Enhancing solar thermal storage properties of azobenzenes with conductive polymer: Electropolymerization of carbazole containing photoactive cyanoazobenzene derivative

Solar thermal fuels (STFs) have recently drawn attention as a promising strategy for utilization of solar energy that is a clean and renewable source. Especially solid state solar thermal fuels have high potential to be used in thermal applications. However, up to date, it is seen that the solar thermal storage capacity in the polymeric state is lower than in the corresponding monomers. Herein, for the first time, photoactive azobenzene and electroactive carbazole containing monomer (Cz-AzoCN) was designed and thermal storage properties of the monomer and the corresponding polymer obtained by electropolymerization were investigated. This study showed that polycarbazoles containing azobenzene pendant groups can be an effective thermal storage platform due to their easy functionality, high light absorption and rigid conjugated chain structure resembling the structure of rigid templates decorated with closely packed photochromic units. Additionally, electropolymerization is an easy and rapid method for polymer synthesis, producing polymer in the form of film that is ready for irradiation. The gravimetric energy storage density of p(Cz-AzoCN) was calculated as 145.12 j g  1 which was 128 % higher than that of monomer. This is due to boosted light harvesting of conjugated polycarbazole backbone as an organic photosensitizer that providing effective solar thermal storage.