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.