Tethered tertiary amines as solid-state n-type dopants for solution-processable organic semiconductors
A scarcity of stable n-type doping strategies compatible with facile processing has been a major impediment to the advancement of organic electronic devices. Localizing dopants near the cores of conductive molecules can lead to improved efficacy of doping. We and others recently showed the effectiveness of tethering dopants covalently to an electron-deficient aromatic molecule using trimethylammonium functionalization with hydroxide counterions linked to a perylene diimide core by alkyl spacers. In this work, we demonstrate that, contrary to previous hypotheses, the main driver responsible for the highly effective doping observed in thin films is the formation of tethered tertiary amine moieties during thin film processing. Furthermore, we demonstrate that tethered tertiary amine groups are powerful and general n-doping motifs for the successful generation of free electron carriers in the solid-state, not only when coupled to the perylene diimide molecular core, but also when linked with other small molecule systems including naphthalene diimide, diketopyrrolopyrrole, and fullerene derivatives. Our findings help expand a promising molecular design strategy for future enhancements of n-type organic electronic materials.
Additional Information© The Royal Society of Chemistry 2016. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. Received 5th November 2015, Accepted 6th December 2015. First published on 9th December 2015. This article is part of the themed collections: Global Energy Challenges: Solar Energy, Top 50 Articles of 2016: Energy and Catalysis and Top 50 Articles of 2016: Materials Chemistry and Nanoscience. This work was funded by the AFOSR MURI program under FA9550-12-1-0002. Portions of this research were carried out at the Molecular Foundry, a LBNL user facility supported by the Office of Science, BES, U.S. DOE, under Contract DE-AC02-05CH11231. Portions of this work were performed at the MRL Shared Experimental Facilities, which are supported by the MRSEC Program of the NSF under Award No. DMR 1121053; a member of the NSF-funded Materials Research Facilities Network (http://www.mrfn.org). B. R. gratefully acknowledges the DOD, AFOSR, for DOD-NDSEG fellowship support, 32 CFR 168a under contract FA9550-11-C-0028. M. J. R. thanks UC Regents, CSP Technologies, and the DOE (SCGF) for graduate fellowships. We thank Fred Wudl for helpful conversations. Author contributions: G. C. B., J. J. U., M. L. C., C. J. H., and R. A. S. conceptualized and guided the experiment. B. R., M. J. R., B. P., C.-K. M., S. F., G. C. B., J. J. U., M. L. C., C. J. H., and R. A. S. designed the molecules. M. J. R., B. P., C.-K. M., S. F. synthesized material and performed an analytical workup of these materials. E. E. P. and C.-K. M. performed EPR sample preparation and measurement and B. R. and E. E. P. performed EPR data analysis. S. N. P. and T. E. M. performed XPS sample preparation and measurement, and B. R. and T. E. M. performed XPS data analysis. B. R. performed optical characterization of the materials. All authors participated in discussion of scientific ideas, and B. R. wrote the manuscript.
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