A naphthalocyanine dye of formula (I) is provided: ##STR00001## wherein M is a metal group or is absent; R.sup.1 and R.sup.2 are independently selected from hydrogen or C.sub.1-12 alkoxy; X is selected from O, S or --NH--; Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, Ar.sup.5, Ar.sup.6, Ar.sup.7 and Ar.sup.8 are selected from phenyl, naphthyl, pyridyl, furanyl, pyrollyl, thiophenyl, each of Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, Ar.sup.5, Ar.sup.6, Ar.sup.7 and Ar.sup.8 being optionally substituted with 1, 2, 3, 4 or 5 groups, the or each group being independently selected from C.sub.1-12 alkyl, C.sub.1-12 alkoxy, C.sub.1-12 arylalkyl, C.sub.1-12 arylalkoxy, --(OCH.sub.2CH.sub.2).sub.dOR.sup.d, cyano, halogen, amino, hydroxyl, thiol, --SR.sup.v, --NR.sup.uR.sup.v, nitro, phenyl, phenoxy, --CO.sub.2R.sup.v, --C(O)R.sup.v, --OCOR.sup.v, --SO.sub.2R.sup.v, --OSO.sub.2R.sup.v, --NHC(O)R.sup.v, --CONR.sup.uR.sup.v, --CONR.sup.uR.sup.v, sulfonic acid, sulfonic acid salt and sulfonamide; d is an integer from 2 to 5000; R.sup.d is H, C.sub.1-8 alkyl or C(O)C.sub.1-8 alkyl; and R.sup.u and R.sup.v are independently selected from hydrogen, C.sub.1-12 alkyl, phenyl or phenyl-C.sub.1-8 alkyl.