We synthesized new [Cu(NN)(2)](+)-type complexes where NN = 2-5 and denotes a 2,9-disubstituted-1,10-phenanthroline ligand (related complexes of 1 and 6 ligands are used for reference purposes). For 2, 3, and 4 the ligand substituents are long alkyl-type fragments, whereas in 5 a phenyl ring is directly attached to the chelating unit. At 298 K the four complexes display relatively intense metal-to-ligand-charge-transfer (MLCT) emission bands with maxima around 720 nm, Phi(em) approximately 1 x 10(-)(3) and tau > 100 ns in deaerated CH(2)Cl(2). The emission behavior at 77 K in a CH(2)Cl(2)/MeOH matrix is quite different for complexes of alkyl- (2-4) versus phenyl-substituted (5) ligands. The former exhibit very intense emission bands centered around 642 nm and hypsochromically shifted with respect to 298 K, whereas the luminescence band of [Cu(5)(2)](+) is faint and shifted toward the infrared side. These results prompted us to study in detail the temperature dependence of luminescence properties of [Cu(2)(2)](+) and [Cu(5)(2)](+) in the 300-96 K range. For both complexes the excited state lifetimes increase monotonically by decreasing temperatures, and the trend is well described by an Arrhenius-type treatment involving two equilibrated MLCT excited levels. The emission bands show a similar behavior for the two compounds (intensity decrease and red-shift) only in the 300-120 K range, when the solvent is fluid. In the frozen regime (T

The rhenium(I) and ruthenium(II) complexes of a fullerene‐substituted bipyridine ligand have been prepared. Electrochemical studies indicate that some ground state electronic interaction between the fullerene subunit and the metal‐complexed moiety are present in the ReI but not the RuII complex. The photophysical properties have been investigated by steady‐state and time‐resolved UV/Vis‐NIR luminescence spectroscopy and nanosecond laser flash photolysis in CH2Cl2 solution, and compared to those of the corresponding model compounds. Excitation of the methanofullerene moiety in the dyads does not lead to excited state intercomponent interactions. Instead, excitation of the metal‐complexed unit shows that the lowest triplet metal‐to‐ligand‐charge‐transfer excited state (3MLCT) centered on the ReI‐ or RuII‐type unit is quenched with a rate constant of about 2.5×108 s−1. The quenching is attributed to an electron‐transfer (ElT) process leading to the reduction of the carbon sphere, as determined by luminescence spectroscopy for the RuII dyad. Experimental detection of electron transfer in the ReI dyad is prevented due to the unfavorable absorption of the metal‐complexed moiety relative to the fullerene unit. However, it can be postulated on the basis of energetic/kinetic arguments and by comparison with the RuII‐type array. The primary ElT process is followed by charge‐recombination to give the lowest‐lying fullerene triplet excited state (3C60) with quantitative yield, as determined by sensitized singlet oxygen luminescence experiments. Direct 3MLCT→3C60 triplet–triplet energy‐transfer (EnT) does not successfully compete with ElT since it is highly exoergonic and located in the Marcus inverted region. The quantum yield of singlet oxygen sensitization (ΦΔ) of the ReI‐based dyad is found to be lower (0.80) than for the corresponding RuII derivative (1.0). This is likely to be the consequence of different conformational structures for the two dyads, rather than a different yield of 3C60 formation.

Transient absorption spectrometry of Cu(I)-phenanthrolines in CH2Cl2 reveals ligand-independent dynamic processes lasting 15 ps, which are associated with the peculiar structural rearrangements occurring for this class of compounds upon photoexcitation.