Abstract The dimesitylboryl group is a new auxochrome. This group was evaluated by comparison of 4-[p-dimesitylborylphenylazo]-1-naphthol (III) with 4-[p-nitrophenylazo]-1- naphthol (IV) and of the substituted N-[5-hydroxy-8-(4-dimesitylborylphenylazo) naphthyl-1, 3-benzenedisulfonamide (VIIIa) with N-[5-hydroxy-8-(4-nitrophenylazo) naphthyl]-1, 3- benzenedisulfonamide (VIIIb). The syntheses of 5-hydroxy-8-(4-dimesitylborylphenylazo)- ...