Colour and chromism of conjugated polymers

Abstract Long-chain conjugated polymers are described which have electronic transitions with energies of approximately 2–4 eV. Excitation of these transitions by electromagnetic radiation results in strong absorption bands in the visible region of the spectrum and hence a coloured appearance to the polymer. It is shown that the energy of the excitations, and hence the colour of the polymers, is dependent upon factors such as the length of the polymer chain, the environment in which it is located and the backbone conformation. The absorption spectrum is so sensitive to these and other factors that small changes may lead to chromism, a dramatic change in colour of the polymer. Polymers that exhibit thermochromism, solvatochromism, electrochromism and other colour changes are discussed. The changes in colour are interpreted as arising primarily from changes in the structure of the polymer. The existing and potential technological applications or chromism in conjugated polymers are considered.