Near-infrared absorbing methine dyes based on dicyanovinyl derivatives of indane-1,3-dione

The synthesis, colour, and constitution of methine dyes formed by condensation of benzaldehydes and nitrosobenzenes with dicyanovinyl analogues of indane-1,3-dione have been investigated. 3-Dicyanovinylindan-1-one (3) and 1,3-bisdicyanovinylindane (5) give magenta (λmax.ca. 560 nm) and blue (λmax.ca. 600 nm) dyes respectively with 4-dialkylaminobenzaldehydes. Aza analogues formed from (3) and (5) and 4-dialkylaminonitrosobenzenes are significantly more bathchromic, 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.