Chiroptical Properties and the Racemization of Pyrene and Tetrathiafulvalene-Substituted Allene: Substitution and Solvent Effects on Racemization in Tetrathiafulvalenylallene

Dissymmetric 1,3-diphenylallene derivative 3 connected with 4,5-bis(methyl-thio)tetrathiafulvalenyl and 1-pyrenyl substituents was prepared and characterized. The molecular structure was determined by X-ray crystallographic analysis. Optical resolution was accomplished using a recycling chiral HPLC, and its chiroptical properties were examined with optical rotation and electronic circular dichroism (ECD) spectra. The title compound underwent photoracemization under daylight. This behavior was investigated in various solvents and compared with that of 1,3-bis(tetrathiafulvalenyl)allene (bis-TTF-allene) derivative 2. The first-order rate plot of the intensity of the ECD spectra at a given time interval gave the rate of racemization. Mild racemization was observed in polar solvents, whereas a relatively fast rate was obtained in less polar solvents. In addition, the TTF groups of the allene also accelerate the racemization rate. These results suggest that the racemization mechanism occurs via a non-polar diradical structure

Maintaining of the Green Fluorescence Emission of 9‑Aminoanthracene for Bioimaging Applications

The green fluorescence emission of 9-aminoanthracence (<b>9AA</b>) was maintained by controlling the oxidation of <b>9AA</b> with oxygen in the solid state and in solution. The solid-state fluorescence of <b>9AA</b> was maintained for a longer time when lauric acid was used because the equilibrium between <b>9AA</b> and 9-anthrylammonium salt (<b>9AAH</b>^<b>+</b>) inclines toward the right-hand side in the presence of an acid. A solution of <b>9AA</b> in CDCl₃, to which nitrogen had been bubbled through for 5 min, continued to emit green fluorescence for more than 3 days, whereas the fluorescence emission disappeared within 3 days for the solution that had been bubbled with oxygen for 5 min. <b>9AA</b> is oxidized by oxygen in MeOH under dark conditions to give almost nongreen fluorescent anthraquinone monoimine (<b>AQNH</b>), whereas dimerization of <b>9AA</b> occurs under UV irradiation at 365 nm, much faster than the generation of <b>AQNH</b>. These results suggest that <b>9AA</b> is oxidized by the triplet rather than the singlet oxygen in MeOH. Some of the organic molecules, proteins, and biological tissues were successfully stained with <b>9AA</b> on microscope slides within 10 min because the green fluorescence emission of <b>9AA</b> was successfully maintained in the presence of an acid and under hypoxic conditions of the used materials