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 characteristics of these compounds were quite different from those of conventional flouran dyes; remarkably broad absorption bands in the range ca. 500–850 nm (λmax: 608 nm for 1, 645 nm for 2) were observed in m-cresol as a result of yielding zwitterions of 1 and 2. Coloured anions of these compounds were also formed in a basic methanol solution. The molecular structures of the colourless lactones and the coloured zwitterions were identified by 13C NMR spectroscopy. The new fluorans reported herein are promising compounds as a basic skeleton of new functional leuco dyes because of their unique spectral characteristics and colour properties in both acidic and basic media.