Synthesis, photochromic properties and thermal bleaching kinetics of pyrazolone phenylsemicarbazones containing a thiophene ring

Abstract

Five novel pyrazolone derivatives containing a thiophene ring, 1-phenyl-3-(2-thiophenyl)-4-(3-bromobenzal)-5-hydroxypyrazole phenylsemicarbazone (1)/1-phenyl-3-(2-thiophenyl)-4-(3-chlorobenzal)-5-hydroxypyrazole phenylsemicarbazone (2)/1-phenyl-3-(2-thiophenyl)-4-benzal-5-hydroxypyrazole phenylsemicarbazone (3)/1-phenyl-3-(2-thiophenyl)-4-(4-bromobenzal)-5-hydroxypyrazole phenylsemicarbazone (4)/1-phenyl-3-(2-thiophenyl)-4-(4-chlorobenzal)-5-hydroxypyrazole phenylsemicarbazone (5), were synthesized. Among them, only two compounds (1 and 2) have excellent photochromic properties. Their structures, photochromic properties, thermal bleaching kinetics and the activation energies of the thermal bleaching process were investigated. The results show that the two compounds exhibit reversible enol–keto isomerization reaction under 365 nm light irradiation and heat, and high fatigue resistance.