Excited-state intramolecular proton transfer on 2-(2'-hydroxy-4'-R-phenyl)benzothiazole nanoparticles and fluorescence wavelength depending on substituent and temperature.

The fluorescence emission properties of 2-(2'-hydroxy-4'-R-phenyl)benzothiazole (HBT-R) nanoparticles with different substituents (R = -COOH, -H, -CH(3), -OH, and -OCH(3)) were investigated using spectroscopic and theoretical methods. HBT-Rs displayed dual enol and keto (excited-state intramolecular proton transfer (ESIPT)) emissions in nonpolar solvents. The spectral change of their ESIPT emissions was affected differently by the electron donating (or withdrawing) power of the substituents; a bathochromic shift for the electron donating group and a hypsochromic shift in electron withdrawing group. In addition, the changes in energy levels calculated by the ab initio method were consistent with the spectral shifts of HBT-R in solution. We prepared aggregated HBT-R nanoparticles using a simple reprecipitation process in tetrahydrofuran-water solvents. The ESIPT emission of aggregated HBT-R nanoparticles was strongly enhanced (over 45 times) compared to those of monomer HBT-Rs in toluene, as markedly shifted ESIPT emissions are observed at longer wavelength without any quenching by self-absorption. Aggregated HBT-R nanoparticles showed longer lifetimes than those of monomer molecules. The temperature effect on the aqueous dispersion of the aggregated HBT-R nanoparticles was also explored. It shows a fluorescent ratiometric change in a range of temperature from 7 to 65 degrees C. A mechanism of a temperature-dependent equilibrium between the nanoparticles and the solvated enols is proposed for the emission color change.

Di-micro-acetato-O:O'-di-micro-acetato-O,O':O'-bis{[(cyclopentadienyl)tris(dimethylphosphito-P)cobalt-O,O',O"]neodymium(III)}

In the title compound, [{eta(5)-CpCo[P(O)(OMe)(2)](3)}Nd(O(2)CCH(3))(2)](2), with a centrosymmetric molecule, each Nd atom has an eight-coordination environment, surrounded by a tripodal {L(OMe) = CpCo[P(O)(OMe)(2)](3)} and four bridging acetato ligands. The coordination geometry around each Nd centre is described as a distorted square-antiprism and the two different types of acetato ligands have micro-O:O'- and micro-O,O':O'-acetato coordination modes. The Nd-O distances are in the range 2.378 (4)-2.594 (5) A and the Nd.Nd distance is 3.9913 (6) A.

Synthesis of a Five-Membered Molecular Necklace: A 2+2 Approach.

Like with a string of pearls, four molecular "beads" are threaded on a molecular rectangle to form a molecular necklace. This rectangular species is synthesized from two L-shaped, preorganized pseudorotaxanes with two molecular beads each (cucurbituril, schematically symbolized by the barrels), held together by Cu2+ ions [Eq. (1)].