The synthesis, colour, and constitution of methine dyes formed by condensation of benzaldehydes and nitrosobenzenes with dicyanovinyl analogues of indane-lr3-dione have been investigated. 3-Dicyanovinylindan-1 -one (3) and lr3-bisdicyanovinylindane (5) give magenta (hmax. ca. 560 nm) and blue (Amax, ca. 600 nm) dyes respectively with 4-dialkylaminobenzaldehydes. Aza analogues formed from (3) and ( 5) and 4-dialkylaminonitrosobenzenes are significantly more bathochromic, and the exceptional shift in the case of dyes formed from (5) (ca. 150 nm) permits the synthesis of a new class of dyes absorbing in the near-i.r. region, with absorption maxima in the range 700-850 nm.

The condensation of the benzaldehyde (IIa) with the bisdicyanovinylindane (VI) requires acetic anhydride as solvent.