Synthesis of biologically important, fluorescence active 5-hydroxy benzo[g]indoles through four-component domino condensations and their fluorescence “Turn-off” sensing of Fe( iii ) ions

• Published in: RSC advances Vol. 5; no. 65; pp. 52852 - 52865
• Main Authors: Maity, Subhendu, Kundu, Ashis, Pramanik, Animesh
• Format: Journal Article
• Language: English
• Published: 2015
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/C5RA05780A

Several highly substituted 2-pyrrolyl-2-cyanoacetamides were prepared through four-component domino condensation of various easily available 1,3-dicarbonyl compounds, amines, arylglyoxals and malononitrile. Subsequently these cyanoacetamide derivatives were converted into biologically important 5-hydroxy benzo[ g ]indoles through thermal cyclization under metal-free conditions. The synthesized 5-hydroxy benzo[ g ]indoles are fluorescence active with good quantum yields ( Φ F = ∼0.50). They also show excellent fluorescence “Turn-off” sensing of Fe 3+ ions (detection limit = ∼1.2 × 10 −6 M). The interaction of 5-hydroxy benzo[ g ]indoles with Fe 3+ ions can also be monitored through UV-Vis spectral change and naked-eye colour change in the presence and absence of UV radiation. The 1 H NMR titration unambiguously proves the formation of a complex between 5-hydroxy benzo[ g ]indoles and Fe 3+ ion through the coordination of –OH groups with the metal. The binding constant of the complex (metal : ligand = 1 : 1) has been measured using Benesi–Hildebrand equation and found to be ∼7.97 × 10 3 M −1 .