Structural properties of highly-doped borazino polyphenylenes obtained through condensation reaction

Jacopo Dosso, Davide Marinelli, Nicola Demitri, Davide Bonifazi
ACS Omega2019, 4 (5), 9343-9351
DOI: 10.1021/acsomega.9b00830


Here we describe the synthesis, 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 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 GPC. The structure 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 p-p 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.

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