Fluorescent Pyranoindole Congeners: Synthesis and Photophysical Properties of Pyrano[3,2- f ], [2,3- g ], [2,3- f ], and [2,3- e ]Indoles

• Published in: Molecules (Basel, Switzerland) Switzerland), 2022-12, Vol.27 (24), p.8867
• Main Authors: Sharapov, Ainur D, Fatykhov, Ramil F, Khalymbadzha, Igor A, Valieva, Maria I, Nikonov, Igor L, Taniya, Olga S, Kopchuk, Dmitry S, Zyryanov, Grigory V, Potapova, Anastasya P, Novikov, Alexander S, Sharutin, Vladimir V, Chupakhin, Oleg N
• Format: Article
• Language: English
• Subjects: Aminophenol; Benzoin; Benzoquinone; Bischler–Möhlau reaction; Chemical Phenomena; Chromatography; Coloring Agents; Congeners; Fluorescence; Hydrocarbons; Indoles; Indoles - chemistry; Ketoesters; Light emitting diodes; Lippert-Mataga equation; Microscopy; Nenitzescu reaction; Pechmann condensation; pyranoindole; Solvents; Spectrum analysis; Stokes shift
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules27248867

This paper reports the synthesis of four types of annulated pyranoindole congeners: pyrano[3,2- ]indole, pyrano[2,3- ]indole, pyrano[2,3- ]indole, and pyrano[2,3- ]indole and photophysical studies in this series. The synthesis of pyrano[3,2- ], [2,3- ], and [2,3- ]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- ]indoles were synthesized through the Nenitzescu reaction of -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- ] and [2,3- ]indoles. These compounds were characterized by moderate to high quantum yields (30-89%) and a large (9000-15,000 cm ) Stokes shift. More detailed photophysical studies were carried out for a series of the most promising derivatives of pyrano[3,2- ] and [2,3- ]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- ] and [2,3- ]indoles as well as to explain their unusual geometries and electronic structures.