Synthesis and Photophysics of a 2,7-Disubstituted Donor–Acceptor Pyrene Derivative: An Example of the Application of Sequential Ir-Catalyzed C–H Borylation and Substitution Chemistry

We report a general and selective
method to synthesize 2,7-disubstituted
pyrene derivatives containing two different substituents by sequential
Ir-catalyzed borylation and substitution chemistry. To demonstrate
the utility of our approach, we synthesized 2-cyano-7-(N,N-diethylamino)­pyrene (3), a pyrene
analogue of the widely studied chromophore 4-(N,N-dimethylamino)­benzonitrile (DMABN). Compound 3 and the monosubstituted compounds 2-(N,N-diethylamino)­pyrene (1) and 2-cyanopyrene
(2) have been structurally characterized. Their electronic
and optical properties have been studied by a combination of absorption
and emission spectroscopies, lifetime and quantum yield measurements,
and modeling by DFT and TD-DFT. The photophysical properties of 3 are compared to those of DMABN and 2-cyano-7-(N,N-dimethylamino)-4,5,9,10-tetrahydropyrene, and
we show that 2,7-disubstituted pyrene is a moderately effective π-bridge
for the construction of donor–acceptor compounds. It is also
shown that donor or acceptor groups are only effective at the 2,7-positions
of pyrene if they are suitably strong, leading to a switch in the
energetic ordering of the HOMO–1 and HOMO or the LUMO and LUMO+1
of pyrene, respectively.