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

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 365nm 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.