Terpyridine ligands of the type Fc'-X-tpy (Fc'=ferrocenyl or octamethylferrocenyl, X=rigid spacer, tpy'=4'-substituted 2,2':6',2''-terpyridine) were prepared, crystallographically characterised and used for the synthesis of di- and trinuclear bis(terpyridine) complexes of RuII, FeII and ZnII. Donor-sensitiser dyads and triads based on RuII were thoroughly investigated by (spectro)electrochemistry, UV/Vis, transient absorption and luminescence spectroscopy, and an energy level scheme was derived on the basis of the data collected. Intramolecular quenching of the photoexcited RuII complexes by the redox-active Fc' groups can occur reductively and by energy transfer. Both the redox potential of the donor Fc' and the nature of the spacer X have a decisive influence on excited-state lifetimes and emission properties of the complexes. Some of the compounds show room-temperature luminescence, which is unprecedented for ferrocenyl-functionalised compounds of this kind.

Using product analysis and time-resolved laser flash photolysis techniques, the photochemistry at A, , , X 250 and 310 nm (exc = excitation) of l-(p-R-phenyl)-2-(2,2'-biphenyldiyl)vinyl halides (R = H, Me, MeO) in methanol and acetonitrile at room temperature was studied. The title compounds undergo photoheterolysis and photohomolysis to give vinyl cations =C+-(carbenium ions) and vinyl radicals =c'--. The cation: radical ratio increases with electron-donating strength of the substituent R, H < Me < MeO, and with anionic leaving group power of the halide, F-< C1-< Br-< I-, indicating that the cleavage of the C-X bond to yield cation and halide anion proceeds, in the rate-determining step, by heterolysis and not by homolysis followed by electron transfer in the radical pair. The cation:radical ratio is solvent dependent: e.g., for the vinyl bromide with R = M e 0 and with A, , , = 308 nm, in CH2Clz as solvent, only radical is observed, in comparison with only cation in the much more polar solvent acetonitrile. In acetonitrile-methanol mixtures, the absolute yields of both cation and radical go through a maximum as the methanol content is increased, however, the cation:radical ratio decreases continuously with increasing [MeOH]. For a particular R, the quantum yield for C-X bond cleavage is higher at ~2 5 0 than at ~3 1 0 nm. Also, the cation:radical ratio is wavelength-dependent: at A, , , x 310 nm there is relatively more heterolysis than at A, , , z 250 nm. Rate constants for reaction of the cations with nucleophiles were determined in acetonitrile. Those for reaction of the cation with R = M e 0 (lifetime in acetonitrile 7 ps) with anionic nucleophiles such as the halides are at the diffusion limit in this solvent, x 2 x 1O'O M-' s-l, whereas those for reaction with water, alcohols, and cyclic ethers are of the order 105-106 M-' s-l. The less stabilized cation (R = Me) reacts with alcohols faster by the factor ~1 0 0 , and it decays in acetonitrile e l 0 0 times more rapidly. Also, l-(p-R-phenyl)-2-dimethylvinyl bromides (R = H, Me, MeO) were photolyzed in acetonitrile. In the case of R = MeO, the cation p-CH30-c&-c+=CMe2 was seen (lifetime 770 ns), and its reactivity with alcohols (k values of 106-107 M-' s-') and halides (k values of 1O' O M-' s-l) was determined. The vinyl radicals =c'-react with 0 2 to yield vinylperoxyl radicals =C-Oi which have absorption maxima at ~3 9 0 nm.