Fluorescence of Supermolecules, Polymers, and Nanosystems

Abstract

The history of molecular fluorescence is closely associated with the emission from plant extracts. N. Monardes, in his Historia Medicinal (Seville, 1565), was the first to describe the blue opalescence of the water infusion of the wood of a Mexican tree used to treat kidney ailments. The strange optical properties of the wood, known as Lignum nephriticum (kidney wood), were later investigated by Kircher, Grimaldi, Boyle, Newton and many other scientists and naturalists in the ensuing centuries. However, when G.G. Stokes published in 1852 the first correct relationship between light absorption and fluorescence, his observations were based on the emission of quinine sulphate solution, because in Europe the wood of Lignum nephriticum was no longer available and its botanic origin was unknown. An inspection of the works of sixteenth century Spanish missionaries and scholars who compiled information on the Aztec culture, such as Fr. Bernardino de Sahagun and Francisco Hernandez, indicates that pre-Hispanic Indian doctors had already noticed the blue color (fluorescence) of the infusion of coatli, a wood used to treat urinary diseases. Coatli wood was obtained from Eyserhardtia, a tree of the family of Leguminosae, and is the most likely source of the exotic Lignum nephriticum. The wood of Eysenhardtia polystachya contains large quantities of Coatline B, a rare C-glucosyl-α-hydroxydihydrochalcone. This compound gives rise to a fluorescent reaction product, in slightly alkaline water at room temperature, which is responsible for the blue emission of Lignum nephriticum infusion.