Jieying Wu

Aggregation-Induced Fluorescence Behavior of Triphenylamine-Based Schiff Bases: The Combined Effect of Multiple Forces

Eight triphenylamine (TPA)-based Schiff bases that exhibit different aggregation-induced emission (AIE) or aggregation-caused quenching (ACQ) behavior in tetrahydrofuran (THF)/water mixtures have been synthesized and characterized. The photophysical properties in solution, aqueous suspension, film, and the crystalline state along with their relationships were comparatively investigated. The single-crystal structures of 1-8 indicate that compact π···π stacking or excimers induce fluorescence quenching of 1, 2, 5, and 7. However, the existence of J aggregates or multiple intra- and intermolecular interactions restrict the intramolecular vibration and rotation, enabling compounds 3, 4, 6, and 8 to exhibit good AIE character. The size and growth process of particles with different water fractions were studied using scanning electron microscopy, which demonstrated that smaller uniformly dispersed nanoparticles in the THF/water mixtures favor fluorescence emission. The above results suggest that the combined effects of multiple forces caused by structural variation have a great influence on their molecular packing, electronic structure, and aggregation-induced fluorescence properties. In addition, piezofluorochromic experiments verified the potential applications of 4 and 6.

Facile synthesis and systematic investigations of a series of novel bent-shaped two-photon absorption chromophores based on pyrimidine.

The synthesis, structure, and single- and two-photon spectroscopic properties of a series of pyrimidine-based (bent-shaped) molecules are reported. All these stable heterocyclic compounds are fully characterized, and exhibit intense single- and two-photon excited fluorescence (SPEF and TPEF) over a wide spectral range from blue to red, with the spectral peak position of the SPEF being basically the same as that of the TPEF. The well-conjugated pi-systems, observed from the crystal structure, indicate the charge transfer feature of the ground state. Meanwhile, the theoretical and experimental studies indicate that the charge transfer from donor to acceptor is greatly enhanced in the excited states and the different substituted donor groups on the pyrimidine have a large effect on the optical and electrochemical properties. Based on typical structure data and comprehensive spectral data, the following structure-property relationships can be determined: for such bent-shaped chromophores, the absorption and the fluorescence wavelength maximum of the SPEF and TPEF, and two-photon absorption cross sections show a similar trend with increasing electron-donating strength of the corresponding terminal group and the number of branches, while the average bond lengths of the pi-linkage and HOMO-LUMO energy levels show an inverse trend. Experimental data and theoretical calculation provide a coherent picture. With these findings, bent-shaped quadrupolar chromophores combining peak TPA cross sections (up to 2280 GM), broad TPA bands throughout the whole 700-900 nm range, and high fluorescence quantum yields could, thus, be obtained. Such compounds are of particular interest for TPEF microscopy, as well as optical data storage in the visible and NIR regions. A data recording experiment proved the potential application of these materials.

Substituent group variations directing the molecular packing, electronic structure, and aggregation-induced emission property of isophorone derivatives.

A series of new isophorone derivatives (1-5), incorporating the heterocyclic ring or aza-crown-ether group, with large Stokes shifts (>140 nm), have been synthesized and characterized. 1-4 display aggregation-induced emission behaviors, while dye 5 is highly emissive in solution but quenched in the solid state. It was found that the tuning of emission color of the isophorone-based compounds in the solid state could be conveniently accomplished by changing the terminal substituent group. The photophysical properties in solution, aqueous suspension, and crystalline state, along with their relationships, are comparatively investigated. Crystallographic data of 1-4 indicate that the existence of multiple intermolecular hydrogen bonding interactions between the adjacent molecules restricts the intramolecular vibration and rotation and enables compounds 1-4 to emit intensely in the solid state. The size and growth processes of particles with different water fractions were studied using a scanning electron microscope, indicating that smaller globular nanoparticles in aqueous suspension are in favor of fluorescence emissions. The above results suggest that substituent groups have a great influence on their molecular packing, electronic structure, and aggregation-induced emission properties. In addition, fluorescence cell imaging experiment proved the potential application of 5.

