We propose that the supercritical fluid crystallization (SCFC) method is one of the most promising techniques for preparing organic microcrystals. In the case of titanylphthalocyanine (TiOPc) and diacetylenes, the size and forms of the resulting microcrystals could be controlled by changing SCFC conditions. In particular, the SCFC method for the microcrystallizaton of phthalocyanines is expected to be useful, replacing the previous acid-pasting method.

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We report a study on the resonant third-order nonlinear optical response of vanadyl-phthalocyanine micro-crystals. The refractive and absorptive contributions to the nonlinear response at several wavelengths across resonance were determined by employing the z-scan technique with a tunable picosecond pulsed laser source. The samples studied were cyclohexane suspensions of vanadium-oxide phthalocyanine micro-crystals 40 nm in diameter. These micro-crystals represent an interesting alternative for the production of solid state samples of good optical quality through relatively simple techniques. Experimental results show that for wavelengths above 610 nm, the sample presents saturation of absorption, while for shorter wavelengths, induced absorption is found. Around 610 nm however, the absorptive contribution to the nonlinearity vanishes while a finite refractive contribution remains. This wavelength region is therefore potentially useful for all-optical switching applications.

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