Thermodynamically stable, highly emissive poly(diphenylacetylene) derivative containing long alkyl side chain without silylene linkage

A PDPA derivative with a long alkyl side chain connected directly onto the backbone (1) was synthesized and compared to a corresponding polymer with a silylene linkage between the side chain and the backbone (2). Polymers 1 and 2 showed similar solubilities: both polymers dissolved well in organic solvents such as toluene, THF, and chloroform but not in polar solvents such as DMF and alcohols. When cast from toluene solutions, smooth and transparent films were readily obtained. Thermogravimetric analysis showed that 1 was more thermally stable than 2 owing to the absence of the relatively weak silylene linkage. Differential scanning calorimetry showed that 1 exhibited a local thermodynamic relaxation due to the long alkyl side chains at a higher temperature than 2. In photoluminescence spectroscopy, 1 was found to be more emissive, with quantum yields being as high as 63.1 and 27.4% in solution and films, respectively, while those of 2 were 49.4 and 20.6%. Consequently, 1 was more thermally stable, stiffer, and more emissive than 2.