A ferrocenyl compound having the general formula (I) : (I) Het is a substituted or unsubstituted heterocyclic moiety. L1, L2 and L3 are each a linker independently selected from alkylene, alkyleneoxy, alkyleneoxyalkylene, alkylenecarbonyl, alkyleneoxycarbonyl, alkyleneamido, alkyleneoxyamido, alkenylene, alkenyleneoxy, alkenylenecarbonyl, alkenyleneamido, alkynylene, alkynyleneoxy, alkynylenecarbonyl and alkynyleneamido, all of which may be straight chain or branched, substituted or unsubstituted. R1 and R2 are each independently selected from H, substituted or unsubstituted alkyl carbonyl, substituted or unsubstituted aryl carbonyl, substituted or unsubstituted phosphate, substituted or unsubstituted phosphonate and substituted or unsubstituted phosphoramidate. M and n are each 0 or 1 and m + n ≠0.1
