Reductive alkylation of aminofluorans: A simple route to intrinsically thermochromic fluorans

• Synthesis of novel hydroxyarylalkylaminofluorans by a reductive alkylation strategy.
• The fluorans exhibit intrinsic thermochromism without the need of an acidic colour developer.
• A hydroxybenzoylamino substituted fluoran was synthesised and exhibited intrinsic thermochromism.

The reductive alkylation of fluoran green base with hydroxybenzaldehydes gave novel fluorans that exhibited thermochromism, reversibly changing colour from very pale pink to deep green, in methyl stearate and in microcapsules containing methyl palmitate/isopropyl palmitate without the need of an added phenolic colour developer. Acylation of fluoran green base with O-acetylsalicyloyl chloride and subsequent cleavage of the acetyl group gave a new colour former bearing an o-hydroxybenzoyl moiety which also exhibited thermochromism, reversibly changing from colourless to red.

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