Synthesis, Photophysical, and Electrochemical Properties of Pyrenes Substituted with Donors or Acceptors at the 4- or 4,9-Positions

We report herein an efficient and direct functionalization of the 4,9-positions of pyrene by Ir-catalyzed borylation. Three pinacol boronates (-Bpin), including 4-(Bpin)-2,7-di­(tert-butyl)­pyrene (5), 4,9-bis(Bpin)-2,7-di­(tert-butyl)­pyrene (6), and 4,10-bis(Bpin)-2,7-di­(tert-butyl)­pyrene (7), were synthesized. The structures of 6 and 7 have been confirmed by single-crystal X-ray diffraction. To demonstrate the utility of these compounds, donor (NPh₂)-substituted compounds 4-diphenylamino-2,7-di­(tert-butyl)­pyrene (1) and 4,9-bis(diphenyl­amino)-2,7-di­(tert-butyl)­pyrene (2) have been synthesized on a gram scale. Acceptor (BMes₂)-substituted compounds 4,9-bis(BMes₂)­pyrene (3) and 4,9-bis(BMes₂)-1,2,3,6,7,8-hexa­hydro­pyrene (4) were synthesized for comparison. The photophysical and electrochemical properties of compounds 1–4 have been studied both experimentally and theoretically. The S₀ → S₁ transitions of the 4- or 4,9-disubstituted pyrenes, 1–3, are allowed, with moderate fluorescence quantum yields and radiative decay rates. The photophysical and electrochemical properties of 1–3 were compared with the 2,6-naphthalenylene-cored compound 4 as well as the previously reported 2,7- and 1,6- pyrenylene-cored compounds.