Extension of conjugated double bond system at 2′- and/or 6′-positions makes it possible for fluoran compounds to have an absorption in the near infrared region up to 1200 nm. These include 2′-anilino-6-(4-anilinoanilino)- 3′-methylfluoran (62),63 6′-[4-(4-anilinoanilino)anilino]-2′-chloro-
3′-methylfluoran (63),7 6′-[4-(4-dimethylaminoanilino)anilino]-2′-methylflu-
(62) (63) |
oran (64),64 and 6′-diethylamino-2′-[4-(4-dimethylaminoanilino)anilino]-3′- methylfluoran (65).65