Metal center-based emission, luminescent

In complexes of the quinoline based ligands we saw room-temperature emission which was weak or absent and could be related to unfavorable steric factors. Most likely [Ru(dpt)2]2+ is non-luminescent for the same reason. Kirchhoff et al.258) have argued that steric repulsions may cause a 3MC state to lie at lower energy than the 3CT state so that no CT emission occurs. A metal centered state should be more photoactive and [Ru(dpt)2]2+ does indeed undergo photolysis in the presence of nucleophiles. The photolysis product has been formulated as containing a bidentate dpt ligand. 

The copper(I) complex Cu(dmp)2 (dmp = 2,9-dimethyl-l,10-phenanthroline) displays MLCT luminescence in ambient temperature CH2CI2 solutions [85]. This emission has been shown to be quenched by various Lewis bases (B), and the mechanism proposed is addition of B to the MLCT state at the metal center to give an exciplex which decays rapidly (Eq. 6.39). The validity of this mechanism was tested by comparing, in the presence and absence of Lewis base quenchers, the pressure effects on the emission lifetimes of Cu(dmp)2 vvith those on the emission lifetimes of the bulkier 2,9-diphenyl-phen analog Cu(dpp) [86]. The lattice ions should not be as susceptible to reaction of the copper center with B. For both ions, emission quantum yields are small (<10 ) at ambient T and unimolecular photoreactions are not observed, so the pressure sensitivity of x reflects non-radiative deactivation mechanisms. 

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