Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 6 de 6
Mais filtros

Base de dados
Intervalo de ano de publicação
Dalton Trans ; 48(48): 17770-17779, 2019 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-31782445


Responsive molecular chromic materials have shown potential applications in molecular optical switches and sensor devices as they undergo reversible colour changes upon application of external stimuli. Herein, six host-guest coordination polymers 1-6 and one organic supramolecular compound 7 containing viologens have been synthesized under hydrothermal conditions. Compound 1 shows thermochromic behavior with a colour change from green to blue upon heating at 150 °C in air. Compounds 3, 4 and 7 display photochromic behaviors with a colour change from pale yellow to green under UV light, visible light or sunlight. The relationship between their structures and chromic behaviors has been discussed. Thermo/photochromic mechanisms have been investigated by infrared spectroscopy, powder X-ray diffraction analysis, UV-vis absorption spectroscopy, electron paramagnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. The results demonstrate the generation of viologen radicals caused by thermo/photo-induced electron transfer. It is found that compound 4 can be used as an inkless and erasable printing medium. In addition, compounds 3, 4, and 7 can be used as anti-counterfeiting materials for QR codes. Our findings demonstrate the possibility of applying thermo/photochromic coordination polymers in molecular devices.

Inorg Chem ; 56(24): 14926-14935, 2017 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-29200269


Four coordination polymers, namely, [Zn(HL1)(L2)0.5]·H2O (1), [Cd(HL1)(L2)0.5]·H2O (2), [Zn(L1)(L3)0.5]·H2O (3), and [Cd(L1)(L3)0.5] (4) (H3L1 = (3,5-dicarboxyl-phenyl)-(4-(2'-carboxyl-phenyl)-benzyl)ether, H2L2Cl2 = 1,1'-bis(4-carboxy-benzyl)-4,4'-bipyridinium dichloride, and L3Cl2 = 1,1'-dimethyl-4,4'-bipyridylium dichloride), have been synthesized hydrothermally. The structures of compounds 1-4 have been determined by single-crystal X-ray diffraction analyses, and further characterized by elemental analyses, infrared (IR) spectra, powder X-ray diffraction (PXRD) analyses, and thermogravimetric analyses. Compounds 1 and 2 display three-dimensional 2-fold interpenetrating frameworks, whereas compounds 3 and 4 exhibit two-dimensional layer structures. These compounds display photochromic behaviors from pale yellow to green under UV light, visible light, or sunlight. The photochromic mechanisms of these compounds have been studied by IR spectra, PXRD analyses, UV-vis absorption spectra, electron paramagnetic resonance spectra, density functional theory calculations, and X-ray photoelectron spectroscopy. The capabilities of compounds 1 and 2 as inkless and erasable printing media have also been tested. Moreover, the photomodulated fluorescence of these compounds has also been investigated.

Dalton Trans ; 42(29): 10617-25, 2013 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-23765391


Water oxidation is a key half reaction in the energy conversion scheme. The reaction mechanism for the oxidation of H2O to O2 catalyzed by single-Ru-substituted polyoxometalates, [Ru(III)(H2O)XW11O39](n-) (X = Si(IV), Ge(IV)), was investigated by means of density functional calculations. The electronic structure of the pre-activation intermediates indicates that the aqua ligand is prone to accommodate the proton coupled electron transfer (PCET) process to achieve the active group [Ru(V)=Oa], and the high valent oxo-ruthenium(V) species are responsible for the O-O forming event. Three possible proton acceptors were designed for the rate-determining step (Ob, Oa, and H2O), the calculated results support that the bridge Ob atom of the polytungstate ligand will act as the most favorable proton acceptor in the O-O bond formation, with an energy barrier of 28.43 kcal mol(-1). A detailed information of the peroxidic intermediates in the oxidation process was also characterized, both the peroxo-species [Ru(IV)(OO)SiW11O39](6-) and [Ru(V)(OO)SiW11O39](5-) show the six-coordinate isomer with an open terminal geometry is more favorable than the close seven-coordinate ones. In addition, the replacement of the heteroatom in XO4(n-) can effectively tune the catalytic activity of polyoxometalates, in the order of Ge(IV) > Si(IV).

