1,3,2-benzodiazaboroles with 1,3-pentafluorophenyl and tetrafluoropyridyl substituents as building blocks in luminescent compounds
Résumé
The reaction of N-4′-trimethylsilylphenyl-3,6-di-tert-butylcarbazole (3) or N-5′-trimethylsilylthien-2′-yl-3,6-di-tert-butylcarbazole (4) with boron tribromide and subsequently with triphenylphosphane afforded the dibromoborylphenylcarbazole-phosphane adduct 5 or its thiophene derivative 6 as colorless solids. These adducts were converted into the new benzodiazaborole derivatives 7 and 8 by treatment with N,N′-bis(pentafluorophenyl)-o- phenylenediamine (1) and 2,2,6,6-tetramethylpiperidine in hot toluene (52 or 45 % yield). The analogous compounds 9 and 10 were obtained by condensing precursors 5 and 6 with bis(N,N′-2,3,5,6-tetrafluoropyrid-4-yl)-o- phenylenediamine (2) in the presence of the piperidine derivative in 35 and 16 % yield. Compounds 7-10 were characterized by NMR spectroscopy (1H, 11B, 13C, 19F) and mass spectrometry. The molecular structure of 8 was elucidated by X-ray diffraction analysis. The borylated systems show intense blue luminescence upon UV irradiation. In contrast to π-donating 1,3-diethyl- and 1,3-diphenyl-1,3,2-benzodiazaboroles, derivatives with fluoroaryl substituents at the ring nitrogen atoms are potent π acceptors when connected to a carbazole donor through suitable π-conducting spacers. Thus, molecules of type A show low-energy emission bands from charge-transfer (CT) transitions with large Stokes shifts and pronounced solvatochromism.