title: Photochromism of an anticonvulsant, 1-diphenylmethyl-4-(6-methyl-2-pyridylmethylene-amino) piperazine, in the solid state.
abstract: The light-induced color change of 1-diphenylmethyl-4-(6-methyl-2-pyridylmethyleneamino) piperazine in the solid state was investigated. Light in the 420-700-nm visible region had no effect. Elevated temperature, dissolution, or prolonged storage in the dark at room temperatures restored the intrinsic color of the compound. IR, UV (solution), NMR, differential scanning calorimetry, and GC methods showed no detectable difference between the long wave-length UV light-exposed (yellow) and unexposed (colorless) samples of the pure compound. Long wavelength UV light exposure studies with several substituted piperazine analogs revealed a structure-activity requirement for the color conversion process. The data indicated that the transformation process from colorless (or faint yellow) to bright yellow is photochromism (phototropy) and is dependent on the intensity of the "action spectrum" in the 300-400-nm region. Studies in the solid state showed that heat-induced fading of the color followed apparent zero-order kinetics. The energy of activation, Eb, for the photochromic conversion process from the metastable (yellow) to the stable (colorless) state was estimated to be about 19 kcal/mole.
mesh_terms: D000927:Anticonvulsants; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003116:Color; D007700:Kinetics; D008027:Light; D010777:Photochemistry; D010879:Piperazines / Q000032:analysis* / Q000528:radiation effects; D011725:Pyridines / Q000032:analysis* / Q000528:radiation effects; D013329:Structure-Activity Relationship
chemical_list: D000927:Anticonvulsants; D010879:Piperazines; D011725:Pyridines