A compound of Formula D-S 1 -A-S 2 -B 1, wherein: A represents a conjugated chain of from 1 to 30 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: E 1 being a dibenzo[d,b]silole moiety of the structure: E 2 being a moiety of the structure: and E 3 being a moiety of the structure: wherein E is connected in the conjugated chain of A, and optionally to S 1 or to S 2, through covalent bonds at Y and Z; wherein each R is independently selected from the group consisting of straight chain or branched C 4 -C 20 alkyl and C 4 -C 20 alkenyl, optionally wherein from 1 to 5 CH 2 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 C 1- C 8 alkyl, straight chain or branched C 1 -C 8 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, S 1 and S 2 are flexible linker groups; and B 1 represents a moiety having one or more cross-linkable functionalities or a hydrogen atom, with the proviso that when B 1 represents a hydrogen atom, D represents a moiety having at least two cross-linkable functionalities, wherein each flexible linker group S 1 and S 2 are independently selected from straight chain or branched C 5 -C 14 alkyl groups, optionally wherein 1 to 5 methylene groups are substituted for an oxygen atom provided that no acetal, ketal or peroxide is present in said flexible linker group. A represents a conjugated chain of from 1 to 30 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: E 1 being a dibenzo[d,b]silole moiety of the structure: E 2 being a moiety of the structure: and E 3 being a moiety of the structure: wherein E is connected in the conjugated chain of A, and optionally to S 1 or to S 2, through covalent bonds at Y and Z; wherein each R is independently selected from the group consisting of straight chain or branched C 4 -C 20 alkyl and C 4 -C 20 alkenyl, optionally wherein from 1 to 5 CH 2 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 C 1- C 8 alkyl, straight chain or branched C 1 -C 8 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, S 1 and S 2 are flexible linker groups; and B 1 represents a moiety having one or more cross-linkable functionalities or a hydrogen atom, with the proviso that when B 1 represents a hydrogen atom, D represents a moiety having at least two cross-linkable functionalities, wherein each flexible linker group S 1 and S 2 are independently selected from straight chain or branched C 5 -C 14 alkyl groups, optionally wherein 1 to 5 methylene groups are substituted for an oxygen atom provided that no acetal, ketal or peroxide is present in said flexible linker group.