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Organic nanocrystals of 1,3,5-triphenyl-2-pyrazoline (TPP) with a series of sizes were synthesized by reprecipitation method. The luminescence quantum efficiency of TPP nanocrystals increases from 24.2% for the nanocrystals with an average size of 300 nm to 34.6% for those with an average size of 20 nm. Surface capping by polyvinyl pyrrolidone (PVP) will improve the quantum efficiency of TPP nanocrystals. The size-dependence and capping-induced variation of the luminescence quantum efficiency was elucidated in viewpoint of aggregation quenching and the equilibrium between the TPP monomers and the aggregates in TPP nanocrystals.

Photochromic polymolybdate-citric acid composite films were fabricated. It was found that after UV irradiation the composite films with different molar ratios of organic/inorganic components exhibited different colors. The UV-irradiated films showed dark blue, dark khaki and light sea green colors when the ratios were 1.0, 0.3 and 0.2, respectively. It was identified by Raman spectra that the polymolybdate species formed in the composite films after UV irradiation were sensitive to the ratios of the organic/inorganic components, thus resulting in the different colors of irradiated films. Citric acid played an important role during the photochromic process. Under UV light irradiation, it served as hole scavenger that suppresses the recombination of photogenerated electrons and holes to make the polymolybdates show UV light photochromism.