The 4[prime or minute]-(2-fluorenyl)-2,2[prime or minute]:6[prime or minute],2[prime or minute][prime or minute]-terpyridine (FT) ligand and its cis(Cl,Cl)- and trans(Cl,Cl)-[RuII(FT)Cl2(NO)](PF6) complexes have been synthesized. Both isomers were separated by HPLC and fully characterized by 1H and 13C NMR. The X-ray diffraction crystal structures were solved for FT (Pna21 space group, a = 34.960(4), b = 5.9306(7), c = 9.5911(10) A), and trans(Cl,Cl)-[RuII(FT)Cl2(NO)](PF6)[middle dot]MeOH (P[1 with combining macron] space group, a = 10.3340(5), b = 13.0961(6), c = 13.2279(6) A, [small alpha] = 72.680(2), [small beta] = 70.488(2), [gamma] = 67.090(2)[degree]). Photo-release of NO[radical dot] radicals occurs under irradiation at 405 nm, with a quantum yield of 0.31 and 0.10 for cis(Cl,Cl)-[RuII(FT)Cl2(NO)](PF6) and trans(Cl,Cl)-[RuII(FT)Cl2(NO)](PF6), respectively. This significant difference is likely due to the trans effect of Cl-, which favors the photo-release. UV-visible spectroscopy and cyclic voltammetry indicate the formation of ruthenium(iii) species as photoproducts. A density functional theory (DFT) analysis provides a rationale for the understanding of the photo-physical properties, and allows relating the weakening of the Ru-NO bond, and finally the photo-dissociation, to HOMO [rightward arrow] LUMO excitations.