Supplemental studies on the relationship between structure and spectrum of fluorescein was written by Chen, Sheng-Chih;Nakamura, Hiroshi;Tamura, Zenzo. And the article was included in Chemical & Pharmaceutical Bulletin in 1979.Synthetic Route of C22H16O5 This article mentions the following:
The relationship between the structure and spectrum of fluorescein I in aqueous solution was investigated by comparing the absorption and fluorescence properties of I with those of monomethylfluorescein, dimethylfluorescein, and fluorescein Me ester (II). Fluorescein was predominantly present in its univalent cation, neutral lactonoid (III), univalent anion and bivalent anion (IV) forms at pH < 1, pH 3, pH 5-6 and pH > 8, resp. All form except III were fluorescent and IV fluoresced most intensely. The neutral quinonoid form was not detected in aqueous solution, contrary to results of previous authors. In the experiment, the researchers used many compounds, for example, 3′,6′-Dimethoxy-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one (cas: 36886-76-7Synthetic Route of C22H16O5).
3′,6′-Dimethoxy-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one (cas: 36886-76-7) belongs to benzofurans derivatives. Benzofuran derivatives are one of the most important oxygen-containing heterocycles. Substituted benzofurans find applications such as fluorescent sensors, oxidants, in drug discovery, and in another field of chemistry and agriculture.Synthetic Route of C22H16O5
Referemce:
Benzofuran – Wikipedia,
Benzofuran | C8H6O – PubChem