The use of fluorene in the photorelease of nitric oxide from Ru(terpyridine)(NO) complexes by one- or two-photon absorption

The use of fluorene (2,2′-methylenebiphenyl) as a donating substituent for the release of nitric oxide (NO) from ruthenium nitrosyl (Ru-NO) complexes is reviewed. Fluorene is a well-known organic fragment in the design of efficient chromophores in two-photon absorption (TPA), a technic that should lead to promising therapeutic application of NO delivery. After a brief introduction on the origin of TPA in molecules, the design of fluorene-based polypyridine ligand is described. The different fluorenylbipyridine and mostly fluorenylterpyridine-based Ru-NO complexes reported in the literature are presented. In all these compounds, the fluorene units act as electron donor towards the withdrawing RuNO fragment. Finally, the possibility of using fluorene as a fluorescent antenna is envisioned and new perspectives are drawn. • Nitric oxide (NO, labelled molecule of the year by the journal Nature, in 1992) possesses numerous biological applications, • Ruthenium nitrosyl (Ru-NO) complexes are one of the most promising molecules capable to photo-release NO locally and quantitatively, • Once π -conjugated to fluorene, the Ru-NO complexes possess significant two-photon absorption characters. • The design of bi- and tri-metallic species leads to molecular units with unusually large TPA response.