Phenanthroimidazole-based monomers: synthesis, properties and self-polymerization

Phenanthroimidazole-based monomers with reactive vinyl groups were synthesized, and their thermal, optical, photophysical and electrochemical properties were investigated. The monomers exhibited high thermal stability with 5% weight loss temperatures (T_d) ranging from 378 to 409 °C. Thermal degradation of the polymerization products apparently takes place in this temperature range. The solutions of the monomers exhibit emission peaks in the range from 388 to 398 nm. In the solid state, the emission of these molecules shows red shift which is coherent with the similar red shifts of the corresponding absorption spectra. Ionization potential values of the compounds estimated by cyclic voltammetry were found to be close and varied in the range from 5.44 to 5.63 eV. Solid-state ionization potentials estimated by photoelectron emission spectrometry varied in the range from 5.54 to 5.66 eV. Self-polymerization of the synthesized monomers was demonstrated by differential scanning calorimetry. The number average molecular weights of the polymerization products of monomers containing substituents at phenyl rings linked to C-2 and N-1 positions of imidazole ring were found to be 100,100 and 196,000, respectively. The apparent activation energy and pre-exponential factor of self-polymerization were found to be dependent on conversion degree. The values of activation energy for self-polymerization of monomers varied in the range from 78.7 to 136.0 kJ/mol (estimated by Ozawa method) and from 78.3 to 139.0 kJ/mol (estimated by Kissinger method).