Carbazole-Pyridazine copolymers and their rhenium complexes: Effect of the molecular structure on the electronic properties

Two new push–pull copolymers, poly[N-(9-heptadecanyl)carbazole-2,7-diyl-alt-phthalazine- 5,8-diyl] (P1) and poly[N-(9-heptadecanyl)carbazole-2,7-diyl-alt-thieno[3,4-d]pyridazine- 5,7-diyl] (P2), were synthetized by means of a Suzuki polycondensation. The molecular characterization with 1H NMR and MALDI-MS showed enchainment defects in the polymer backbones depending on the synthetic conditions (catalyst and temperature). Both carbazole-carbazole and diazine-diazine homocoupling defects occurred, particularly in the case of P2. For P1, instead, almost homocoupling-free material was obtained. Exploiting the metal coordination capability of the pyridazine ring, corresponding dinuclear rhenium-based metallopolymers, ReP1 and ReP2, were also synthetized. All materials were investigated with experimental techniques (UV–vis spectroscopy, photoluminescence, cyclic voltammetry) and corroborated by theoretical studies (DFT and TD-DFT), including a qualitative evaluation of the effects of backbone defects on the electronic properties of the polymers. They were also tested in organic photovoltaic (OPV) devices. The wide energy gaps (Eg) accompanied with a low absorption coefficient for the band in the visible range reduced the harvesting capability of the copolymers. These drawbacks were partially overcome in the metallopolymers. The low device performance was mainly attributable to the low solubility of the metallopolymers in the organic solvents.