Metal phthalocyanines (MPs) are known for their strong optical properties and stability. They are commonly used as pigments and dyes, but in recent years they have also shown promise for a wide variety of other applications, including photovoltaic devices and optical limiting materials. These optical and electronic properties can be further improved by creating nanocrystals of MPs.

Takeshi Higuchi, Hiroshi Yabu, and colleagues, Tohoku University, Japan, have developed a method to control the growth of MP crystals so that their sizes remain in the nanoregime. By irradiating micelles loaded with MP precursors with UV light (“nanoreactors”), they were able to create copper phthalocyanine crystals with diameters of approximately 170 nm.

These crystals absorbed strongly from 500 to 800 nm while remaining transparent at other wavelengths, giving their suspensions a beautiful blue color. Compared with microcrystals of the same material prepared by conventional methods, these nanocrystals exhibited decreased light scattering and increased transparency.

The method could also be extended to zinc phthalocyanines, suggesting that it could be used for a variety of other metals.

• One-Pot UV-Assisted Synthesis of Metal Phthalocyanine Nanocrystals,
  Yuta Saito, Takeshi Higuchi, Hidekazu Sugimori, Hiroshi Yabu,
  ChemNanoMat 2015.
  DOI: 10.1002/cnma.201500017