Luminescence quenching of partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complex in methanol

Metallopolymers in which bis(2,2'-bipyridine)ruthenium(II) complexes are coordinated to imidazolyl residues on partially quaternized poly(1-vinylimidazole) having different degree of quaternization (RuQPIm) were synthesized. The luminescence quenching of the photoexcited RuQPIms with various alkylviologens having different length of alkyl group was investigated in MeOH. In quenching of RuQPIm with methylviologen group (MV2+), the efficiency of quenching decreases with increasing degree of quaternization. This was attributed to the electrostatic repulsion between the MV2+ species and the quaternized imidazolium residue on the polymer backbone and steric hindrance of the alkyl side chain. Furthermore, the efficiency of quenching depends on the length of the alkyl group in viologen. These results suggest that the alkyl side chain on the polymer backbone exerts steric hindrance at low degree of quaternization and van der Waals interaction at high degree of quaternization.