Natural Dyes for Photonics Applications

Abstract

Natural dyes are chemical cycles extracted from plants, invertebrates or minerals. From the animal world, one could distinguish those derived from cochineal insect (red), cow urine (Indian yellow), lac insect (red, violet), murex snail (purple) and octopus or cuttlefish (sepia brown). From the plant world, the major ones are extracted from catechu or cutch tree (brown), Cambodge tree resin (dark mustard yellow), Himalayan rubhada root (yellow), indigofera plant (blue), kamala tree (orange–yellow, golden yellow), madder root (red, pink, orange) and pomegranate peel (yellow), among others. In 1856, William Henry Perkin discovered the first synthetic dye ‘Mauve’, which is a basic dye (aniline), while searching for a cure for malaria, indirectly pioneering a new industry of synthetic dyes. This was followed by the design of the second synthetic dye, alizarin (synthetic madder), by Graebe and Liebermann andW.H. Perkin in 1868. The discovery of man-made synthetic dyes in the mid 19th century triggered a long decline in the large-scale market for natural dyes. Synthetic dyes, which could be produced in large quantities, quickly superseded natural dyes for commercial textile production, and unlike natural dyes they were suitable for the synthetic fibres industry. While the usage of natural dyes was/is blooming in the food industry as a colorant and in modern medicine, there is also an obvious growing interest from the photonics community in such natural chemical systems due to their π–π*/conjugated electronic structures. In nonlinear photonics, it was demonstrated that extracts from Hibiscus sabdariffa, commonly known as Roselle, carminic acid of the cochineal scale and saffron exhibit exceptional nonlinear optical (NLO) properties of a prime importance in optics. Yet, as early as the birth stage of lasers, coumarin (C9H6O2), which is found naturally in high concentration in the tonka bean (Dipteryx odorata), was used in dye lasers. As shown in Figure 35.1, coumarin dye is still the basic active medium for many tunable dye laser sources (Duarte and Hillman, 1990; Schafer, 1990).The second sector where natural dyes are attracting a growing interest is the dye solar cells (DSCs) field. Indeed, recent efforts in DSCs are focusing on increasing the solar photo-conversion while lowering the manufacturing costs by using ruthenium (Ru)/osmium (Os) free organic dyes. Owing to their intermolecular π–π* transitions, natural dyes exhibit