Polydiacetylene microcrystals

Polydiacetylene Microcrystals for Third-Order Nonlinear Optics... 

Figure 4 (A) A pre-resonant near-field Raman spectrum of a polydiacetylene microcrystal taken using 633 nm excitation, approximately 150 nm aperture and a 60 s exposure. (B) A 3 pm X 2 pm near-field Raman image of the polydiacetylene microcrystallites. A Raman spectra as in (A) is obtained at every point in the image, and the intensity of any peak may be chosen to produce a grey scale image, in this case the 1485 cm- feature. The vibration mode responsible for this line is shown.

Nakanishi H, Katagi H (1998) Microcrystals of polydiacetylene derivatives and their linear and nonlinear optical properties. Supramol Sci 5 289-295... 

Microcrystals of some diacetylenes, prepared by the reprecipitation method, have been studied as dispersions in liquid media. Interesting behavior has been observed in the solid-state polymerization of diacetylene monomers and with the optical properties of polydiacetylene (PDA) microcrystals. First, the polymerization perfectly proceeded from one end to the other end of the diacetylene microcrystals. Next, the excitonic absorption peak position was found to shift to higher energy side with decreasing size of the PDA microcrystals. The size effect was observed even for crystals as large as 100 nm or more in contrast to conventional quantum effect of inorganic semiconductors where size effect is observed only for microciystals of less than about 10 nm size. In addition, since the microcrystal dispersions in water have low optical loss, the c tical Kerr shutter response of PDA microciystals could be measured, and the non-resonant value was estimated to be on the order of 10 to 10" esu in very low concentrations (ca. 10 M). 

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