New Near Infrared Absorbing Metal Complex Dyes: Synthesis and Metallochromic Properties of Two Isomeric Ligands, 2-(Dimethylamino)naphtho {[1,2-g] and [2, 1-g]} quinoline-7,12-diones

The Diels–Alder reaction of 5,8-quinolinedione with p-(dimethylamino)styrenes gave new two kinds of isomeric dyes, 2-(dimethylamino)naphtho[1,2-g]quinoline-7,12-diones and 2-(dimethylamino)naphtho[2,1-g]quinoline-7,12-diones, which showed quite different metallochromic behaviors. Upon addition of metal salts, one of the two isomers showed drastic spectral changes to have an intense absorption band in near infrared region. The color–structure relations were investigated.