Absorption and Fluorescence Spectra of Halogen Derivatives of Fluorescein

Abstract

The effects of hydrogen ion concentration on the absorption and fluorescence spectra of six halogen derivatives of fluorescein (DC'F, TCF, TB'F, TI'F, DCTB'F, TCTB'F) were studied in water-dioxan mixed solvent. These halogen derivatives may have four ionic forms in solution, i. e., monovalent cation, neutral form, monovalent anion and divalent anion. Absorption and fluorescence bands in various solutions were assigned to these ionic forms, and dissociation equilibrium constants, K, were calculated. The stronger the electron attractive force of halogen, the smaller is the pK value. For absorption spectra, the bathochromic effect of halogen atoms was observed and the effect in divalent anions was larger than that in monovalent cations. A red shift of fluorescence spectra (bathochromic shift) was also observed. Decrease of fluorescence intensity by heavy atoms in monovalent cations was larger than that in divalent anions.