitrile exhibited a strong absorption band at 530 nm and weak fluorescence emission when excited at 480 nm, while the addition of Cu²⁺ could lead to a 30-nm blue shift of the absorption band and a remarkable fluorescence enhancement. Moreover, the detection limit of probe 1 for Cu²⁺ was calculated to be 28 nM. Quite different from the reported mechanism based on a metal-complexation induced fluorescence enhancement, the sensing mechanism was proved to be based on the Cu²⁺-promoted hydrolysis reaction, which was confirmed by ¹H NMR, ¹³C NMR and mass spectrum analysis. Studies on probe 2 were carried out to verify the universality of this sensing mechanism.

Acid Responsive Hydrogen-Bonded Organic Frameworks

A porous hydrogen-bonded organic framework (HOF) responsive to acid was constructed from a hexaazatrinaphthylene derivative with carboxyphenyl groups (CPHATN). Precise structures of both 1,2,4-trichlorobenzene solvate [CPHATN-1(TCB)] and activated HOF with permanent porosity (CPHATN-1a) were successfully determined by single-crystalline X-ray diffraction analysis. Permanent porosity of CPHATN-1a was evaluated by gas sorption experiments at low temperature. CPHATN-1a also shows significant thermal stability up to 633 K. Its crystals exhibit a rich photochemistry thanks to intramolecular charge-transfer and interunit proton-transfer reactions. Femtosecond (fs) experiments on crystals demonstrate that these events occur in ≤200 fs and 1.2 ps, respectively. Moreover, single-crystal fluorescence microscopy reveals a shift of the emission spectra most probably as a result of defects and a high anisotropic behavior, reflecting an ordered crystalline structure with a preferential orientation of the molecular dipole moments. Remarkably, CPHATN-1a, as a result of the protonation of pyradyl nitrogen atoms embedded in its π-conjugated core, shows reversible vapor acid-induced color changes from yellow to reddish-brown, which can be also followed by an ON/OFF of its emission. To the best of our knowledge, this is the first HOF that exhibits acid-responsive color changes. The present work provides new findings for developing stimuli responsive HOFs.

Pyridine-ring containing twisttetraazaacene: Synthesis, physical properties, crystal structure and picric acid sensing

Novel pyridine-ring containing twisttetraazaacene 9,14-diphenylpyreno[4,5-g]isoquinoline (1) and its full-carbon derivative 9,14-diphenyldibenzo[de,qr]tetracene (2) have been synthesized and fully characterized. Studies showed that compound 1 could identify picric acid (PA) over other common nitro compounds with high selectivity and sensitivity. Upon the addition of PA, the emission peak of compound 1 in CH₃CN was red shifted from 447 to 555nm with a fluorescence quenching efficiency as high as 95%, the detection limit was calculated to be 2.42μM, while its full-carbon derivative (2) could not exhibit this kind of performance. The possible mechanism with the enhanced PA detection efficiency in pyridine-ring containing twisttetraazaacene (1) than its full-carbon derivative (2) was also investigated.

Fluorescent phenanthroimidazoles functionalized with heterocyclic spacers: synthesis, optical chemosensory ability and two-photon absorption (TPA) properties

Fluorescent phenanthroimidazoles bearing heterocyclic spacers as novel optical chemosensors and two-photon absorption chromophores.

Fusing N-heteroacene analogues into one "kinked" molecule with slipped two-dimensional ladder-like packing

An unexpected "kinked" N-heteroacene with a slipped two-dimensional ladder-like packing feature is produced from the conventional condensation reaction. The as-obtained compound [2,2']bi(5,12-bis(TIPS)piperazin-3-one[2,3-b]phenazine) (2BPP) consists of two identical backbones (5,12-bis(TIPS)piperazin-3-one[2,3-b]phenazine), which are fused together through a C[double bond, length as m-dash]C double bond and two intramolecular H-bonds. A study on the charge carrier transport indicates that a 2BPP single crystal has a hole mobility up to 0.3 cm2 V-1 s-1, while theoretical calculations suggest that this compound might possess potential well-balanced ambipolar charge-transport characteristics.

A paper-based biomimetic device for the reduction of Cu(ii) to Cu(i) – application to the sensing of Cu(ii)

An unprecedented heterogeneous biomimetic device for the reduction of Cu(ii) to Cu(i) through the covalent immobilization of thioglycolic acid onto cellulose paper was developed. The device was used as a very efficient colorimetric and optical detection system for the Cu(ii) species.

A π-extended luminogen with colorimetric and off/on fluorescent multi-channel detection for Cu2+ with extremely high selectivity and sensitivity via nonarylamine-based organic mixed valence

A luminogen (ITP-TPE) comprising isothianaphthene-bridged tetraphenylethene units was efficiently synthesized.

Azaacenes as active elements for sensing and bio applications

Recent progress in the application of azaacenes in sensing and bio-fields has been summarized.