THE ABSORPTION SPECTRA OF FLUORESCEIN, FLUORAN AND SOME RELATED COMPOUNDS¹

Abstract

The following investigation on the absorption of fluorescein was undertaken in the course of our study of triphenylmethane derivatives.3 The absorption of fluorescein has been studied extensively in the past but the recorded data show wide variations. In the earlier work,4 only solutions of alkali salts of fluorescein were employed. Meyer and Fischer5 prepared a violet solution of fluorescein by boiling it with a concentrated solution of alkali. They called attention to the similarity of its absorption spectrum with that of phenolphthalein in dilute alkaline solution. Medhi and Watson6 and Howe7 compared the absorption of neutral and alkaline solutions of fluorescein in the visible and ultraviolet regions, respectively. Howe also reported on the absorption of fluoran in neutral and alkaline alcoholic solutions. Moir8 studied the visible absorption of fluorescein in coned, sulfuric acid solution. Other reports on the absorption in the visible region were made by Nichols and Merritt,9 Formánek and Knop10 and Holmes.11The lack of concordant results can be ascribed to two causes: (1) using impure materials, such as commercial preparations or extracts made directly from the fusion mixture; (2) neglecting to mention concentrations, both of fluorescein and alkali in the case of alkaline solutions, for 1 The assistance of a grant made to the first two authors from the Heckscher Research Foundation of Cornell University which enabled us to make the measurements described in this report is gratefully acknowledged.

pH dependent spectral properties of sodium fluorescein ophthalmic solutions revisited

“…This is very different from consideration of fluorescein as a chemical and for which spectra have often been obtained in extremely alkaline and/or alcoholic solutions (e.g. Orndorff et al. , 1928).…”

The molecular structure of anionic species of 2,4,5,7‐tetranitrofluorescein as studied by electrospray ionisation, nuclear magnetic resonance and X‐ray techniques

“…The rupture of the pyran ring of fluorescein doesn't occur immediately, and the further decrease of the intensity of the band at k = 583 nm and decolorisation occurs very slowly [27]. Similar processes for 2,4,5,7-tetrabromofluorescein (eosin) and other xanthenes are also described in the literature [30][31][32].…”

“…The absorption bands of the dianions of fluorescein and phenolphthalein in aqueous solution are somewhat different, namely at k max = 490 nm and 553-555 nm, respectively. Indeed, as observed by Lewis [28], the k max data reported by Orndorff et al [27] are 10-20 nm overestimated. But the results are qualitatively correct, and are in line with the data of others [29].…”

“…Indeed, as observed by Lewis , the λ max data reported by Orndorff et al . are 10–20 nm overestimated. But the results are qualitatively correct, and are in line with the data of others .…”

“…It should be noted that the rupture of the pyran ring of the unsubstituted fluorescein occurs in very concentrated aqueous potassium hydroxide (33%) ; the band at λ = 496 nm decreases, whereas a new band at λ = 583 nm appears . The latter can be ascribed to the phthalein dye, analogous to 12 , and similar to phenolphthalein.…”