Investigations and facile synthesis of a series of novel multi-functional two-photon absorption materials

Six centrosymmetric D–(π–A)3 structural triphenylamine derivatives that can be used as two-photon photopolymerization and optical data storage chromophores, tris[4-(4-pyridylethenyl)phenyl]amine (1), tris[4-(2-pyridylethenyl)phenyl]amine (2), tris(4-cyanoethenylphenyl)amine (3), tris[4-butylacrylatephenyl]amine (4), tris[4-methylacrylatephenyl]amine (5) and tris[4-acrylicethenylphenyl]amine (6), have been successfully synthesized via a triple palladium-catalyzed Heck coupling reaction, and the novel chromophores were fully characterized by elemental analysis, IR, 1H-NMR and ESIMS. The structure for 3 was determined by single crystal X-ray diffraction study. One- and two-photon absorption and fluorescence in various solvents were experimentally investigated. Two-photon initiated polymerization microfabrication and optical data recording experiments were carried out under 780 nm laser radiation, and the possible polymerization mechanism is discussed based on theoretical calculations. All the six chromophores have relatively large two-photon absorption cross-sections, and exhibit optical memory and highly efficient two-photon initiated polymerization abilities.

Four new two-photon absorbing imidazo[4,5-f]1,10-phenanthroline dye derivatives with different dipole moment orientation based on different groups: synthesis, optical characterization and bioimaging

A new series of D–π–A type two-photon absorption (2PA) dyes (1–4) based on imidazo[4,5-f]1,10-phenanthroline have been synthesized and their photophysical properties have been systematically investigated. These dyes showed obvious positive solvatochromic effects mainly due to intramolecular charge transfer (ICT). The two-photon absorption (2PA) cross-section values measured by two-photon excited fluorescence (TPEF) were determined to be 1232 GM and 4752 GM for dye 3 and dye 4, while dyes 1 and 2 do not display 2PA activity. These results demonstrate that their 2PA cross section values (σ) increase with increasing donor/acceptor (D/A) strength of the corresponding molecule. The results also imply that the replacement of the tetrazol group with the aza-crown-ether group results in an opposite charge transfer direction, which has been verified by density functional theory (DFT) calculations. In addition, a two-photon fluorescence cell imaging experiment proved the suitability of dye 3 for this potential application .

Difunctional chemosensor for Cu(II) and Zn(II) based on Schiff base modified anthryl derivative with aggregation-induced emission enhancement and piezochromic characteristics

Three new anthryl Schiff base derivatives containing a similar molecular structure were synthesized through a simple method and their fluorescent properties were investigated in detail. Among these, compound 1 displayed an aggregation-induced emission (AIE) feature, 2 exhibited an aggregation-induced emission enhancement (AIEE) property, while 3 showed aggregation-caused quenching (ACQ) behavior. Single-crystal structure and theoretical calculation analysis show that the larger conjugation and the existence of multiple intra- and intermolecular interactions restricts the intramolecular vibration and rotation, which benefit the emission in the condensed state, while the tight dimer structure and intramolecular torsional motion induce fluorescence quenching. Moreover, compound 2 can be utilized as fluorescence on–off type sensor for Cu2+ in methanol–H2O (4/1, v/v, pH 7.2) HEPES buffer solution, as well as fluorescence off–on type sensor for Zn2+ in pure methanol solution. The 2 : 1 ligand-to-metal coordination pattern of the 2-Cu2+ and 2-Zn2+ were calculated through a Jobs plot, and were further confirmed by X-ray crystal structures of complexes 2-CuBr2 and 2-ZnCl2. In addition, 2 also exhibits a piezofluorochromic characteristic.

