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Abstract Doping of polycyclic aromatic hydrocarbons (PAHs) with boron and/or nitrogen is emerging as a powerful tool to tailor the electronic structure and photophysical properties. AsN‐doped analogues of anthracene,N,N‐dihydrophenazines play important roles as redox mediators, battery materials, luminophores, and photoredox catalysts. Although benzannulation has been used successfully as a structural constraint to control the excited state properties, fusion of the N‐aryl groups to the phenazine backbone has rarely been explored. Herein, we report the first examples of dihydrophenazines, in which the N‐aryl groups are fused to the phenazine backbone via B←N Lewis pair formation. This results in structural rigidification, locking the molecules in a bent conformation, while also modulating the electronic structure through molecular polarization. B─N fusion inBNPz1−BNPz3induces a quinoid resonance structure with significant C─N(py) double bond character and reduces the antiaromatic character of the central pyrazine ring. Borylation also lowers the HOMO/LUMO (highest occupied/lowest unoccupied molecular orbital) energies and engenders bathochromic shifts in the emission. Further rigidification in the solid state gives rise to enhanced emission quantum yields, consistent with aggregation‐induced emission enhancement (AIEE) observed upon water addition to solutions in tetrahydrofuran (THF). The demonstrated structural control and fine‐tuning of optoelectronic properties are of great significance to potential applications as emissive materials and in photocatalysis.
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Linear Extension of Anthracene via B←N Lewis Pair Formation: Effects on Optoelectronic Properties and Singlet O 2 Sensitization
Abstract The functionalization of polycyclic aromatic hydrocarbons (PAHs) via B←N Lewis pair formation offers an opportunity to judiciously fine‐tune the structural features and optoelectronic properties, to suit the demands of applications in organic electronic devices, bioimaging, and as sensitizers for singlet oxygen generation. We demonstrate that the N‐directed electrophilic borylation of 2,6‐di(pyrid‐2‐yl)anthracene offers access to linearly extended acene derivativesPy‐BR(R=Et, Ph, C6F5). In comparison to indeno‐fused 9,10‐diphenylanthracene, the formal “BN for CC” replacement inPy‐BRselectively lowers the LUMO, resulting in a much reduced HOMO–LUMO gap. An even more extended conjugated system with seven six‐membered rings in a row (Qu‐BEt) is obtained by borylation of 2,6‐di(quinolin‐8‐yl)anthracene. FluorinatedPy‐BPfshows particularly advantageous properties, including relatively lower‐lying HOMO and LUMO levels, strong yellow‐green fluorescence, and effective singlet oxygen sensitization, while resisting self‐sensitized conversion to its endoperoxide.
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- PAR ID:
- 10445810
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 61
- Issue:
- 5
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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