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Structural properties of highly doped borazino polyphenylenes obtained through condensation reaction

Dosso, Jacopo, Marinelli, Davide, Demitri, Nicola and Bonifazi, Davide 2019. Structural properties of highly doped borazino polyphenylenes obtained through condensation reaction. ACS Omega 4 (5) , pp. 9343-9351. 10.1021/acsomega.9b00830

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Abstract

Here we describe the synthesis and spectroscopic and structural characterization of various borazine-doped polyphenylenes displaying high doping dosages (16–18%). Capitalizing on the condensation reaction approach, the desired products were formed using a mixture of p-phenylendiamine and aniline with BCl3, followed by the addition of an aryl lithium derivative. The use of mesityl lithium (MesLi) yields strained multiborazine derivatives, which proved to be unstable in the presence of moisture. However, when xylyl lithium (XylLi) was used, chemically stable multiborazines were obtained, with oligomers showing molecular weight up to 104, corresponding to 16–18 monomer units. While the dimer, trimer, and tetramer could be isolated as pure products and their structure characterized by mass and NMR analysis, higher oligomers could only be isolated as mixtures of B-hydroxy-substituted derivatives and characterized by gel permeation chromatography. The structures of the dimer and trimer derivatives were confirmed by X-ray analysis, which nicely showed the presence of the two and three borazine rings spaced by one and two 1,4-aryl bridges, respectively. Notably, the trimer forms a porous crystalline clathrate. The peripheral xylyl and phenyl moieties of each molecule intramolecularly embrace each other through C–H and π–π stacking interactions. Steady-state UV–vis absorption characterization suggested that the molecules are UV absorbers, with the extinction coefficient linearly scaling with the degree of oligomerization. On the other hand, low-emission quantum yields were obtained for all derivatives (<7%), suggesting that high BN-doping dosages dramatically affect the emission properties of the doped polyphenylenes.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Additional Information: Available Open Access under ACS AuthorChoice licence.
Publisher: American Chemical Society
ISSN: 2470-1343
Funders: European Union H2020
Date of First Compliant Deposit: 30 May 2019
Date of Acceptance: 6 May 2019
Last Modified: 30 Nov 2019 05:45
URI: http://orca.cf.ac.uk/id/eprint/122960

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