Quinacridone visible spectra

Figure 18-1 Visible spectra of quinacridone — absorption spectrum of quinacridone in hexamethylphosphoramide solution ...

It is noteworthy that the visible spectrum of quinacridone in concentrated sulfuric add is remarkably similar to the corresponding spectrum of pentacene in trichlorobenzene solution but shows a strong bathochromic shift relative to the visible spectrum of quinacridone in N,N-dimethylformamide (DMF) solution (Figure 18.2). This is to be expected if the degree of aromatic character of the molecule is increased on protonation. The spectrum is best interpreted on the basis of the di-cation 32 where protonation has taken place on the oxygens rather than the nitrogen atoms. This is... 

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