The invention relates to a cross-linking monomer having the structure Q-(L)n-P-(L′)m;-Q′, where Q and Q′ are polymerisable units, L and L′ are linkers providing direct or indirect electronic communication between Q and P and between P and Q′, and P is an electrofunctional unit, and also to polymers prepared from such monomers. Q for example may be a heteroaromatic ring such as thiophene, furan and pyrrole. The electrofunctional group may be, for example, porphyrin, substituted porphyrin, phthalocyanine or substituted phthalocyanine. The invention also relates to an electrofunctional material including a base material and a cross-linked polymer such as described.