Xanthene dyes can be appended to cyclodextrins via an ester or amide bridge in order to switch the fluorescence on or off. This is made possible through the formation of nonfluorescent lactones or lactams as the fluorophore can reversibly cyclize. In this context we report a green approach for the synthesis of switchable xanthene-dye-appended cyclodextrins based on the coupling agent 4-(4,6-dim...

We individuate a photoinduced electron transfer (PeT) as a quenching mechanism affecting rhodamine B photophysics in solvent. The PeT involves an electron transfer from the carboxylate group to the xanthene ring of rhodamine B. This is finely modulated by the subtle balance of coulombic and non-classical interactions between the carboxyphenyl and xanthene rings, also mediated by the solvent. We...

The title compound, C25H29ClO4, adopts a trans conformation about the C=C double bond and the di-methyl-cyclo-hexenone rings both show an envelope conformation with the dimethyl-substituted C atom as the flap. In the mol-ecule, the hy-droxy and carbonyl groups form two intra-molecular O-H⋯O hydrogen bonds typical for xanthene derivatives. In the crystal, weak C-H⋯O hydrogen bonds link the mol-e...

Two cyclic oligoureas with 64- and 80-membered rings in which two sets of three or four rigid xanthene (X) units are connected via flexible diphenyl ether (D) units were synthesized by a stepwise fragment condensation. The compounds were characterized by (1)H NMR and ESI mass spectrometry. The structure of the cyclic octamer (XXXDXXXD) was additionally confirmed by single crystal X-ray analysis...

A simple and efficient procedure for the synthesis of 14-aryl-14H-dibenzo[a,j ]xanthene derivatives through one-pot condensation of 2-naphthol with aryl aldehydes in the presence of niobium pentachloride is described. The reactions were carried out using 25 mole % of NbCl5, at ambient temperature, and in acceptable reaction times, affording excellent yields of the products. c © 2014 Institute o...

In the xanthene ring system in the title compound, C19H18O4, the 4H-pyran ring has a maximum deviation of 0.110 (2) Å from planarity and the cyclo-hexene ring exhibits a puckered conformation [puckering parameters Q T = 0.452 (3) Å, θ = 57.0 (4) and ϕ = 131.7 (4)°]. The cyclo-hexene ring attached to the xanthene system adopts an envelope conformation, with the middle of the three methylene C at...

The rhodamine system is a flexible framework for building small-molecule fluorescent probes. Changing N-substitution patterns and replacing the xanthene oxygen with a dimethylsilicon moiety can shift the absorption and fluorescence emission maxima of rhodamine dyes to longer wavelengths. Acylation of the rhodamine nitrogen atoms forces the molecule to adopt a nonfluorescent lactone form, provid...

We have investigated the kinetics of novel carbon-to-metal hydrogen atom transfer reactions, in which homolytic cleavage of a C-H bond is accomplished by a single metal-centered radical. Time-resolved IR spectroscopic measurements revealed efficient hydrogen atom transfer from xanthene, 9,10-dihydroanthracene, and 1,4-cyclohexadiene to Cp(CO)2Os(•) and (η(5)-(i)Pr4C5H)(CO)2Os(•) radicals, forme...

An efficient route is reported to 5- and 6-carboxy-X-rhodamines (compounds 1 and 2) that contain multiple n-propylene or gamma,gamma-dimethylpropylene groups bridging terminal nitrogen atoms and the central xanthene core. Gram quantities of these dyes are synthesized from inexpensive starting materials. The isolated products are activated by selective transformation of the carboxylic acid group...