The effect of ring size on the optical behavior of novel photochromic push-pull dyes.

The photophysical behaviors of newly synthesized photochromic dyes have been investigated in different solvents of various polarities using steady-state absorption and emission techniques. It was found that, the absorption and emission spectra of these dyes depend on the ring size and the solvent polarity. The higher values of the dipole moments of the investigated dyes in the excited state than those in the ground state suggest that these dyes can serve as good candidate components of nonlinear optical materials. Additionally, the photoisomerization parameters (percentage of composition of cis isomers and quantum yields of photoisomerization) depend on the polarity and the viscosity of the used solvents as well as the ring size. The molecular motion that occurs in the isomerization process has facilitated the development of molecular devices. Finally, the halochromic behaviors of the investigated dyes promise them to act as acid-base indicators.

Spectroscopic properties and the catalytic activity of new organo-lead supramolecular coordination polymer containing quinoxaline.

The 3D-supramolecular coordination polymer (SCP) (3)∞[ Cu2(CN)3(Me3Pb)(qox)], 1, as the first example of the CuCN SCP containing the (Me3Pb) fragment, was explored to investigate its catalytic and photo-catalytic activities. The structure of 1 contains two chemically identical but crystallographically different [Cu2(CN)3⋅Me3Pb⋅qox]2 units with four Cu(I) sites assuming distorted TP-3 geometry. Two non-linear chains of equal abundance are formed producing corrugated parallel chains which are connected laterally by quinoxaline creating 2D-layers which are arranged parallel in an (AB⋯AB⋯AB)n fashion forming 3D-network. IR, mass, electronic absorption and fluorescence spectra are also investigated. The SCP 1 is diamagnetic and exhibits good catalytic and photo-catalytic activities for the degradation of methylene blue (MB). The reaction is first order with respect to MB dye. The irradiation of the reaction with UV-light enhanced the rate of MB mineralization. The efficiency of recycled the 1 and the mechanism of degradation of MB dye were investigated.

Structure and applications of metal-organic framework based on cyanide and 3,5-dichloropyridine.

The reaction of the aqueous/acetonitrile solutions of K3[Cu(CN)4] and 3,5-dichloropyridine (3,5-dClpy), in the presence of Me3SnCl affords a new metal-organic framework (MOF), (3)∞[(CuCN)2·(3,5-dClpy)2], 1. The structure of the MOF 1 was characterized by IR, UV-visible, TGA and X-ray single crystal analysis. The structure of MOF 1 consists of CuCN building blocks which are connected by CN group forming 1D-zig-zag chains. Each chain is bridged to another chain by hydrogen bonding organizing 2D-sheets. The structure of 1 is further close packed by hydrogen bonds, π-π stacking and lp-π interactions creating 3D-network. The emission spectra and the thermodynamic parameters from TGA of the MOF 1 were discussed. The MOF 1 was used as heterogeneous catalyst for the oxidative discoloration of methylene blue dye (MB) by dilute solution of hydrogen peroxide as oxidant. The in vitro cytotoxic activity has been evaluated against the human breast cancer cell lines MCF-7. The cytotoxic effect of the MOF 1 on the viability of MCF-7 cells was determined by MTT assay.

A novel hydrogen bonded bimetallic supramolecular coordination polymer {[SnMe3(bpe)][Ag(CN)2] · 2H2O} as anticancer drug.

