The Nobel Prize in Chemistry 1905 was awarded to Adolf von Baeyer "in recognition of his services in the advancement of organic chemistry and the chemical industry, through his work on organic dyes and hydroaromatic compounds".
 

Inspired by his mentor August Kekulé's pioneering theory, which proposed that you can assign certain atoms to their correct positions within a molecule by virtue of their behaviour in chemical reactions, Baeyer meticulously carried out such reactions to formulate the structures of many compounds. The most important of these was his derivation of the approximate structure of indigo, a beautiful and distinctive blue dye extracted from the plant of the same name for use in textiles and printing. In addition, Baeyer discovered a prominent collection of dyes, the phthaleins, and worked out their chemical composition. Both indigo and phthalein dyes belong to the same group of chemicals, named aromatic on the basis that their carbon atoms form a ring, and Baeyer developed theories to propose how the number of carbon atoms present in rings belonging to a subgroup of these compounds, called hydroaromatic, could explain why certain compounds are more stable than others. Starting from easily available products from the petrochemical industry and even waste products, chemists developed variations of Baeyer's breakthrough experiments to produce synthetic indigo, and eventually almost all the colours of the rainbow.