Xiaoping Gan

Rationally designed two-photon absorption compounds based on benzoxazole derivatives: structure–property relationships and bio-imaging applications

A new series of benzoxazole-based two-photon absorption (2PA) chromophores (T1-5) were synthesized and fully characterized. Among them, T1-3 are linear donor (D)-π-acceptor (A) type fluorophores with various electron-donating groups, while T4 and T5 are multi-branched compounds stemming from T3. Their photophysical properties have been systematically investigated, and the two-photon absorption properties indicate that the highest 2PA cross-section (σ2PA) is 2702 GM for T5 (in DMF). Structure-property relationships of the chromophores are comprehensively discussed based on their optical properties, crystal structures and density functional theory (DFT) calculations. In addition, a two-photon fluorescence cell imaging experiment demonstrates the potential bio-application of T1-5 with good photostability and low cytotoxicity.

Various unique coordination patterns of Hg and DFT calculations to determine the formation of a 3-D supramoleculer framework by covalent and noncovalent interactions.

By combining a large pi-conjugated bidentate ligand L: 3,6-dipyrazole-N-ethylcarbazole with HgI(2), an extraordinary supramolecular coordination polymer, [Hg(4)L(2)I(8)](infinity), has been prepared. The crystal structures of the ligand and its coordination polymer were determined by X-ray crystallography, which shows three varied coordination modes especially the rare asymmetric quadruply bridged trinuclear moieties in [Hg(4)L(2)I(8)](infinity). Density functional theory (DFT) calculations (ADF) performed on model dimers show the roles of covalent and noncovalent interactions in establishing the three-dimensional architecture.

Branched triphenylamine-core compounds: aggregation induced two-photon absorption

Three branched molecules (T1–T3) were synthesized through simple step to realize or enhance two-photon absorption (2PA) in aggregates. Spectra data show that one- and two-branched molecules (T1 and T2) possessed remarkable AIE properties, which came from the formation of J-aggregation because of their partial planarization in an aggregated state. SEM and DLS illustrate that the ordered aggregation and the small particle size had an important influence on fluorescence emission. Open aperture Z-scan experiments show that T1 and T2 possessed excellent 2PA properties in the aggregated state. The largest 2PA cross section was 8314 GM for T2 in aggregates, which was about 13-fold higher than that in pure solution. All the results demonstrate that the compounds could obtain outstanding 2PA performance by rationally adjusting their structure or changing state, which could provide a reference for preparing strong 2PA compounds.

A conveniently prepared and hypersensitized small molecular fluorescent probe: Rapidly detecting free zinc ion in HepG2 cells and Arabidopsis.

In this paper, we reported a conveniently prepared fluorescent probe for zinc ions detection, which constructed by the condensation reaction between p-(benzothiazolyl)aniline with 4, 4- diethylaminesalicylaldehyde. The sensing ability of the probe toward zinc ions in vitro was tested by a series of UV-Vis and fluorescence spectroscopy studies, which showed that the probe possessed high sensitivity with a detection limit of 5.8nM and a rapid response time of 10s. We also carried out fluorescent bio-imaging of the probe for zinc ions in human liver hepatocellular carcinoma cells (HepG2), which showed that the probe could be utilized to detect the intracellular endogenous zinc ions visually without introducing external zinc sources. Meanwhile, co-staining experiment with organelle selective trackers was performed to illustrate that the probe could locate at endoplasmic reticulum. Finally, we successfully used it as a zinc ion developer in plant tissue, which clearly demonstrated the distribution of zinc ions in the growth stage of plant tissue.

Intermolecular interactions boost aggregation induced emission in carbazole Schiff base derivatives

Six D-π-A model compounds (compounds 1-6) were conveniently synthesized and characterized by 1H NMR, 13C NMR, MS and single crystal X-ray diffraction. One photon absorption and emission properties were studied by using a series of UV-visible and fluorescence spectra and theoretical calculations were applied to investigate the structure-property relationships, which showed that all six compounds possessed an obvious intramolecular charge transfer process which could be attributed to their optical properties. We simultaneously investigated their fluorescence emission performance in water/acetonitrile mixtures and found that they all have outstanding aggregation induced emission properties. Scanning electron microscopy testing illustrated that orderly aggregation was the main reason for their aggregation induced emission properties. Cytotoxicity tests indicated that all these compounds had good biocompatibility for living cells, and bio-imaging studies highlighted the potential application of the six compounds in one-photon fluorescence microscopy imaging domains.

High fluorescence of carbazole derivatives for bioimaging of endoplasmic reticulum and lysosome: the influence of molecular structure on optical properties and cell uptake

Three new carbazole derivatives (L1–L3) with different functional groups have been synthesized and characterized. L1 and L2 are connected through methylene unit to construct L3 with enhanced molecular distortion configuration. The compounds exhibit dependent aggregation-induced enhanced emission (AIEE) properties and cellar uptake region in HepG2 cells. It is demonstrated that L1 and L2 exhibit modest AIEE properties in THF–H2O mixtures, while L3 shows superior AIEE character with 13 times enhancement. This is because of the enhanced molecular distortion configuration of L3 and the related restriction of π–π stacking interactions between adjacent L3 molecules resulted from the introduction of methylene unit. Due to the unique structure of the compounds, the superior fluorescence emission of L1–L3 in aqueous media, further imaging studies demonstrated the suitability of probes L1–L3 for the biological applications in both human liver hepatocellular carcinoma cells (HepG2) and plant tissues of Arabidopsis seedlings. The imidazole unit in L2 leads selective target to lysosome of HepG2 cells through acid–base interactions, while L1 and L3 are inclined to act with endoplasmic reticulum.

High contrast off–on fluorescence photo-switching via copper ion recognition, trans–cis isomerization and ring closure of a thiosemicarbazide Schiff base

An easily available triphenylamine–isophorone-based Schiff base was synthesized and its specifically triple-addressable molecular photo-switching behaviour via copper ion recognition, trans–cis isomerization and ring closure were investigated in detail. Firstly, compound Lo was able to real-time monitor Cu2+ in an acetonitrile solution via displaying the “turn-on” emission in the near infrared region with high selectivity, and sensitivity. Furthermore, two independently photochromic phenomena based on the distinct mechanisms were found surprisingly, one through the ring closure of the thiosemicarbazide moiety based on a Michael addition reaction in tetrahydrofuran solution and another through the trans–cis isomerization of aldimine (–CN–) in the solid state under the stimuli of UV/visible light. Finally, fluorescence imaging experiments in living cells demonstrated the potential practical applications in biological systems.

Application and recognition behaviors of TPA-cored probes with subtle structural change.

Two new triphenylamine-cored probes (L1, L2) with different receptor units have been synthesized and fully characterized by IR, NMR and MS spectra. Their photophysical properties have been investigated in detail. The recognition abilities of two probes were evaluated by a series of metal ions, which showed that L1 could recognize Cu(2+) over other metal ions. L2 could respond to Cu(2+), Hg(2+) in a short time, which interferes with a little each other. The Jobs plot and (1)H NMR titration of L1 with Cu(2+) and L2 with Cu(2+) (Hg(2+)) in CD3CN verified the coordination mode of complexes L1-Cu(2+), L2-Cu(2+) and L2-Hg(2+), respectively. The limit of detection of L2 for Cu(2+) was lower than that of L1 towards Cu(2+). The results demonstrated that the receptor units in the probes had remarkable effect on recognizing metal ions. Meanwhile, L1 and L2 showed potential application in bio-imaging after mixing with Cu(2+).