Xanthene

About: Xanthene is a research topic. Over the lifetime, 2132 publications have been published within this topic receiving 34803 citations. The topic is also known as: Xanthene & dibenzo[a,e]pyran.

Orientation and conformation of octadecyl rhodamine B in hybrid Langmuir-Blodgett monolayers containing clay minerals

Abstract: To control the molecular organization of octadecyl rhodamine B (RhB18), hybrid Langmuir–Blodgett monolayers containing clay minerals were prepared. The orientation and conformation of the RhB18 molecule were analyzed by polarized attenuated total reflection Fourier transform infrared (ATR–FTIR) spectroscopy and fluorescence spectroscopy. Monomers and dimers of RhB18 were observed by UV-Vis absorption spectroscopy. Infrared bands of RhB18 exhibited dichroism and shifted to higher or lower wavenumbers in films as a function of clay content. The main fluorescence band of RhB18 was more intense and shifted to lower wavelengths in films with higher clay content. In films without clay, the phenyl group of RhB18 is tilted relative to the xanthene group and both groups are tilted relative to the substrate. In films with clay, both the phenyl group and xanthene group are oriented parallel to the clay surface which is parallel to the substrate. The clay mineral surface induces a change in the conformation and orientation of the RhB18 chromophore.

Macrocycle-derived functional xanthenes and progress towards concurrent detection of glucose and fructose.

Abstract: The detection of saccharides in biological media is of great current importance for the monitoring of disease states. We have previously reported that solutions of boronic acid-functionalized macrocycles form acyclic oligomeric materials in situ. The oligomers contain fluorescent xanthene moieties. Current efforts are aimed at modulating the spectroscopic responses of these materials for the analysis of specific sugars. We describe conditions whereby the xanthene boronic acids exhibit high colorimetric fructose selectivity. In contrast, at physiological levels selective glucose monitoring can be achieved via fluorescence. Additionally, we describe a method which exhibits promise for detecting both glucose and fructose at dual wavelengths in the UV-Vis region. Mechanistic rationale for each of these findings is presented.

Quantum Mechanics Calculations on Rhodamine Dyes Require Inclusion of Solvent Water for Accurate Representation of the Structure

Abstract: DFT studies of structural and electrostatic properties of two rhodamines are reported. For one compound, a sulforhodamine, a crystallographic structure determination was used to validate the computational approach. For the other compound, N,N,N‘,N‘-tetramethylrhodamine, we considered both its lactone and quinonoid forms. Geometry optimization of the quinonoid form required inclusion of solvent effects to prevent its collapse into the lactone. Best agreement with the experimental preference for the quinonoid form in solvents of high polarity was obtained when explicit water molecules were added to a continuous solvent model. The quinonoid structures of both rhodamines are rather rigid molecules, with a strong charge separation mostly localized around the N atoms (positive pole) and around the sulfonate or carboxylate groups (negative pole). In the quinonoid structures, rotation around the N−C(xanthene) bond is considerably restricted by extensive conjugation of the N atoms with the xanthene ring. The lacto...

Cyclic triureas—synthesis, crystal structures and properties

Abstract: The synthesis of 24-membered macrocycles is described, in which rigid xanthene units (X) and/or diphenyl ether units (D) as flexible analogues are linked viaurea groups. All four possible combinations (XXX, XXD, XDD, DDD) have been obtained with yields of 40–72% for the cyclisation step. In two cases, the respective cyclic hexamers (XXDXXD, XXXXXX) were also isolated. Two compounds have been characterised by a single crystal X-ray analysis of the free triurea (XXD, XDD) and one example (DDD) by its complex with tetrabutylammonium chloride. It shows the chloride anion in the centre of the macrocycle, held by six NH⋯Cl−hydrogen bonds. The interaction with various other anions has been studied by 1H NMR. Complexation constants for chloride, bromide and acetate have been measured for all trimers by UV spectrophotometry. Molecular dynamics simulations have been carried out to determine the conformation of the free receptors in chloroform and acetonitrile. They show that in chloroform, intramolecular hydrogen bonding occasionally facilitated by trans→cisisomerisation of an amide bond dominates the conformation of the macrocycles while in acetonitrile (the solvent used for complexation measurements), the ligating urea NH protons are properly arranged for the complexation of anions, however, their strong solvation is counteractive to the complexation.

Synthesis of Dendritic Oligo-Spiro(fluorene-9,9'-xanthene) Derivatives with Carbazole and Fluorene Pendants and their Thermal, Optical, and Electroluminescent Properties.

Abstract: Two novel spiro-configured ter(arylene-ethynylene) derivatives, TSF-Cz and TSF-F, have been designed and synthesized using spiro(fluorene-9,9'-xanthene) (SFX) as building blocks, introducing a hole-transporting carbazole and a fluorene chromophore as the peripheral functional group into the backbone through an oxygen atom. The two well-defined oligomers possess good solubility, film-forming quality, and high T(g) 's at 140 and 126 °C, respectively. In addition, these oligomers exhibit blue photoluminescence (PL) emission both in solution and solid states. The double-layered devices fabricated using the two materials as the emitter show a sky-blue emission with a brightness and a current efficiency of 7 613 cd · m(-2) and 1.11 cd · A(-1) for TSF-Cz, and 1 507 cd · m(-2) and 0.36 cd · A(-1) for TSF-F, respectively.