Synthesis, characterization, and redox property of 3-(2-phenyl-4H-thiochromen-4-ylidene)-3H-chromene-2,4-diones

Two 3-(2-phenyl-4H-thiochromen-4-ylidene)-3H-chromene-2,4-dione derivatives were synthesized and evaluated as reversible redox switches. The prepared purple compound 7 and blue compound 13 instantly changed to colorless when treated with sodium borohydride in methanol. The corresponding reduced 9 and 14 can be reverted to their original colors via DDQ oxidation or by air. While no fluorescence of the N,N-dimethylamino-substituted 13 was detected prior to reduction, the reduced 14 emitted blue fluorescence in methanol with a quantum yield value of 0.19.