| Summary: | This paper reports the synthesis of four types of annulated pyranoindole congeners: pyrano[3,2-<i>f</i>]indole, pyrano[2,3-<i>g</i>]indole, pyrano[2,3-<i>f</i>]indole, and pyrano[2,3-<i>e</i>]indole and photophysical studies in this series. The synthesis of pyrano[3,2-<i>f</i>], [2,3-<i>g</i>], and [2,3-<i>e</i>]indoles involve a tandem of Bischler–Möhlau reaction of 3-aminophenol with benzoin to form 6-hydroxy- or 4-hydroxyindole followed by Pechmann condensation of these hydroxyindoles with β-ketoesters. Pyrano[2,3-<i>f</i>]indoles were synthesized through the Nenitzescu reaction of <i>p</i>-benzoquinone and ethyl aminocrotonates and subsequent Pechmann condensation of the obtained 5-hydroxyindole derivatives. Among the pyranoindoles studied, the most promising were pyrano[3,2-<i>f</i>] and [2,3-<i>g</i>]indoles. These compounds were characterized by moderate to high quantum yields (30–89%) and a large (9000–15,000 cm<sup>−1</sup>) Stokes shift. More detailed photophysical studies were carried out for a series of the most promising derivatives of pyrano[3,2-<i>f</i>] and [2,3-<i>g</i>]indoles to demonstrate their positive solvatochromism, and the data collected was analyzed using Lippert-Mataga equation. Quantum chemical calculations were performed to deepen the knowledge of the absorption and emission properties of pyrano[3,2-<i>f</i>] and [2,3-<i>g</i>]indoles as well as to explain their unusual geometries and electronic structures.
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