Yiman Zhang

Direct arylation of unactivated aromatic C–H bonds catalyzed by a stable organic radical

A stable zwitterionic radical can catalyze direct arylation of unactivated aromatic C-H bonds via a chain homolytic aromatic substitution mechanism in the presence of potassium tert-butoxide.

Stacking-induced white-light and blue-light phosphorescence from purely organic radical materials

The internal salt and the sodium salt based on a new purely organic radical material exhibit stacking-induced white-light and blue-light phosphorescence, respectively, and possess moderate quantum yields. The high solubility in water makes them promising candidates for potential applications in OLEDs, especially as white-LEDs.

Anion–π interactions in new electron-deficient π systems: the relevance to solid phosphorescent colors

We herein report a new electron-deficient π system, namely carboxycarbonyl substituted imidazo[1,2-a]pyridinium, which exhibits various noncovalent interactions (hydrogen bonding, anion–π and η1-type anion–π) with chloride or perchlorate anion. Crystallographic results demonstrate that the interaction types of chloride anion and π receptor systems can be tuned: from anion–π interactions (with guest methanol molecule in crystal) to η1-type anion–π interactions (without guest methanol molecule in crystal). These carboxycarbonyl substituted imidazo[1,2-a]pyridinium salts also exhibit different phosphorescent colors in the solid state induced by crystal stacking structures or anion–π interactions that can influence the charge transfer to electron-deficient carboxycarbonyl substituted imidazo[1,2-a]pyridinium. Especially, the solid phosphorescent color changes induced by anion–π interactions are very interesting. The high solubility in water makes these purely organic phosphorescent materials promising candidates for potential applications.

Magnetic and luminescent properties of Cd(II)- and Fe(II)-anion radical frameworks: various networks or structures influenced by metal ion sizes or in situ forming mechanisms of anion radical ligand

The preparation, X-ray crystallography, EPR, and magnetic and luminescent properties of three new metal–anion radical frameworks are described herein. The anion radical ligand (bipo−˙) and co-ligand, 1,4-benzenedicarboxylate (BDC2−), coordinate to Cd(II) centers, leading to an interpenetrated three-dimensional (3D) metal–organic frameworks (MOF), [Cd3(bipo−˙)4(BDC)]n (1). Although [Fe3(bipo−˙)4(BDC)]n (2) and 1 possess the same space group (tetragonal, P42/nbc), and similar rigid spirocycle-like chain and powder X-ray diffraction (PXRD) patterns, 2 exhibits an interesting spirocycle-like one-dimensional (1D) chain network, in which BDC2− behaves not as bridging co-ligand but as a counteranion, according to smaller Fe(II) ion size and long Fe1⋯Fe1′ distance between rigid chains. Thus, metal ion sizes induce different networks of isomorphous 1 and 2. Moreover, the different forming mechanisms of bipo−˙ ligand also result in different structural MOFs: the in situ deprotonation of initial Hbipo−˙ leads to an 1D Fe(II) MOF (2); the in situaldol condensation and then deprotonation of initial hydrochloride salt of imidazo[1,2-a]pyridin-2(3H)-one results in a two-dimensional (2D) Fe(II) MOF, [Fe3(bipo−˙)2(μ2-OH)2(μ2-H2O)(BDC)]n (3). More noteworthy, in 2, BDC2− suffers large distortion, mainly attributed to its strong electrostatic interaction with the Fe(II) cation on the rigid spirocycle chain. Compounds 2 and 3 exhibit broad EPR signals, ascribed to the strong iron–anion radical antiferromagnetic coupling. 1 shows an unusual magnetic phase transition at ∼70 K, and intense fluorescence emission which can even be excited by visible light (460 nm). Both 2 and 3 show strong antiferromagnetic interaction between Fe(II) cation and radical. Compared to 1, two Fe(II) MOFs exhibit obvious blue-shift fluorescence emissions.

Excitation-light-responsive phosphorescent color changes in a β-cyclodextrin inclusion complex

Herein, we report a novel supramolecular phosphorescent material based on a β-cyclodextrin inclusion complex. This inclusion complex exhibits unprecedented excitation-light-responsive phosphorescent color changes, which is a promising candidate for dynamically photofunctional material.

Hydrothermal syntheses, crystal structures and properties of novel quinone biradical and mixed-valence copper coordination polymer with semiquinone radical ligand generated in situ

A novel quinone biradical (1) was hydrothermally synthesized through ZnCl2 mediated decarboxylation and carbon–carbon coupling reactions using the 2-(imidazo[1,2-a]pyridin-2-yl)-2-oxoacetic acid radical. Interestingly, when CuCl2 was used instead of ZnCl2, a new mixed-valence copper coordination polymer (2) with semiquinone radical anion ligand was obtained. The possible formation mechanism of these two compounds is proposed. The EPR and magnetic susceptibility data suggest that 1 is a biradical. The EPR and XPS results support that 2 is a mixed-valence copper coordination polymer. The quinone biradical 1 forms a one-dimensional (1D) columnar stacking chain. The coordination polymer 2 consists of a two-dimensional (2D) layered framework constructed by 1D corrugated double-stranded stair-like inorganic [CuCl]n chains and bridged semiquinone radical anion ligands. 1 and 2 exhibit antiferromagnetic coupling interactions and different luminescent colors.