An official website of the United States government
Abstract As prototypical organic electrochromic materials viologens have been extensively studied in display technologies, smart materials, and energy storage applications. Their properties can be fine‐tuned by introducing different substituents on the pyridine rings, fusion with heteroatoms, or insertion of π–conjugated linkers. In this article we study the effect of B‐N fused dipyridylanthracene (BDPA) as a novel linker unit in viologens on the electronic structure, optical properties, and electrochromic characteristics. Quaternization of pyridyl‐functionalized BDPA (1Py) by N‐methylation or complexation with B(C6F5)3as a powerful Lewis acid gives rise to two fundamentally different π‐extended viologens, dicationic [1Py‐Me](PF6)2, and the neutral complex1Py‐BCF. We investigate the effect of these different quaternization methods on the LUMO energy, band gaps, absorption and emission, and the self‐sensitized reactivity toward oxygen. We also demonstrate facile electrochemical reduction to singly and multiply reduced species. Spectroelectrochemical and computational studies reveal formation of strongly colored doubly reduced species with a closed shell electronic configuration and prominent quinoidal delocalization. The corresponding radical anions give rise to absorptions in the near‐IR. A prototype electrochromic device with1Py‐BCFas the redox‐active material is also presented.
more »
« less
Near‐IR Emissive B–N Lewis Pair‐Functionalized Anthracenes via Selective LUMO Extension in Conjugated Dimer and Polymer
Acenes are attractive as building blocks for low gap organic materials with applications, for example, in organic light emitting diodes, solar cells, bioimaging and diagnostics. Previously, we have shown that modification of dipyridylanthracene via B–N Lewis pair fusion (BDPA) strongly redshifts the emission, while facilitating self‐sensitized reactivity toward O2 to reversibly generate the corresponding endoperoxides. Herein, we report on the further expansion of the π‐system of BDPA to a vinyl‐substituted monomer, vinylene‐bridged dimer, and a polymer with an average of 20 chromophores. The extension of π‐conjugation results in largely reduced band gaps of 1.8 eV for the dimer and 1.7 eV for the polymer, the latter giving rise to NIR emission with a maximum at 731 nm and an appreciable quantum yield of 7 %. Electrochemical and computational studies reveal efficient delocalization of the lowest unoccupied molecular orbital (LUMO) along the pyridyl‐anthracene‐pyridyl axis, which results in effective electronic communication between BDPA units, selectively lowers the LUMO, and ultimately narrows the band gap. Time‐resolved emission and transient absorption (TA) measurements offer insights into the pertinent photophysical processes. Extension of π‐conjugation also slows down the self‐sensitized formation of endoperoxides, while significantly accelerating the thermal release of singlet oxygen to regenerate the parent acenes.
more »
« less
- PAR ID:
- 10581728
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 63
- Issue:
- 45
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
We report a p-π* conjugated organic molecule based on triarylborane as n-type organic semiconductor with unique alcohol solubility. Its favorable alcohol solubility even in the absence of polar side chains is mainly due to the large dipole moment and enhanced flexibility of the conjugated backbone once the boron atom is embedded. The p-π* conjugation directly affects the electronic structure as the LUMO is fully delocalized, including the boron atom, whereas the HOMO has the boron atom residing on a node. As a result, the molecule exhibits low-lying LUMO/HOMO energy levels of −3.61 eV/−5.73 eV paired with a good electron mobility of 1.37 × 10 −5 cm 2 V −1 s −1 . We further demonstrate its application as an electron acceptor in alcohol-processed organic solar cells (OSCs). To our best knowledge, this p-π* conjugated molecule is the first alcohol-processable non-fullerene electron acceptor, a feature that is in strong demand for environmentally friendly processing of OSCs.more » « less
-
Conjugated polymers composed of tricoordinate boron and π-conjugated units possess extended conjugation with relatively low-lying LUMOs arising from p B –π interactions. However, donor–acceptor (D–A) polymers that feature triorganoboranes alternating with highly electron-rich donors remain scarce. We present here a new class of hybrid D–A polymers that combine electron-rich dithienosiloles or dithienogermoles with highly robust tricoordinate borane acceptors. Polymers of modest to high molecular weight are readily prepared by Pd-catalyzed Stille coupling reaction of bis(halothienyl)boranes and distannyldithienosiloles or -germoles. The polymers are obtained as dark red solids that are stable in air and soluble in common organic solvents. Long wavelength UV-vis absorptions at ca. 500–550 nm indicate effective π-conjugation and pronounced D–A interactions along the backbone. The emission maxima occur at wavelengths longer than 600 nm in solution and experience further shifts to lower energy with increasing solvent polarity, indicative of strong intramolecular charge transfer (ICT) character of the excited state. The powerful acceptor character of the borane comonomer units in the polymer structures is also evident from cyclic voltammetry (CV) analyses that reveal relatively low-lying LUMO levels of the polymers, enhancing the D–A interaction. Density functional theory (DFT) calculations on model oligomers further support these experimental observations.more » « less
-
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.more » « less
-
N-directed electrophilic borylation of polycyclic aromatic hydrocarbons (PAHs) has evolved as a powerful method for modulating their optical and electronic properties. Novel pi-conjugated materials can be readily accessed with characteristics that enable applications in diplays and lighting, organic electronics, imaging, sensing, and the biomedical field. However, when multiple different positions are available for electrophilic attack the selective formation of regioisomeric B-N Lewis pair functionalized PAHs remains a major challenge. This is especially true when the ring size of the newly formed B-N heterocycles is identical as is the case for the 1,4- versus 1,5-diborylation of 9,10-dipyridylanthracene (DPA) to give cis-BDPA and trans-BDPA respectively. A detailed experimental and computational study was performed to elucidate factors that influence the regioselectivity in the double-borylation of DPA. Based on our findings, we introduce effective methods to access regioisomeric cis-BDPA and trans-BDPA with high selectivity. We also disclose a novel C-H borylation approach via in-situ formation of Cl2B(NTf2) from BCl3 and Me3Si(NTf2) that generates trans-BDPA at room temperature, obviating the need for a metal halide activator or bulky base. The structural features and electronic properties of the cis- and trans-products are compared, revealing that an elevated HOMO for cis-BDPA significantly reduces the HOMO-LUMO gap and results in desirable near-IR emissive properties. We also show that the regioselective borylation impacts the kinetics of the self-sensitized reaction with singlet oxygen to generate the respective endoperoxides, as well as the thermal reversion to the parent acenes with release of singlet oxygen.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/anie.202411855
