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.

Analysis of Association Constant for Ground-State Dye-Electron Acceptor Complex of Photoinitiator Systems and the Association Constant Effect on the Kinetics of Visible-Light-Induced Polymerizations

Abstract: We investigated the formation of ground state donor/acceptor complexes between xanthene dyes (rose Bengal (RB) and fluorescein (FL)) and a diphenyl iodonium salt (DPI) which is dissolved in 2-hydroxyethyl methacrylate (HEMA) monomer. To characterize the association constant of the complex, we have suggested a new analysis model based upon the Benesi-Hildebrand model. Because the assumption of the original Benesi-Hildebrand model is that the absorption bands are due only to the presence of the complex and that the absorption by the free component is negligible; the model cannot be applied to our systems, which is a dye-based initiator system. For each dye, the molar absorptivity of the ground state complex was evaluated as a function of wavelength and this analysis confirmed the validity of the modified Benesi-Hildebrand model. In addition, we observed the RB/DPI photoinitiator system failed to produce a perceptible polymerization rate but the FL/DPI photoinitiator system provided very high rates of polymerization. Based upon the association constant for these complexes, we concluded that the observed kinetic differences arise from the different association constant values of the ground state dye-acceptor complex, resulting in back electron transfer reaction.

Far-red to near-infrared fluorescent probes based on silicon-substituted xanthene dyes for sensing and imaging

Abstract: Far-red to near-infrared (NIR) fluorescent probes with absorption and emission in the spectral region of 600–900 nm are of high interest because of their low autofluorescence interference, deep-tissue penetration, and minimal photodamage to biological samples. In recent years, the Si-substituted xanthenes have attracted considerable attention owing to their remarkable far-red to NIR photophysical properties and biocompatible characteristics. This paper reviews the synthetic methods of silicon-substituted xanthene dyes and the progress in the development of far-red to NIR fluorescent probes based on these dyes, and introduces representative chemosensors along with their fluorescent behavior toward specific analytes. The fluorescent probes in sensing various biological species, including metal ions and anions, intracellular pH changes, reactive oxygen species (ROS) and reactive nitrogen species (RNS), as well as enzymes and other related species, were summarized. The sensing mechanisms and applications of corresponding sensors are also discussed.

Photoinitiators for photopolymerizable coating compositions

Abstract: Photopolymerizable coating compositions contain, as the binder, olefinically unsaturated compounds having a boiling point above 50° C, together with from 0.5 to 15% by weight of photoinitiators, based on the binder. The photoinitiators are a mixture of an aromatic carbonyl compound A, which is a derivative of benzoin or benzil, which has at least one carbon-oxygen single bond in the α-position relative to the carbonyl group, an aromatic carbonyl compound B which is derived from benzophenone, fluorenone, anthraquinone, xanthene, thioxanthone or acridone, and an amine C of the general formula ##STR1## where R', R" and R"' are H, alkyl of 1 to 10 carbon atoms, cycloalkyl of 3 to 10 carbon atoms, aryl, hydroxyalkyl of 1 to 8 carbon atoms or alkoxyalkyl of 2 to 4 carbon atoms, but at most 2 substituents are H and at most 2 substituents are aromatic. These coating compositions may be used for finishing various substrates, as fillers or as printing inks.

Optical properties of protonated Rhodamine 19 isomers in solution and in the gas phase

Abstract: Visible light absorption and fluorescence of three positional isomers of protonated Rhodamine 19 (o-, m- and p-R19H(+)) were studied in solution and in the gas phase. In solution, strong solvatochromic effects lead to spectral shifts between rhodamine isomers. In contrast, in the gas phase, these species were found to exhibit very similar fluorescence, while pronounced differences were observed in the absorption spectra. The o-R19H(+) was found to have the largest Stokes shift in the gas phase (around 10 nm), suggesting that an intramolecular relaxation operates in the excited electronic state for this isomer. Several mechanisms for this relaxation are proposed, such as the change of the dihedral angle between the carboxyphenyl group and the xanthene chromophore or that between the carboxylic group and the phenyl ring.