Modernity in Ancient Times: Copper Silicate Pigments from Historical Significance to Modern Applications

Egyptian blue is considered the first synthetic pigment, dating back to the 3rd millennium BC¹. It is a layered calcium copper silicate material with the chemical composition CaCuSi₄O₁₀. Later, a related family of these layered silicates were discovered— Han blue (BaCuSi₄O₁₀), and Han Purple (BaCuSi₂O₆)². The layered silicates EB, HB, and HP are known as historic pigments, but they also possess novel optoelectronic properties with strong potential for fundamental research and technology.



These pigments possess a unique photophysical property– they are photoluminescent in the near infrared region (NIR) of the electromagnetic spectrum³. That is, when excited by visible light, electrons on the atoms within the crystal lattice of these materials absorb energy, then relax down to their ground state and emit photons of longer wavelength, in the NIR region. For certain applications, the NIR region of the electromagnetic spectrum has advantages over other wavelength ranges; namely, it is known as the biological window, or the tissue transparency window. Such wavelengths from 760 to 2340 nm show deep penetration through tissue and blood, therefore imaging using NIR light can resolve structures deep within biological tissues⁴. Since copper silicate materials like EB, HB, and HP fluoresce in the NIR region, they can act as efficient NIR fluorophores for biophotonics applications. With high quantum yield, long fluorescent times, and virtually zero photobleaching, these materials have recently shown potential as NIR fluorophores, in the same category as single walled carbon nanotubes (SWCNTs), indocyanine green dyes (ICG), quantum dots, and other inorganic nanoparticles⁴.

This seminar will cover the synthesis, characterization, and modern applications of these ancient materials. EB, HB and HP have been used in various applications including smart inks, energy storage, bioimaging, phototherapy, and more developments point to how these interesting materials may help shape the technological future.

References:

1. Berke, H. The Invention of Blue and Purple Pigments in Ancient Times. Chem. Soc. Rev. 2007, 36 (1), 15–30.

2. Berke, H. Chemistry in Ancient Times: The Development of Blue and Purple Pigments. Angewandte Chemie International Edition. 2002, 41 (14), 1433-7851.

3. Selvaggio, G.; Herrmann, N.; Hill, B.; Dervişoğlu, R.; Jung, S.; Weitzel, M.; Dinarvand, M.; Stalke, D.; Andreas, L.; Kruss, S. Covalently Functionalized Egyptian Blue Nanosheets for near-Infrared Bioimaging. ACS Applied Bio Materials 2022, 6 (1), 309–317.

4. Selvaggio, G.; Kruss, S. Preparation, Properties and Applications of near-Infrared Fluorescent Silicate Nanosheets. Nanoscale 2022, 14 (27), 9553–9575.