Ground and excited state communication within a ruthenium containing benzimidazole metallopolymer

Abstract

Emission spectroscopy and electrochemistry has been used to probe the electronic communication between adjacent metal centres and the conjugated backbone within a family of imidazole based metallopolymers, [Ru(bpy)₂(PPyBBIM)_n]²⁺, in the ground and excited states, bpy is 2,2′-bipyridyl, PPyBBIM is poly[2-(2-pyridyl)-bibenzimidazole] and n = 3, 10 or 20. Electronic communication in the excited state is not efficient and upon optical excitation dual emission is observed, i.e., both the polymer backbone and the metal centres emit. Coupling the ruthenium moiety to the imidazole backbone results in a red shift of approximately 50 nm in the emission spectrum. Luminescent lifetimes of up to 120 ns were also recorded. Cyclic voltammetry was also utilized to illustrate the distance dependence of the electron hopping rates between adjacent metal centres with ground state communication reduced by up to an order of magnitude compared to previously reported results when the metal to backbone ratio was not altered. D_CT and D_e values of up to 3.96 × 10⁻¹⁰ and 5.32 × 10⁻¹⁰ cm² S⁻¹ were observed with corresponding conductivity values of up to 2.34 × 10⁻⁸ S cm⁻¹.