Manipulation of Donor–Acceptor Interactions in Carbazole-Based Emitters by Chromophore Choice To Achieve Near-UV Emission

Abstract

New organic materials containing a cyano-functionalized carbazole moiety at one end linked to different chromophores such as fluorene, carbazole, and triphenylamine at the other end through an acetylene spacer are synthesized and characterized by photophysical, electrochemical, thermal, and electroluminescence studies. A meta-like linkage at the C-2 and C-7 atoms of the central carbazole moiety and the choice of chromophore restricted the emission to the near-ultraviolet region. The photophysical properties of the compounds depend on the nature of the chromophore attached to the carbazole unit. A triphenylamine-substituted derivative exhibited the longest wavelength emission in the series, attributable to the elongated conjugation and electron richness of triphenylamine, whereas the phenyl- and fluorene-functionalized molecules showed the shortest wavelength emissions with vibronic patterns. The compounds containing carbazole and triphenylamine units exhibited positive solvatochromism in their fluorescence spectra, and this behavior is characteristic of charge transfer from a donor to an acceptor. A fluorene derivative containing cyano substituents at the carbazole and fluorene moieties exhibited the best electroluminescence characteristics in the series, probably because of balanced charge transport and effective confinement of the excitons in the emissive layer. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.