New long-chain donor-acceptor-donor pyromellitic diimide (PMDI) derivatives. A combined theoretical and experimental study

Abstract This study involves the electrochemical, thermal and photophysical profiling of new pyromellitic diimide (PMDI) derivatives containing alkyl chains of different sizes. The photophysical investigation shows that all compounds exhibited absorption in the UV-B region (∼290 nm). The band-gaps were calculated by onset peak values of around 4.03 eV. The compounds are photoactive in the UV-A region (312–328 nm) with a small solvatochromic effect in the excited state (Δλ em  = 16 nm). The electrochemical studies revealed that the reduction of the bisimide moiety showed two waves due to the formation of both the radical anion and a dianion. On the other hand, oxidation showed two waves due to the formation of radical cations and dications. The thermal properties were measured by differential thermal analysis (DTA) and thermogravimetric analysis (TGA), and the materials showed high thermal stability (T d  > 300 °C). Theoretical calculations were also performed to study the geometry and charge distribution of these compounds in their ground and excited electronic states. No significant changes in the absorption and emission maxima were found by changing the solvent or substituents attached to the PMDI structure.