Synthesis, Characterization, and Redox Property of 3-(2-Phenyl-4H-thio­chromen-4-ylidene)-3H-chromene-2,4-diones

Abstract

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.

Key words

heterocycles - oxidation - reduction - sulfur - conjugation compounds

References and Notes

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5

Crystallographic data (excluding structure factors) of compound 8 have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication number CCDC-665160. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif or by emailing [e-mail] or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: [phone].

7

Procedure for the Preparation of 13 To a solution of 12 (500 mg, 2.06 mmol) in DCE (10 mL) was added 4-hydroxy-7-N,N-dimethylaminocoumarin (423 mg, 2.06 mmol) and a catalytic amount of PTSA. After the mixture was stirred at 50 ˚C for 6 h, H₂O (5 mL) was added to the mixture and the product was extracted twice with CH₂Cl₂. The combined organic extracts were dried over anhyd MgSO₄, filtered, and concentrated. The resulting crude product was purified by column chromatography (EtOAc-hexane, 7:15) to give a blue solid with a 35% yield; mp 258-259 ˚C. ^¹H NMR (300 MHz, CDCl₃): δ = 9.62 (s, 1 H), 8.34 (dd, J = 8.4, 1.2 Hz, 1 H), 7.98 (d, J = 8.7 Hz, 1 H), 7.90 (dd, J = 8.1, 1.2 Hz, 1 H), 7.87-7.84 (m, 2 H), 7.74 (ddd, J = 8.1, 7.2, 1.2 Hz, 1 H), 7.63-7.52 (m, 4 H), 6.60 (dd, J = 9.0, 2.4 Hz, 1 H), 6.42 (d, J = 2.4 Hz, 1 H), 3.09 (s, 6 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 176.9, 165.1, 164.2, 156.48, 156.47, 155.9, 154.5, 139.1, 136.2, 134.9, 132.2, 131.8, 129.8, 129.7, 128.2, 128.0, 127.8, 126.6, 110.7, 108.4, 108.1, 97.3, 40.2. IR (KBr): ν = 1674, 1615, 1488, 1205 cm^-¹. HRMS (EI): m/z calcd for C₂₆H₁₉NSO₃: 425.1086; found: 425.1081 [M⁺].