We have developed peptide materials with chromophores that undergo cycloaddition, suitable for terabit optical digital storage in a 5.25 in. disc. The rationale behind this design is that the length and rigidity of the backbone can be adjusted to facilitate the formation of a photodimer without large physical movements of the chromophores on exposure to UV light. Initially strongly absorbing films transmit up to 50% of light on irradiation at dimerizing wavelengths. This property can be utilized to record grey levels. An intensity-dependent transmission behavior has been observed that may enable data to be written and read at the same wavelength. (C) 2004 American Institute of Physics.