Chromogenic fluorene-9-spiro-lactones have the formula:
where R 1 , R 2 , R 3 , R 4 and E have defined meaning. The compounds can be made by diazotizing and then effecting a ring closing reaction on the corresponding precursor primary amino-substituted phthalide, furopyridine or furopyrazine. Compounds where E is a group of the formula
and R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each C 1 -C 4 alkyl groups are preferred. The compounds are chromogenic and can be used in pressure and/or heat sensitive record material. They give lightfast blue to green colours when reacted with electron accepting co-reactants. The coloured forms exhibit marked absorption in the near infrared making them particularly useful in OCR detection systems.