Solid-state photochromic behavior and thermal bleaching kinetics of two novel pyrazolone phenylsemicarbazones

Abstract

Two novel photochromic compounds, 1,3-diphenyl-4-benzal-5-hydroxypyrazole 4-phenylsemicarbazone (1a) and 1,3-diphenyl-4-(4-nitrobenzal)-5-hydroxypyrazole 4-phenylsemicarbazone (2a), are synthesized and characterized by elemental analysis, mass spectrometry, FTIR spectroscopy, and 1H NMR spectroscopy. Their properties, including photochromic behavior, fluorescence properties, and thermal bleaching kinetics, are investigated. The results show that the two compounds exhibit improved photochromic performance in coloration and thermal bleaching rates, excellent photostability, high fatigue resistance, and reversible fluorescence switching properties in the solid state in comparison to reported pyrazolone thiosemicarbazones. The thermal bleaching process obeys first-order kinetics. Bleaching of powders at 130°C is completed within 90 s for 1b (the colored isomer of 1a) and 150 s for 2b (the colored isomer of 2a). The activation energy for the thermal bleaching process is determined to be 69 and 95 kJmol-1, with frequency factors of 9.5× 107 and 9.4× 1010 s-1 for 1b and 2b, respectively. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.