The reaction of Me(3)SnCl, K(3)[Ag(CN)(4)] and 1,2-bis(4-pyridyl)ethane (bpe) in water/CH(3)CN solution at room temperature affords the novel bimetallic supramolecular coordination polymer (SCP) {[SnMe(3)(bpe)] [Ag(CN)2] · 2H(2)O}(n), 1. The structure of 1 consists of cationic {-Sn(Me(3))-bpe-}(+) chains that are neutralized by [Ag(CN)(2)](-) anions. The dicyanoargentate(I) anions present discrete uncoordinated fragments between the cationic chains. The water molecules bind the cationic chains and the anions forming 3D-supramolecular structure through hydrogen bonds. 1 exhibits strong fluorescence in the solid state at room temperature. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to determine the in vitro antitumor effects of the SCP 1 on human breast cancer cell line, T-47D. Cell cycle analysis revealed that the SCP 1 induced apoptosis in T-47D breast cancer cell line. Moreover, in vivo, the SCP 1 showed tumor growth inhibition in rat model that developed mammary carcinoma by 44.8% compared to the vehicle treated control. Thus, the SCP 1 exhibits specific in vivo and in vitro antitumor effects.

Fluorescence characteristics and photostability of benzoxazole derived donor-acceptor dyes in constrained media.

The spectroscopic properties and photoreactivity of 2-(4-dimethylaminostryl)benzoxazole and its butadienyl analogue (abbreviated as DMASBO and BODB, respectively) were investigated in thin films of PS, PMMA and PVA polymer matrices as well as immobilized on silica surface. The experimental results showed that the investigated benzoxazole derivatives are sensitive to the polarity of its microenvironment even in the glassy matrices and in the solid state. The micropolarity of PVA and silica surface is greater than that of PMMA and PS. The combined results of fluorescence quantum yield and photoisomerization indicated that the size of the free volume within the polymer matrix influence strongly the photochemical reactivity of the used dyes. In PVA, which offers the smaller free volume, the photoreaction is totally blocked while the fluorescence yield is extremely enhanced relative to those in solutions and other polymer matrices. This is associated with an emission of green laser from DMASBO-PVA doped film when pumped by nitrogen laser (337 nm). The results showed that the present dyes are excellent probes for non-fluorescent systems presenting constrained geometry. The spectra of amorphous solid thin films of both dyes were also measured and show large red shifts relative to those in solutions indicating symmetric aggregation of molecules in the solid crystals.

New approach for evaluation optical absorption measurements of charge transfer complexes between dimethoxynaphthalenes and tetracyanoethylene: singular value decomposition method.

Singular-value decomposition (SVD) method is a numerical multidimensional technique appropriate for evaluation of optical absorption measurements of 1:1 charge transfer complexes (CTCs). Matrix algebra of the absorption data for different solutions and wavenumbers is primarily used for evaluation of the equilibrium constant and to obtain some general expressions to illustrate physical significance of the results obtained. The influence of the ratio of the concentrations of donor and acceptor is examined. It can lead to information about the stoichiometry of the complex formed in solution. Calculations on data for CTCs between dimethoxynaphthalene (DMNs) and tetracyanoethylene (TCNE) in CH2Cl2 at various temperatures are described. The results suggest that there is a noticeable difference in the K4, caused by substitutions at alpha- and beta-positions, because the alpha-position of naphthalene exhibits relatively high electron density compared with the corresponding beta-position. There is a linear correlation between the donor HOMO energy and charge-transfer absorption maxima.

Fluorescence decay of singlet excited-state of safranine T and its interaction with ground-state of pyridinthiones in micelles and homogeneous media.

The fluorescence decays of safranine T were studied in different homogeneous solvents and heterogeneous micellar solutions. It has been found that micellization leads to an increase in the lifetime. The lifetime distributions were studied in micelles and homogeneous media. It was found that the different half-width distributions of the dye in different micelles are related to the different orientation of the dye in different micelles. Also, the fluorescence quenching of safranine T by 4,6-disubstituted-3-cyanopyridin-2(1H)-thiones was studied in chloroform, methanol and acetonitrile as well as in different micelles. In heterogeneous media the kq values for quenching of safranine T by thiones in various micelles increase on the following order: kq(CTAB) < kq(TX-100) < kq(SDS). This is due to the electrostatic interactions between the anionic SDS and the cationic moiety of safranine T and therefore the quenching process will be less significant.