LAUSR

A dual-responsive photochromic compound, 1,3-diphenyl-4-(3-chloro-4-pyridylformyl)-5-hydroxypyrazole 4-phenylsemicarbazone (1) based on a pyrazolone derivative with excellent reversible photochromic reactions in the crystalline state, was successfully synthesized. The new photochromic mechanism of 1 is attributed to isomerization between the enol form and keto form with proton transfer, which was confirmed by IR, XPS, crystal structure data and theoretical calculation. In order to achieve high-contrast fluorescence switch capability, two-component composite materials (TCCM) were prepared by co-aggregating. The emission intensity of fluorophore 9,10-diphenylanthracene (DPA) can be efficiently switched by the fluorescence resonance energy transfer (FRET) between the donor DPA and acceptor coloured 1 in TCCM. The fluorescence modulation ratio is found to be 79%, which is influenced by changing the content of DPA. This novel photoswitchable TCCM may have potential application as photoswitches.