Zhipeng Yu

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.

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 .

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.

Aggregation induced emission in the rotatable molecules: the essential role of molecular interaction

Aggregation-induced emission (AIE) compounds, dye2 and dye3, with a rotatable N–N single bond and aza-crown-ether, have been synthesized. The fluorescence intensities of both dyes are very weak in THF, while become extraordinarily strong in a mixture of H2O–THF (v/v 95%). They are increased by 88.9 and 70.7 times, respectively, indicating enhanced blue-green fluorescence emissions. The λem of these two compounds in different states has been well studied. Besides this, dye1 and dye2 were characterized by single crystal X-ray structural determination. The results show that molecular interactions are formed in the particles, which considerably restrict the intramolecular vibration and rotation.

Role of anions in preparing silver(I) complexes with a new multidentate ligand: polymorphs, structures and nonlinear optical properties

A new multidentate ligand containing pyridyl and pyrazolyl groups, 6-phenyl-4-(4-(1H-pyrazolyl)phenyl)-2,2′-bipyridine (L) was designed and synthesized. By self-assembly of L with silver(I) salts, three new complexes containing disilver(I) metallocycles, namely [TsOAgL]2 (1), [AgL]2(ClO4)2 (2) and [AgL2]2(NO3)2[AgLNO3]2·(H2O)2 (3), were obtained. Polymorph (II) of L was obtained unexpectedly when AgSCN complex was prepared. In complexes 1 and 2, two ligands in a head-to-tail mode bridge two Ag(I) ions via pyridyl and pyrazolyl N atoms to generate binuclear [AgL]2 unit. While, in complex 3, the asymmetric unit contains two kinds of crystallographically and conformationally independent molecules with completely different structures and coordination environments of Ag(I) ions. The structure of one kind of molecule is similar to that of complex 1. However, the other kind has a uninuclear structure, and the Ag(I) center is coordinated by four pyridyl nitrogen atoms from two ligands. Different anions have shown a great influence on both the molecular structures and the packing structures of the complexes. The nonlinear optical (NLO) properties of L and the complexes were measured through Z-scan technique. The results show that they may be good candidates for non-linear optical materials.

Photon-induced intramolecular charge transfer with the influence of D/A group and mode: optical physical properties and bio-imaging

Five triphenylamine containing benzimidazole derivatives (a1–a5) with different D/A groups (D and A stand for donor and acceptor, respectively), conjugation length or configuration were designed and synthesized. The one- and two-photon spectroscopic properties of these molecules were studied. All of these compounds have amazing fluorescence quantum yields in the range of 0.39–0.61. Besides, for a1–a5, the λem (emission maximum wavelength of one- and two-photons) are only dominated by the D/A groups, and the conjugation length is irrelevant, implying that the molecular rotation is in the excited-state. To better explain this phenomenon, the structure–property relationships of a1–a5, especially the molecular rotation in the excited-state, have been discussed in detail, and were identified by density functional theory calculations. Furthermore, four azo-heterocycle containing benzimidazole derivatives, which have weak electron-donating ability, were synthesized and discussed as a comparison. Finally, considering their optical action, cytotoxicity and solubility, a1, a2 and a4 were chosen for bio-imaging. The results show that the small molecule a2 is the best candidate for one-photon excited fluorescence and two-photon excited fluorescence imaging.

A new imidazophenanthroline derivative and its Hg(II) complex: structures, photophysical properties, and DFT calculations

A new ligand (L) and its mercury(II) complex have been synthesized under mild conditions. X-ray single-crystal structural analyses reveal 1-D, 2-D, and 3-D supermolecular structure of L and HgLI2. Solvent molecules and various weak interactions, including hydrogen bonds (N–H···N, O–H···O, and O–H···N) and π–π interactions play significant roles in the final supermolecular structures. Detailed investigation on 1H NMR spectra of L and HgLI2 are presented. Their photophysical properties were investigated both experimentally and theoretically.

CCDC 725513: Experimental Crystal Structure Determination

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1-(4-Carb-oxy-phen-yl)-1H-imidazol-3-ium chloride dihydrate.

In the crystal structure of the title compound, C10H9N2O2 +·Cl−·2H2O, the components are linked by O—H⋯O, N—H⋯O, O—H⋯Cl and N—H⋯Cl hydrogen bonds. In the cation, the imidazole ring is oriented at a dihedral angle of 13.67 (17)° with respect to the benzene ring. In the crystal, π–π stacking occurs between nearly parallel benzene rings, which are oriented at a dihedral angle of 3.4 (1)°, the centroid–centroid distance being 3.798 (3) Å.