The design and development of new thermally stable infra-red active photochromic compounds

E-beta-dicyanomethylene-4-alkylidene-3-[1-(substituted-3-furyl or-3-thienyl)ethylidene)tetrahydrofuran-2-ones, (prepared by base-catalysed condensation of the corresponding E-fulgides with malononitrile, followed by cyclisation with acetyl chloride) undergo base-catalysed cyclisation to photochromic 3-alkylidene-6-amino-7-cyano(substituted-3-furyl or 3-thienyl)-2,3-dihydrobenzofuranones, which photocyclise to compounds having long wavelength absorption band maxima at ca. 750 nm. Charge transfer characteristics in the photochromes are essential for retention of aromatic character in the annelated benzene ring.