Synthesis and solid state absorption spectra of some aminonaphthoquinone dyes

The 2,6- and 4,8-bisarylamino-1,5-naphthoquinone derivatives 3b-d and 6a-e were synthesized by the amination of naphthazarin (1) and naphthazarin intermediate (4), respectively. Their chromophoric systems were evaluated by the PPP MO method, and their absorption spectra in solution and the solid state were investigated to evaluate the intermolecular pi-pi interactions of the dye molecules in the solid state. In the case of dyes 3a-d, large Delta lambda values of over 100 nm were obtained, but in 3b-d another absorption maximum at shorter wavelength was also observed. On the other hand, dyes 6c-e showed large Delta lambda values of over 90 nm, but dyes 6a and 6b showed relatively small Delta lambda values of less than 45 nm. The chain length of the alkyl and alkoxy substituents influenced the molecular stacking of the dye in the solid state. Copyright (C) 1996 Elsevier Science Ltd