Letters

摘要

I enjoyed Jane Callender's article on indigo (Journal 231, 2009) but would like to point out a misconception. In her article, Jane said 'Astonishingly, the molecular structure of natural and synthetic indigo is the same'. It is not astonishing, it is a necessity. The colour that we see is a result of light absorption as electrons move around the molecule (so called resonance). The organic ring structure of indigo (and so many more dyestuffs) allows this resonance to easily take place. The exact resonance pattern (and hence colour) depends on the rings and any molecular groups attached to them.