Dalton Trans ; 41(37): 11361-8, 2012 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-22886001


The formation mechanism is always a fundamental and confused issue for polyoxometalate chemistry. Two formation mechanisms (M1 and M2) of the Lindqvist anion [W(6)O(19)](2-) have been adopted to investigate it's self-assembly reaction pathways at a density functional theory (DFT) level. The potential energy surfaces reveal that both the mechanisms are thermodynamically favorable and overall barrierless at room temperature, but M2 is slightly dominant to M1. The formation of the pentanuclear species [W(5)O(16)](2-) and [W(5)O(15)(OH)](-) are recognized as the rate-determining steps in the whole assembly polymerization processes. These two steps involve the highest energy barriers with 30.48 kcal mol(-1) and 28.90 kcal mol(-1), respectively, for M1 and M2. [W(4)O(13)](2-) and [W(4)O(12)(OH)](-) are proved to be the most stable building blocks. In addition, DFT results reveal that the formation of [W(3)O(10)](2-) experiences a lower barrier along the chain channel.

Teoria Quântica , Compostos de Tungstênio/química , Água/química , Ânions , Modelos Moleculares , Soluções
Dalton Trans ; 41(33): 10097-104, 2012 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-22763564


We theoretically investigate a novel switching phenomenon based on the divacant Keggin-type polyoxotungstate bearing chiral organophosphonate [{NH(2)CH(CH(3))PO}(2)(γ-SiW(10)O(36))](4-), that is the synchronous chiroptical and nonlinear optical (NLO) switch triggered by redox. The ECD calculations on the Boltzmann weighted conformations of the three oxidation states of this chiral polyoxometalate (POM) clearly present a chiroptical switching process. The electronic transition and the bond-length alternation studies show that the chirality transfer from chiral carbon atom to POM cage increases as the polyanion is reduced. Simultaneously, the static first hyperpolarizability of studied chiral POM quadrupled from the oxidized state to the 1e-reduced state, and is further doubled to the 2e-reduced state, which is mainly due to the increasing electronic-dipole-allowed d-d charge transfer transitions in the POM cage. This work firstly reproduces the ECD spectrum of chiral POM with high accuracy and proves the possibility for confirming the molecular conformations of flexible chiral POMs in solution by the aid of ECD calculations. Most importantly, a sensitive diplex switch based on a chiral POM is predicted in theory, which may aid the design of novel POM-based switches.

J Mol Graph Model ; 32: 1-8, 2012 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-21995997


In this paper, density functional theory is used to investigate the linear optical and nonlinear optical (NLO) properties of a series of Λ-type chiral compounds composed of two Lindqvist-type polyoxometalates (POMs) linked by 1,1'-binaphthyl derivatives through arylimido. It shows that compound 1 which has two POMs on 6-6'-sites of 1,1'-binaphthyl possesses large static first hyperpolarizability and the strongest two-dimensional NLO response among studied compounds. The organic substituents on 2-2'-sites of 1,1'-binaphthyl twofold control the NLO responses of studied compounds. They act as electron acceptors or donors therefore suppress or enhance the NLO responses of studied compounds, and they restrain the torsion angles between two naphthyl rings at certain degrees which are inversely proportional to the NLO responses. Compound 6 with remarkable NLO response is obtained as ferrocene substitutes on 2-2'-sites of 1,1'-binaphthyl. Additionally, the electronic circular dichroism (ECD) spectra of studied compounds are simulated with CAM-B3LYP and B3LYP hybrid functionals. The results agree well with the experimental ECD spectra. The charge-transfer transitions from organic fragment to POM are responsible for the ECD differences between molecular hybrids and their precursors. It is confirmed that these Λ-type chiral compounds are potentially high-dimensional NLO materials and the structure-property relationship of these compounds is presented.

Naftalenos/química , Compostos de Tungstênio/química , Dicroísmo Circular , Modelos Moleculares , Estrutura Molecular , Relação Estrutura-Atividade