Copper(I) complexes of 1,10-phenanthroline–oligophenylenevinylene conjugates
Copper(I) complexes obtained from 2,9-diphenyl-1,10-phenanthroline derivatives substituted with an oligophenylenevinylene (OPV) unit have been prepared. Very strong intramolecular quenching of the lowest OPV excited state by the copper(I) complex has been evidenced in these multicomponent systems. The mechanism of the photoinduced process depends on the length of the conjugated OPV backbone. Upon irradiation of the OPV unit, quantitative sensitization of the Cu(I) complex has been evidenced for the system substituted with trimeric OPV units, but not for those with tetrameric OPV units. Therefore, energy transfer is the sole quenching mechanism for the former complex, whereas electron transfer might play a role in the latter case. This different behaviour is ascribed to the slightly increased electron-accepting character of the OPV tetrameric unit when compared to the corresponding trimer. As far as excited state deactivation in the copper(I) complex is concerned, the hybrid compounds exhibit the characteristic luminescence band attributable to the deactivation of low-lying metal-to-ligand charge transfer (MLCT) excited state(s). As shown by the comparison with a model copper(I) complex, the OPV units have no influence on the MLCT excited state(s) deactivation at room temperature in fluid solutions. In contrast, they are capable of acting as “hooks” when the measurements are performed at low temperature in a rigid matrix, thus reducing the excited state distortion of the copper(I) complex. As a result, at 77 K the MLCT emission spectral shapes and band maxima of the hybrid compounds are no longer identical to those of the corresponding model complex.