NEW FLUORAN LEUCO DYES HAVING A PHENYLENEDIAMINE MOIETY AT THE 6-POSITION OF THE XANTHENE RING

New fluoran leuco dyes incorporating a p-(N,N-dibutylamino)phenylamino moiety at the 6-position of 2,3-dimethylxanthene (1) and of 2-chloro- 3-methylxanthene (2) have been synthesized. The spectral characteristi cs of these compounds were quite different from those of conventional flouran dyes; remarkably broad absorption bands in the range ca. 500-8 50 nm (lambda(max): 608 nm for 1, 645 nm for 2) were observed in m-cre sol as a result of yielding zwitterions of 1 and 2. Coloured anions of these compounds were also formed in a basic methanol solution, The mo lecular structures of the colourless lactones and the coloured zwitter ions were identified by C-13 NMR spectroscopy. The new fluorans report ed herein are promising compounds as a basic skeleton of new functiona l leuco dyes because of their unique spectral characteristics and colo ur properties in both acidic and basic media. (C) 1997 Elsevier Scienc e Ltd.