Synthesis, photoisomerization properties and thermal bleaching kinetics of pyrazolones containing 3-cyanobenzal

• Pyrazolone containing 3-cycanobenzal has good solid-state photochromic properties.
• Cyano in photochromic pyrazolone derivatives has the halogen-like properties.
• Pyrazolone phenylsemicarbazone exhibits excellent thermal stability.

Through the design of molecules and the modification of structures, ten novel pyrazolone derivatives containing 3-cyanobenzal have been synthesized. They are 1-phenyl-3-methyl-4-(3-cyanobenzal)-5-hydroxypyrazole thiosemicarbazone (1)/4-methyl-3-thiosemicarbazone (2)/4-ethyl-3-thiosemicarbazone (3)/4-phenyl-3-thiosemicarbazone (4)/4-phenylsemicarbazone (5) and 1,3-diphenyl-4-(3-cyanobenzal)-5-hydroxypyrazole thiosemicarbazone (6)/4-methyl-3-thiosemicarbazone (7)/4-ethyl-3-thiosemicarbazone (8)/4-phenyl-3-thiosemicarbazone (9)/4-phenylsemicarbazone (10), in which seven compounds (1, 2, 3, 6, 7, 8 and 10) have photoisomerization behaviors. Their structures, photoisomerization properties, and first-order kinetics were investigated. The results show that the compounds 2, 3, 7 and 8 exhibit irreversible photoisomerization behaviors, the other three compounds have reversible photoisomerization behaviors under 365 nm light irradiation and heat. But only 1,3-diphenyl-4-(3-cyanobenzal)-5-hydroxypyrazole 4-phenylsemicarbazone (10) exhibits good photochromic properties and fatigue resistance. Moreover, effects of various temperatures on the thermal bleaching reaction for 10 and substituent groups on the photochromic phenomenon are discussed.

Ten new pyrazolone thiosemicarbazone/phenylsemicarbazone derivatives were synthesized. Among them, 1,3-diphenyl-4-(3-cycanobenzal)-5-hydroxypyrazole 4-phenylsemicarbazone (10) exhibits excellent photochromic properties and high fatigue resistance. In addition, the decoloration reaction for compound 10 was accelerated with the increase of temperature.Figure optionsDownload as PowerPoint slide