Modulating Electronic Properties of Dinitrosoarene Polymers

30 December 2021, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

We present a comprehensive analysis on how the electronic structure and the optical properties of an organic polymer can be modulated, based on the example of the dinitrosobenzene polymer (1). Using a combination of computational and experimental tools, we explore the effects of solid-state packing, backbone torsion, surface adsorption, the conjugation in the aromatic core, and substituents. The band gap (Eg) and optical spectrum of 1 are calculated using both GW-BSE with zero-gap renormalization (ZGR) and hybrid TD-DFT, with the former method predicting a value (2.41 eV) in excellent agreement with our diffuse reflectance spectroscopy measurements (2.39 eV). Using GW-BSE-ZGR, changes occurring upon solidstate packing are separated into a contribution arising from (i) the change in the torsional angle and (ii) the change in the screened Coulombic interaction, which strongly effects the exciton binding energies. Comprehensive hybrid TD-DFT calculations find that the effects of substituents on Eg and on transport properties can mostly be explained through changes in the torsional angle, and predict a linear dependence between it and Eg. 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.

Keywords

GW approximation
GW-BSE
nitroso
band gap engineering
organic polymers
organic semiconductors

Supplementary materials

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Supplementary information for Modulating Electronic Properties of Dinitrosoarene Polymers
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Supplementary information for the " Modulating Electronic Properties of Dinitrosoarene Polymers" manuscript, containing: (i) Optimized geometries of all structures (POSCAR) (ii) Benchmarking results for geometry optimization, GW calculations, and ZGR calculations. (iii) Calculated conductivity of C1, full phonon band structure of C1, TD-HSE predicted optical spectra, Hammett graph for dinitroso dimers and polymers.
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