Quinoid Polynuclear Aromatics
This final group of dyes is based mainly on derivatives of 1,4-Naphthoquinones. These compounds have long been used as basic visible dyes and are renowned for the wide range of colours possible with amino substitution. Dyes such as the derivative shown here are usable as nIR absorbers, but have the disadvantage of poor thermal and chemical stabilities. This increases the difficulty and therefore the cost of the coating process in disc manufacture as well as jeopordising the data retention performance of such discs.
The alternative is to use phenothiazine or phenoselenazine derivaties as below. These are easily coated onto discs and absorb between 750 and 850nm.