A compound of Formula (I) D-S1-A-S2—B1,  Formula (I) wherein: A represents a conjugated chain of from 1 to 20 aromatic moieties independently selected from the group consisting of aromatic moieties, heteroaromatic moieties and E moieties, provided that A includes at least one E moiety, wherein E is selected from the group consisting of: E1 being a dibenzo[d,b]silole moiety of the structure: E2 being a moiety of the structure: and E3 being a moiety of the structure: wherein E is connected in the conjugated chain of A and optionally to S1 or to S2 through covalent bonds at Y and Z; wherein each R is independently selected from the group consisting of straight chain or branched C1-C20 alkyl and C2-C20 alkenyl, optionally wherein from 1 to 5 CH2 groups are each replaced by an oxygen, provided that no acetal, ketal, peroxide or vinyl ether is present in the R group, and optionally wherein each H bonded to a C in each R group may independently be replaced by a halogen; wherein the X moieties are the same and are selected from the group consisting of hydrogen, straight chain or branched C1-C8 alkyl, straight chain or branched C1-C8 alkoxyl and a halogen, wherein each E moiety may have the same or different X moieties, wherein W is either an oxygen or sulfur atom, D represents a moiety having one or more cross-linkable functionalities, S1 and S2 are flexible linker groups; and B1 represents a moiety having one or more cross-linkable functionalities or a hydrogen atom, with the proviso that when B1 represents a hydrogen atom, D represents a moiety having at least two cross-linkable functionalities.