Crystal structure and ON-OFF polymerization mechanism of poly(1,4-phenyleneazine-N,N-dioxide), a possible wide bandgap semiconductor

Abstract

Crystal and molecular structure of poly(1,4-phenyleneazine-N,N-dioxide) (PDNB, 1), obtained from polymerization of 1,4-dinitrosobenzene, is investigated by X-ray powder diffraction (XRPD) and DFT calculations. Starting with the determined crystal structure, we have calculated the electronic structure of the polymer, which reveals that 1 is potentially a wide-bandgap (WBG) semiconductor with a band gap of 2.3 eV. Its calculated electronic spectrum with the absorbance at 400 nm is in good agreement with the experimental data. A highly organized crystal structure with linear chains of polymer indicates possible anisotropic electronic properties that could be useful in molecular photoelectronics (e.g OLEDs). Photolysis of 1 at cryogenic temperatures yields dinitrosobenzene monomers, which re-polymerize at higher temperatures. After this reversible photo-thermal cycle, the starting polymorph of 1 is recovered. Thermal analysis (TG/DSC/DTA) and in situ XRPD measurements show the high thermal stability of 1 until around 150 °C.