Li-Zhen Cai

A direct white-light-emitting metal-organic framework with tunable yellow-to-white photoluminescence by variation of excitation light.

A direct white-light metal-organic framework (MOF), [AgL](n) x nH(2)O (1, L = 4-cyanobenzoate), obtained by the reaction of deprotonated 4-cyanobenzoic acid and AgNO(3) in water, was found to exhibit tunable yellow-to-white photoluminescence by variation of excitation light. Interestingly, the close pure white emission of 1 has CIE-1931 chromaticity coordinates of (0.33, 0.34) when excited by 349-nm UV light, which is compatible to the light output of the deep UV LED.

A ferroelectric inorganic–organic hybrid based on NLO-phore stilbazolium

A ferroelectric inorganic–organic hybrid based on in situ substituted stilbazolium cation (TAMS2+ = trimethylamino-N-methyl stilbazolium) has been obtained. Single-crystal X-ray structure analysis demonstrates that the NLO-phore organic component of the complex is embedded into the inorganic polymeric [Bi2Cl8]2− framework and shows a polar arrangement with the cooperation of the nonsymmetric inorganic component. The measurement of ferroelectric and nonlinear optical properties show typical ferroelectricity and second harmonic generation (SHG) responses as well as a significant improvement of the laser damage threshold and thermal stability of relative organic material.

A room-temperature X-ray-induced photochromic material for X-ray detection.

A color change: X-ray-induced photochromic species are rare and can be used for detection of X-rays. A highly robust X-ray-sensitive material with the discrete structure of a metal-organic complex has been found to show both soft and hard X-ray-induced photochromism at room temperature. A new ligand-to-ligand electron-transfer mechanism was proposed to elucidate this photochromic phenomenon.

Electron‐Transfer Photochromism To Switch Bulk Second‐Order Nonlinear Optical Properties with High Contrast

The first bulk electron-transfer photochromic compound with intrinsic second-order nonlinear optical (NLO) photoswitching properties has been synthesized. This system employs an electron-transfer photoactive asymmetric viologen ligand coordinated to a zinc(II) center.

Photochromism and Photomagnetism of a 3d–4f Hexacyanoferrate at Room Temperature

Polycyanometallate compounds with both photochromism and photomagnetism have appealing applications in optical switches and memories, but such optical behaviors were essentially restricted to the cryogenic temperature. We realized, for the first time, the photochromism and photomagnetism of 3d-4f hexacyanoferrates at room temperature (RT) in [Eu(III)(18C6)(H2O)3]Fe(III)(CN)6·2H2O (18C6 = 18-crown-6). Photoinduced electron transfer (PET) from crown to Fe(III) yields long-lived charge-separated species at RT in air in the solid state and also weakens the magnetic susceptibility significantly. The PET mechanism and changing trend of photomagnetism differ significantly from those reported for known 3d-4f hexacyanoferrates. This work not only develops a new type of inorganic-organic hybrid photochromic material but opens a new avenue for RT photomagnetic polycyanometallate compounds.

Rare electron-transfer photochromic and thermochromic difunctional compounds

Two new isostructural coordination compounds exhibit the rare difunctional properties of both electron-transfer (ET) photochromism and ET thermochromism, which are significantly affected by halogen atoms. The thermocrystallographic studies of the same single crystal have elucidated the electron-donating nature of the halogen atoms.

Tetraalkylammonium cations as templates in the construction of two cadmium(II) metal–organic frameworks

Hydrothermal reaction of cadmium salts with HATZ in the presence of R4NBr (R = Et, Pr) led to two organic cation templated Cd(II) MOFs, (Et4N)[Cd6Br5(ATZ)8]·H2O (1) and (Pr4N)[Cd4Br5(ATZ)4] (2) (HATZ = 5-amino-tetrazolate, Et = ethyl and Pr = propyl), which are the first examples of tetraalkylammonium cations templated N-heterocyclic ligand based MOFs. These two MOFs have been fully characterized by single crystal X-ray diffraction, XRD, TGA, IR, elemental analysis, photoluminescence spectra and combustion heat measurement. The anionic frameworks of 1 and 2 are three- and two-dimensional, respectively. Topological analyses show that compound 1 exhibits an unprecedented binodal (4,10)-connected network, which is a subnet of the (12,12)-connected tcj net, and compound 2 is a 2-D uninodal four-connected network when the Cd6 clusters in these two MOFs are viewed as nodes. Moreover, compound 1 maybe have potential application as an energetic material due to its high enthalpy of formation.

Two novel halogeno(cyano)argentates built by silver halide clusters: molecular structures and luminescent properties

Two novel halogeno(cyano)argentates(I), [Et4N]3[Ag6(CN)3.39Br5.61] (1) and [Pp4N]3[Ag8(CN)4I7] (2) (Et4N = tetra-ethylammonium, Pp4N = tetra-n-propylammonium), were obtained by the solvothermal reaction of silver(I) cyanide with tetraalkylammonium salts in anhydrous THF. Complex 1 presents a 2-D grid-like sheet built by [Ag6Br5]+ clusters bridged by cyanide groups. Complex 2 is the first example of 3-D halogeno(cyano)argentates(I), and displays a porous framework with fluorite (flu) topology based on [Ag4I4] and an unprecedented [Ag8I6]2+ cluster, respectively, as 4-connected and 8-connected nodes. The optical and luminescent properties of the two complexes have been investigated. On the basis of Time-dependent Density Functional Theory calculations, the emission spectrum of 1 can be assigned as metal-centred (MC) transitions, while the luminescence behavior for 2 is assumed to arise from metal-to-ligand charge-transfer (MLCT) transitions.

An electron-transfer photochromic metal–organic framework (MOF) compound with a long-lived charge-separated state and high-contrast photoswitchable luminescence

Long-lived charge-separated states and photoswitchable photoluminescence are important for many photochemical and photophysical applications. Recent studies have demonstrated the effectiveness of MOFs to achieve long-lived charge-separated states; however, the related studies are still rather rare owing to the limited numbers of photoresponsive MOFs. In this work, a new electron-transfer photochromic MOF compound, encapsulating photoactive viologen cations, was found to exhibit a charge-separated state with a lifetime value of more than 2 months, exceeding the reported values of the analogues. In addition, the photochromic process can afford a luminescence contrast up to 10 times between two stable states, which is higher than those of most known pyridine derivative-based photochromic compounds.

Reversible Single-Crystal-to-Single-Crystal Transformation and Magnetic Change of Nonporous Copper(II) Complexes by the Chemisorption/Desorption of HCl and H2O

Vapor-responsive magnetic materials are highly promising for applications as chemical switches or sensors. Compared with porous materials, nonporous species benefit in overcoming the intrinsic conflict between magnetic exchange and porosity but usually suffer from the powdering of single crystals, which hinders the understanding of the structural nature of vapor response and magnetic switch. Single-crystal-to-single-crystal (SCSC) transformation of nonporous compounds through the desorption/absorption of gaseous HCl is unprecedented. Reported here is a discrete nonporous copper(II) complex, (H3O)[K(15-crown-5)2][CuCl4], that exhibits reversible SCSC transformation and magnetic change by the chemisorption/desorption of HCl and H2O. Significant changes in the coordination number (4 ↔ 3), space group (P1̅ ↔ P21/c), color (green ↔ red), and magnetic behavior (antiferromagnetic ↔ paramagnetic) were found during the SCSC transformation.