Zhaodi Liu

Crystal structures, photophysical properties and significantly different two-photon excited fluorescence of the trans- and cis-oligo(phenylene vinylene)

The crystal structures and two-photon absorbing properties of trans-/cis-oligo(phenylene vinylene) derivatives were reported for the first time. Both experimental and theoretical results revealed that the two-photon absorption cross sections of them largely depend on their conformations.

Solvent-dependent “turn-on” fluorescence chemosensor for Mg2+ based on combination of CN isomerization and inhibition of ESIPT mechanisms

A fluorescent chemosensor (L) for Mg(2+) has been synthesized and characterized, which exhibits turn-on fluorescence response for Mg(2+) only in alcohol solvent (methanol or ethanol) with high sensitivity and selectivity. But in both nonpolar and polar solvents (cyclohexane, DCM, DMSO or MeCN), L showed negligible fluorescent response for Mg(2+). In order to discover the unique phenomenon, optical measurements, liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and a high performance liquid chromatography with a fluorescence detector (HPLC-FLD) of L and L with Mg(2+) ions in solvents were studied. In alcohol solvent, [L+alcohol molecule] was formed and the mechanism aspect of L concerning the remarkable fluorescence response for Mg(2+) has been discussed.

A highly selective colorimetric and fluorescent chemosensor for Al(III) based-on simple naphthol in aqueous solution.

A colorimetric and fluorescent chemosensor (L) for Al(III) was synthesized and fully characterized. L could be both used as a colorimetric and fluorescent chemosensor for the detection of Al(3+) ions with low detection limit (8.87×10(-7) M) in CH3CN-H2O (1:1, v/v) solution. The binding ratio of L-Al(3+) was determined from the Job plot (absorption and fluorescence spectra) and MALDI-TOF MS data to be 1:1. The binding constant (Ka) of Al(3+) binding to L was calculated to be 4.8×10(5) M(-1) from a Benesi-Hildebrand plot. Moreover, the binding site of L with Al(3+) was determined by (1)H NMR titration experiment.

Four new two-photon polymerization initiators with varying donor and conjugated bridge: synthesis and two-photon activity.

A specific series of dumbbell-shaped bis-carbazoles or bis-phenothiazines dyes (1, 2, 3 and 4) constructed with styrene or biphenylethyne as the π-bridge have been synthesized and characterized. Detailed spectral properties including linear absorption, one and two-photon fluorescence properties were investigated. The results show that extending conjugated chain and introducing donors have substantial effect on their photophysical properties. Among them, two-photon absorption cross sections (σ) of the four dyes in DMF determined by the Z-scan technique are successively increased from 1 to 4 with enhancing electron-donating ability and extending conjugated chain, but electron-donating ability has larger contribution to the σ values than extending conjugated chain based on the comparison of small molecules (D-π-D). Two-photon initiation polymerization (TPIP) microfabrication experiments have been carried out using compound 4 as an initiator under irradiation of 200 fs, 76 MHz femtosecond laser at 760 nm. The results confirm that the four dyes can be effectively used as organic two-photon photopolymerization initiators.

A-π-D-π-A pyridinium salts: synthesis, crystal structures, two-photon absorption properties and application to biological imaging

Three different pyridinium salts with I−, BPh4− or [Eu(TTA)4]− anions were synthesized and fully characterized. The crystal structures and 1H-NMR spectra of the dipyridinium cations showed that the coplanarity of the cation was controlled by the type of anion. Their one- and two-photon absorption properties were studied in combination with their structure. The two-photon absorption properties were shown to be tunable by the counter-anions. A pyridinium salt containing L[Eu(TTA)4]2 was selected as a marker for use in fluorescence microscopy to image living cells. This salt clearly displayed the cell structure and was used successfully in two-photon excited fluorescence microscopy.

Two polymorphs and cocrystal of styryl-pyridine derivatives with tuned emission induced by Co2+ and Zn(phen)32+

A styryl-pyridine derivative, 2,5-dibutoxy-1,4-bis[2-(4-pyridyl)ethenyl]benzene (L), has been designed and synthesised. Two polymorphs of L and crystals of [Zn(phen)3]2L(ClO4)4 were obtained by different crystallisation conditions. Polymorph-α was prepared by a solvent evaporation method. However, polymorph-β and a cocrystal of [Zn(phen)3]2L(ClO4)4 were obtained by different inducing reagents. It has been found that there are, in total, four independent conformations of the molecule L in the three kinds of crystals. We have calculated the standard molar enthalpy of formation (ΔHm) of each conformation and demonstrated that the stabilisation energy of each conformation significantly relies on both the planarity of the molecules (L) and bond length of conjugated bridges. Furthermore, the photophysical properties of the three kinds of crystals also exhibit differences in the vibration and absorption spectroscopies, solid-state photoluminescence and time-resolved fluorescence, which may arise from the chromophores stacking modes and the intermolecular electronic interactions in the crystals. These results revealed that the optical properties of functional organic materials could be tuned by controlling their crystallisation environment for a specific molecule.

Mechanism, kinetics, and antimicrobial activities of 2-hydroxy-1-naphthaldehyde semicarbazone as a new Jack bean urease inhibitor

A new inhibitor of jack bean urease, 2-hydroxy-1-naphthaldehyde semicarbazone (HNDSC), was synthesized and its inhibitory mechanism and kinetics with respect to jack bean urease were investigated. HNDSC inhibited the activity of jack bean urease, with the inhibitor concentration leading to 50% activity loss (IC50) of 0.032 ± 0.004 mM. Kinetic analyses showed that HNDSC is a reversible and competitive inhibitor of jack bean urease. Microscopic rate constants were obtained by the progress-of-substrate-reaction method. The results obtained from inhibitory kinetic and fluorescence titration assay methods showed very good agreement that one molecule of HNDSC binds the active unit of the jack bean urease. The inhibition mechanism and kinetic studies indicate that HNDSC could be a candidate for the development of new urease inhibitors. Its antibacterial activities, evaluated against Escherichia coli, Bacillus subtilis, and Staphyloccocus aureus, were highest against E. coli.

Synthesis, crystal structures, one/two-photon optical properties and bioimaging application of two organic molecules with D–A and D–π–A models containing 6-phenyl-2,2′-bipyridine

Two novel organic compounds with D–A (L1) and D–π–A (L2) models containing 4-(N,N-dipropylamino)phenyl [donor group (D)] and 6-phenyl-2,2′-bipyridine [acceptor (A)] groups were synthesized and characterized by IR, 1H NMR, 13C NMR, MS and single crystal X-ray diffraction. Their photophysical properties were systematically investigated using both experiments and theoretic calculations. It was found that the two-photon action cross-section (δΦ) of the D–π–A model molecule (δΦL2 = 119 GM) was approximately three times larger than that of the D–A type molecule (δΦL1 = 43 GM). Furthermore, their cytotoxicity and applications in bioimaging were determined. The results showed that L1 and L2 could be used as cytoplasmic dyes with high stability and low cytotoxicity.