Pyrene-based asymmetric hexaarylbenzene derivatives: Synthesis, crystal structures, and photophysical properties

Hexaarylbenzenes (HAB) and their derivatives have attracted considerable attention due to their fantastic molecular geometry and various applications in materials science. Herein, a set of novel, pyrene-based, asymmetric hexaarylbenzene molecules 3a–c and 10 were synthesized and fully characterized by using ¹H/¹³C NMR, single crystal X-ray diffraction, high-resolution mass spectra (HRMS), UV–Vis and fluorescence spectroscopy, as well as density functional theory (DFT) calculations. The compounds show tunable-emission color from violet (366 nm) to deep blue emission (407 nm) following the order of 10 < 3a < 3b < 3c in solution, and the pyrene-based asymmetric hexaarylbenzenes show a red-shift to the (deep) blue region (in the range from 406 to 466 nm) with a narrow full width at half-maximum (FWHM) emission spectrum in films. On the other hand, as the expanding π-conjugated molecular frameworks decreased in the order of 3c > 3b > 3a > 10 > hexaphenylbenzene (HPB), the asymmetric hexaarylbenzenes exhibited clearer aggregation-induced emission characterestics. In addition, DFT calculations indicated that there is strong electronic communication between the pyrene unit and the neighboring phenyl rings by a through-space charge-transfer process, which would play a curial role in lowering the quantum yield in the molecular aggregation state. Thus, this article provides an efficient synthetic strategy on how to design and synthesise high-performance pyrene-based hexaarylbenzene derivatives with narrow FWHM bands for potential applications in organic electronics.