Synthesis and photophysical properties of conjugated thioketone, thioketone S-oxide (Sulfine), and related compounds incorporated in a dibenzobarrelene skeleton

Conjugated thioketone and thioketone S-oxide (sulfine) were synthesized from the corresponding ketone conjugated to a 1,3-butadiene system incorporated in a dibenzobarrelene skeleton. The conjugated thioketone was obtained by the reaction of the corresponding diazo compound with elemental sulfur, the oxidation of which with m-chloroperoxybenzoic acid provided the conjugated sulfine as a mixture of (Z)- and (E)-stereoisomers. (E)-Sulfine gradually isomerized to (Z)-sulfine in solution in the dark. Photoisomerization between (Z)- and (E)-sulfines was observed under photoirradiation together with the desulfurization to the corresponding ketone. The conjugated thioketone showed the weak long-wavelength absorption at 626 nm due to the n-π* excitation in the optical absorption spectrum and nonphotoluminescent. The conjugated (Z)-sulfine exhibited the long-wavelength absorption at 448 nm due to the π-π* excitation and very weak photoluminescence at 489 nm with the quantum yield of 0.002 at room temperature. The weak photoluminescence was enhanced in EtOH at 77 K showing yellow luminescence, and the quantum yield increased to 0.32. Lifetime values of the luminescence (2.4 and 6.8 ns) at 77 K suggests that the luminescence is fluorescence. A large solvent effect and a similar temperature dependency of photoluminescence were observed for the conjugated ketone.