Benzpyrylium dyes, and processes for their preparation and use

摘要

4-[3-(benz[b]pyran-4-ylidene)prop-1-enyl]benz[b]pyrylium, 4-[5- (4H- benz[b]pyran-4-ylidene)penta-1,3-dienyl]benz[b]pyrylium and 4-[7-(4H- benz[b]pyran-4-ylidene)hepta-1,3,5-trienyl]benz[b]pyrylium dyes, wherein at least one of the benzpyrylium nuclei carries at its 2-position a substituent in which a non-aromatic carbon atom is bonded directly to the benzpyrylium nucleus, subject to the proviso that if the or each 2- substituent contains an aromatic nucleus, this aromatic nucleus is not conjugated with the benzpyrylium nucleus, are useful as visible and near infra-red absorbers, having high extinction coefficients and a reduced tendency to develop absorptions at shorter wavelengths when dispersed in polymeric media.