Structure–property investigations in urea tethered iodinated triphenylamines

Hossain, M. S., Ahmed, F., Karakalos, S. G., Smith, M. D., Pant, N., Garashchuk, S., Greytak, A. B., Docampo, P. and Shimizu, L. S. (2022) Structure–property investigations in urea tethered iodinated triphenylamines. Physical Chemistry Chemical Physics, 24(31), pp. 18729-18737. (doi: 10.1039/D2CP01856J) (PMID:35899998)

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Herein, we report structural, computational, and conductivity studies on urea-directed self-assembled iodinated triphenylamine (TPA) derivatives. Despite numerous reports of conductive TPAs, the challenges of correlating their solid-state assembly with charge transport properties hinder the efficient design of new materials. In this work, we compare the assembled structures of a methylene urea bridged dimer of di-iodo TPA (1) and the corresponding methylene urea di-iodo TPA monomer (2) with a di-iodo mono aldehyde (3) control. These modifications lead to needle shaped crystals for 1 and 2 that are organized by urea hydrogen bonding, π⋯π stacking, I⋯I, and I⋯π interactions as determined by SC-XRD, Hirshfeld surface analysis, and X-ray photoelectron spectroscopy (XPS). The long needle shaped crystals were robust enough to measure the conductivity by two contact probe methods with 2 exhibiting higher conductivity values (∼6 × 10−7 S cm−1) compared to 1 (1.6 × 10−8 S cm−1). Upon UV-irradiation, 1 formed low quantities of persistent radicals with the simple methylurea 2 displaying less radical formation. The electronic properties of 1 were further investigated using valence band XPS, which revealed a significant shift in the valence band upon UV irradiation (0.5–1.9 eV), indicating the potential of these materials as dopant free p-type hole transporters. The electronic structure calculations suggest that the close packing of TPA promotes their electronic coupling and allows effective charge carrier transport. Our results show that ionic additives significantly improve the conductivity up to ∼2.0 × 10−6 S cm−1 in thin films, enabling their implementation in functional devices such as perovskite or solid-state dye sensitized solar cells.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Docampo, Dr Pablo and Pant, Dr Namrata
Authors: Hossain, M. S., Ahmed, F., Karakalos, S. G., Smith, M. D., Pant, N., Garashchuk, S., Greytak, A. B., Docampo, P., and Shimizu, L. S.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Physical Chemistry Chemical Physics
Publisher:Royal Society of Chemistry
ISSN (Online):1463-9084
Published Online:18 July 2022
Copyright Holders:Copyright © 2022 Owner Societies
First Published:First published in Physical Chemistry Chemical Physics 24(31): 18729-18737
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
310679Hybrid Perovskite Heterojunctions (AoE ENG Materials & Manufacturing)Pablo DocampoEngineering and Physical Sciences Research Council (EPSRC)EP/T010568/1Chemistry