A process for printing an image on a substrate comprising applying thereto by means of an ink jet printer an ink comprising a compound of Formula (1): ##STR00001## wherein one of A and B is an optionally substituted heteroaryl group containing a ring sulphur atom and the other is an optionally substituted aryl or heteroaryl group and R.sup.1, X and Y are as specified. Also claimed are compounds of Formula (1) and various compositions containing the same.