Structure of red and orange fluorescein

Abstract

The structures of colorless, red, and yellow-orange fluorescein have been investigated by a combination of solution and solid state 13C NMR. It is demonstrated that the three forms have lactonic, zwitterionic, and quinoid structures, respectively. Conflicting X-ray, NMR, and IR structural evidence is discussed for samples of red fluorescein which cannot readily be obtained in definite crystalline form. It is concluded that solid-state 13C NMR spectroscopy is superior by revealing primarily the molecular structure but being fairly insensitive toward lattice variations.

Ratiometric and selective fluorescent chemodosimeter for Cu(II) by Cu(II)‐induced oxidation

“…The characteristic peak at 66 ppm in 13 C-NMR spectra of 1 in CD 3 CN also supported this consideration (24). However, the addition of Cu(II) to the solution of 1 caused a simultaneous enhancement of absorbance at 560 nm and a fluorescence redshift from 515 to 585 nm, indicating that the spirolactam ring was opened by Cu(II) as expected.…”

A Novel Chemosensor Based on Rhodamine Derivative for Colorimetric and Fluorometric Detection of Cu2+ in Aqueous Solution

“…The total concentration of 2 and Cu 2+ was kept at a fixed 20 μM. The absorbance was measured at 527 nm characteristic peak at 66.5 ppm (spiro carbon) in the 13 C NMR spectrum of 2 also supports this consideration [30]. The addition of various metal ions such as Ag + , Al 3+ , Ba 2+ , Ca 2+ , Cd 2+ , Co 2+ , Cr 3+ , Fe 3+ , Hg 2+ , K + , Mg 2+ , Mn 2+ , Ni 2+ , Pb 2+ , Zn 2+ have little change to the UV-vis spectrum of chemosensor 2 and the color of the solutions containing these ions remained relatively unchanged.…”

Functionalization of magnetic nanoparticles with organic molecules: Loading level determination and evaluation of linker length effect on immobilization

“…This was supported by 13 C-NMR, as a new signal around 97 ppm was observed corresponding to the quaternary spiro carbon. 48 These rhodamine B derivatives fully regained the conjugation and color when TFA was added to the solution as evident from UV-vis spectra (Fig. 2a).…”