| abstract |
Squarylium compounds of formula (I) (in which Q?1 and Q2¿ are each a chromophoric group having an aromatic unsaturated system conjugated with the squarylium ring and such that in the compounds of formulae Q1CH2R?1 and Q2CH¿2R2 the methylene hydrogens are active hydrogen; R?1 and R2¿ are each independently a hydrogen atom or an aliphatic or cycloaliphatic group; and Φ is a group of the formula -NR3R4 or of the formula -CR5R6R7, wherein: R?3 and R4¿ are each independently a hydrogen atom, or an acyl, aliphatic, cycloaliphatic, aromatic or heterocyclic group, subject to the proviso that one of R?3 and R4¿ may be an amino, substituted amino group, or organosulfonyl group, or R?3 and R4¿ together with the intervening nitrogen atom form a nitrogenous heterocyclic ring; and R?5, R6 and R7¿ are each independently a hydrogen atom, or an acyl, aliphatic, cycloaliphatic, aromatic or heterocyclic group, or an electron-withdrawing group able to lower the electron density at the carbon atom to which it is attached) are useful as near infrared absorbers. The presence of the Φ group on the squarylium ring enables minor changes in absorption wavelength to be achieved by modifications of this group, and also allows functional groups to be incorporated into the dye without changing the chromophoric groups. |