Schiff base particles with aggregation-induced enhanced emission: random aggregation preventing π–π stacking

Three Schiff bases containing phenylbenzoxazole were synthesized and characterized, which exhibited distinct aggregation-induced enhanced emission (AIEE) behavior in THF–water. However, the single-crystals of L3 show obvious π–π stacking that would induce fluorescent quenching in the solid state. In order to further gain insight into the AIEE mechanism of the three compounds, the size and growth process of particles with different water fractions were studied using SEM, TEM and DLS. The results show that the molecules of compounds can slowly assemble in an ordered fashion to form more-crystalline but less-emissive particles in the THF–water mixtures with low water contents, while in mixtures containing very large amounts of water, the molecules of compounds abruptly agglomerate to form less-crystalline or even amorphous but more-emissive clusters, which effectively avoid π–π stacking.

Synthesis, Crystal Structures, Photophysical Properties, and Bioimaging of Living Cells of Bis-β-Diketonate Phenothiazine Ligands and Its Cyclic Dinuclear Complexes

Two bis-β-diketones, RCOCH(2)CO-EPTZ-COCH(2)COR (EPTZ = 10-ethylphenothiazine; R = C(6)H(5) for H(2)L(1) and CF(3) for H(2)L(2)) and their cyclic dinuclear Zn(II), Cd(II), Ni(II), Mn(II), Cu(II), Co(II) complexes have been synthesized and fully characterized. Their crystal structures were determined by single crystal X-ray diffraction analysis. Their photophysical properties have been further investigated both experimentally and theoretically. The results revealed that significant enhancement of two-photon absorption cross section values were obtained for the cyclic dinuclear Zn(II) and Cd(II) complexes compared with their free ligands. Additionally, confocal microscopy and two-photon microscopy fluorescent imaging of MCF-7 cells labeled with two ligands and Zn(II) complexes reveal their potential applications as a biological fluorescent probe.

A series of triphenylamine-based two-photon absorbing materials with AIE property for biological imaging

A specific series of D-π-A (1A-3A) and D-π-A (1B-3B) structural chromophores with various electron donors and π-conjugated bridges were designed, synthesized, and fully characterized. Their crystal structures were determined by single crystal X-ray diffraction analysis. The one/two-photon absorption properties of the chromophores have been successfully tuned by using different electron donors and π-bridges. Interestingly, it was found that chromophore 3B shows quite weak fluorescence in pure DMSO, while a significant AIE (aggregation-induced emission) effect is observed in water-DMSO (v/v 90%) mixtures with a sharp increase in fluorescence intensity of about 11 times. Furthermore, chromophore 3B shows strong two-photon excited fluorescence (TPEF) and has a large 2PA action cross-section (394 GM). The results of live-cell imaging experiments show that 3B can be effectively used as a bio-imaging probe in two-photon fluorescence microscopy towards HepG2 cells in vitro. The TPEF images of 3B not only exhibit cellular cytosol uptake but also exhibit actin regulatory protein uptake which are different from OPEF images.

Schiff base derivatives containing heterocycles with aggregation-induced emission and recognition ability

Three new Schiff base derivatives possessing vagarious blue aggregation-induced emission (AIE) characteristics in tetrahydrofuran (THF)–water were synthesized. Their photophysical properties in solution, aqueous suspension, film and crystalline states, along with their relationships, were comparatively investigated. The crystallographic data for dye 1 and dye 3 indicated that the existence of multiple intermolecular hydrogen bonding interactions restricted intramolecular vibration and rotation. Moreover, the sizes and growth processes of particles with different water fractions were studied using a scanning electron microscope (SEM) and dynamic light scattering (DLS). The results showed that the small homogeneous particles, assembled in an ordered fashion with appropriate water contents, exhibited distinct AIE behavior. Moreover, in a THF–H2O (4 : 1, v/v) solution of HEPES (20 mM) buffer, dye 2 showed fluorescence turn-on sensing towards Cr3+ and Al3+via chelation enhanced fluorescence (CHEF). The 2 : 1 stoichiometries of the sensor complexes (dye 2–Cr3+ and dye 2–Al3+) were calculated from Job plots based on fluorescence titrations.