A compound of formula (I), ##STR00001## where x is 3, 2 or 1, y is 0 or 1, n.sup.1 and n.sup.2, which may be the same or different, are 0 or 1 to 3, X represents a divalent mono- or poly-aromatic and/or heteroaromatic moiety, the or each Y, which may be the same or different if x is 1, represents hydrogen or an optionally substituted hydrocarbon group, Z represents an aromatic group, or an inherently at least partly conjugated dendritic molecular structure comprising one or more aromatic and/or heteroaromatic groups and, optionally, alkenylene groups, connected to each other either directly or via a carbon atom of an alkenylene group, if present, to a ring carbon atom of an (hetero) aromatic group to which more than one at least partly conjugated dendritic chain is attached, said molecular structure being connected to the remainder of the molecule via a ring carbon atom, one or more of the (hetero) aromatic rings of the dendrimers optionally being substituted, Z and/or the remainder of the molecule, excluding any groups Y, being luminescent, with the proviso that when Z represents an aromatic group y must be 1.