6'-Nitro-1,3,3',4'-tetrahydrospiro[benz[e]indole-2,2'-chromene] derivatives as new ultrafast and selective cyanide receptors

Abstract Five new spiro[chromene-2,2'-benz[e]indole] derivatives were synthesized and characterized. These compounds in DMSO were found to exist as ring-chain isomers and iminium-enamine tautomers. The potential for cyanide detection was investigated. The compounds exhibited a distinct color change only when treated with cyanide ions in a CH₃CN solution buffered with sodium phosphate. In contrast, other common anions did not induce a significant color change. The detection mechanism relies on the opening of the 3,4-dihydro-2H-pyran ring and the formation of a 4-nitrophenolate chromophore, allowing for the quantitative determination of very low levels of CN⁻.