Fluorescent Pyranoindole Congeners: Synthesis and Photophysical Properties of Pyrano[3,2-<i>f</i>], [2,3-<i>g</i>], [2,3-<i>f</i>], and [2,3-<i>e</i>]Indoles
Ainur D. Sharapov,
Ramil F. Fatykhov,
Igor A. Khalymbadzha,
Maria I. Valieva,
Igor L. Nikonov,
Olga S. Taniya,
Dmitry S. Kopchuk,
Grigory V. Zyryanov,
Anastasya P. Potapova,
Alexander S. Novikov,
Vladimir V. Sharutin,
Oleg N. Chupakhin
Affiliations
Ainur D. Sharapov
Department of Organic and Biomolecular Chemistry, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
Ramil F. Fatykhov
Department of Organic and Biomolecular Chemistry, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
Igor A. Khalymbadzha
Department of Organic and Biomolecular Chemistry, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
Maria I. Valieva
Department of Organic and Biomolecular Chemistry, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
Igor L. Nikonov
Department of Organic and Biomolecular Chemistry, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
Olga S. Taniya
Department of Organic and Biomolecular Chemistry, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
Dmitry S. Kopchuk
Department of Organic and Biomolecular Chemistry, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
Grigory V. Zyryanov
Department of Organic and Biomolecular Chemistry, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
Anastasya P. Potapova
Department of Organic and Biomolecular Chemistry, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
Alexander S. Novikov
Institute of Chemistry, Saint Petersburg State University, Universitetskaya Emb., 7/9, 199034 Saint Petersburg, Russia
Vladimir V. Sharutin
Department of Chemistry, Institute of Natural Sciences, South Ural State University (National Research University), Lenin Avenue 76, 454080 Chelyabinsk, Russia
Oleg N. Chupakhin
Department of Organic and Biomolecular Chemistry, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
This paper reports the synthesis of four types of annulated pyranoindole congeners: pyrano[3,2-f]indole, pyrano[2,3-g]indole, pyrano[2,3-f]indole, and pyrano[2,3-e]indole and photophysical studies in this series. The synthesis of pyrano[3,2-f], [2,3-g], and [2,3-e]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-f]indoles were synthesized through the Nenitzescu reaction of p-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-f] and [2,3-g]indoles. These compounds were characterized by moderate to high quantum yields (30–89%) and a large (9000–15,000 cm−1) Stokes shift. More detailed photophysical studies were carried out for a series of the most promising derivatives of pyrano[3,2-f] and [2,3-g]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-f] and [2,3-g]indoles as well as to explain their unusual geometries and electronic structures.
