Modulating Electronic Properties of Dinitrosoarene Polymers

The possibilities for tuning of electronic, transport, and optical properties of the linear dinitrosobenzene polymer (1) are explored. The band gap (Eg) and optical spectrum of 1 are calculated using both GW-BSE corrected for zero-point vibrations and hybrid TD-DFT, with the former method predicting a value (2.41 eV) in excellent agreement with diffuse reflectance spectroscopy measurements (2.39 eV). GW-BSE is also used to evaluate the effects of solid-state packing, while comprehensive TD-DFT calculations are employed to study the effects of intra-polymer torsion, gold surface adsorption, substitution, and changes in the aromatic core of 1. Torsion is found to be an important factor in determining Eg and transport properties, and a strong effect of the environment on the exciton binding energies is identified. Extending the conjugation in the aromatic core is found to enhance transport properties and narrow Eg, identifying future synthetic targets. Atomic force microscopy and spectroscopic ellipsometry are used to study 1 adsorbed to a (111) gold surface (1@Au), with the latter method showing a significant narrowing of the band gap to 0.68 eV, in good agreement with TD-DFT predictions.