New Functional Organoboron Materials for Optoelectronics and Energy Conversion
Final Report Abstract
Sophisticatedly designed aryl boranes are key building blocks for next-generation organic optoelectronic materials. Our aim was to combine the expertise of 2 German and 2 Chinese teams to design and synthesize new boron-based polycyclic aromatic hydrocarbons (PAHs) and to explore their applications in optoelectronic devices. We addressed all aims of the project and achieved all 3 main goals, in some cases exceeding our initial expectations by engaging additional collaborators, PhD students, and postdocs, and utilizing additional support from the China Scholarship Council and the Humboldt Foundation. Thus, as planned, we: i) developed considerable new and widely applicable synthetic methodology for the preparation of novel B-PAH and B,X-PAH systems (and for unsymmetricallysubstituted triarylboranes), and investigated their use in OLEDs and organic photovoltaic devices (OPVs); (ii) developed new strategies to obtain stable B-PAH’s based on borole building blocks (including borafluorenes, and CF3-substituted and heteroatom-containing borafluorenes); and (iii) designed and synthesized new boron-containing polymers, in particular based on B,X-chelate units, for OPVs. Wagner’s group prepared novel helicenes doped with 2 boron atoms, whereas Marder prepared donoracceptor type helicenes bearing triarylboron substituents. Wagner developed three new atom-efficient and modular synthesis protocols for B,N-, B,O-, B,N,O-, and B,S-doped PAHs and prepared and characterized novel NB2-, NBO-, and B2S4-containing PAH’s. Marder’s group also prepared a novel orthotetra-Bmes2-substituted perylene displaying 4 reversible reductions. Methodology was developed in the Marder group for the synthesis of useful BArAr’Ar’’ systems, including post-functionalization of the parapositions with different substituents to control electronic properties as well as water solubility. These systems have outstanding potential for numerous current and future applications from optical and electronic materials to bioimaging and other bio-applications. The use of CF3-substituents in triarylboranes and borafluorenes was shown to enhance significantly and simultaneously electron-acceptor properties, thermal stability, and stability to air, an advance which offers potential for many applications. The first demonstration of thermally activated delayed fluorescence (TADF) from a borafluorene was demonstrated, and the first OLED devices employing borafluorenes as the emitter material were also reported (Wang, Marder). As an alternative approach to enhancing electron acceptor properties, novel phenylpyridyl-fused boroles (N-containing borafluorenes) were prepared including unusual tetramers, arising from strong intermolecular N-B interactions, and oligomers (the latter partially dissociate in solution giving rise to dual fluorescence), depending on the position of the N atom within the borafluorene core. Based on initial computational studies delineating key aspects influencing singlet-triplet energy gaps, a series of donor-π-acceptor (D-π-A) molecules exhibiting thermally activated delayed fluorescence (TADF) with B(FXyl)2 as the acceptor moiety was initially designed and then synthesized and characterized, with excellent agreement between experimental results and the theoretical predictions. Some of these compounds are now being incorporated into OLEDs in a new collaboration with a research group in Kyoto. Finally, a new N–B←N-containing acceptor building block was developed for applications in conjugated polymers (Liu, Marder). The homopolymers were employed in all-polymer solar cells (All-PCS) and show promising properties for applications in organic semiconductors.
Publications
- (2020). Computationally Guided Molecular Design to Minimize the LE/CT Gap in D‐π‐A Fluorinated Triarylboranes for Efficient TADF via D and π‐Bridge Tuning. Advanced functional materials, 30(31), 2002064
A. K. Narsaria, F. Rauch, J. Krebs, P. Endres, A. Friedrich, I. Krummenacher, H. Braunschweig, M. Finze, J. Nitsch, F. M. Bickelhaupt, T. B. Marder
(See online at https://doi.org/10.1002/adfm.202002064) - (2020). Highly stable, readily reducible, fluorescent, trifluoromethylated 9‐borafluorenes. Chemistry–A European Journal, 26(56), 12794-12808
F. Rauch, S. Fuchs, A. Friedrich, D. Sieh, I. Krummenacher, H. Braunschweig, M. Finze, T. B. Marder
(See online at https://doi.org/10.1002/chem.201905559) - (2021). Highly Emissive 9‐Borafluorene Derivatives: Synthesis, Photophysical Properties and Device Fabrication. Chemistry–A European Journal, 27(20), 6274-6282
X. Chen, G. Meng, G. Liao, F. Rauch, J. He, A. Friedrich, T. B. Marder, N. Wang, P. Chen, S. Wang, X. Yin
(See online at https://doi.org/10.1002/chem.202005185) - (2021). N–B← N Bridged bithiophene: A building block with reduced band gap to design n-type conjugated polymers. Macromolecules, 54(14), 6718-6725
X. Shao, J. Wang, T. B. Marder, Z. Xie, J. Liu, L. Wang
(See online at https://doi.org/10.1021/acs.macromol.1c01055) - (2021). Phenylpyridyl‐Fused Boroles: A Unique Coordination Mode and Weak B− N Coordination‐Induced Dual Fluorescence. Angewandte Chemie International Edition, 60(9), 4833-4840
J. He, F. Rauch, A. Friedrich, J. Krebs, I. Krummenacher, R. Bertermann, J. Nitsch, H. Braunschweig, M. Finze, T. B. Marder
(See online at https://doi.org/10.1002/anie.202013692) - (2021). Synthesis of Highly Functionalizable Symmetrically and Unsymmetrically Substituted Triarylboranes from Bench‐Stable Boron Precursors. Chemistry–A European Journal, 27(35), 9094-9101
M. Ferger, S. M. Berger, F. Rauch, M. Schönitz, J. Rühe, J. Krebs, A. Friedrich, T. B. Marder
(See online at https://doi.org/10.1002/chem.202100632)
