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

Abstract

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.

Rational design of near‐infrared absorbing organic dyes: Controlling the HOMO–LUMO gap using quantitative molecular orbital theory

“…Introducing a π‐donating NH 2 (X in Scheme ) substituent on the benzene ring (D2) increases its HOMO energy (C 6 H 4π,HOMO ), whereas a π‐accepting CN (Y in Scheme ) substituent (A2) lowers its LUMO energy (C 6 H 4π*,LUMO ), resulting in both cases in a decrease of Δ E frag H‐L (Fig. b) in qualitative agreement with recent studies . The HOMO arises from the antibonding combination of the occupied D1 π,HOMO and NH 2π,HOMO fragment orbitals, whereas the LUMO originates from the bonding combination of the unoccupied A1 π*,LUMO and CN π*, LUMO fragment orbitals.…”

Pyrene Molecular Orbital Shuffle—Controlling Excited State and Redox Properties by Changing the Nature of the Frontier Orbitals

“…From analysis of the intervalence charge transfer (IVCT) band in the absorption spectra and TD‐DFT calculations, they concluded that the pyrene‐ ( V= 2160 cm −1 ) and biphenyl‐ ( V= 2420 cm −1 ) bridged compounds are Robin–Day class‐II compounds, while the 4,5,9,10‐tetrahydropyrene‐ ( V= 2760 cm −1 ) bridged analogue was found to be a delocalized Robin–Day class‐III derivative. As a demonstration of our borylation‐based methodology (vide supra) we synthesized 2‐cyano‐7‐( N , N ‐diethylamino)pyrene ( F) and related mono‐substituted compounds . Indeed, as observed previously, the pure radiative lifetimes τ 0 were in the range of 40–140 ns (2‐( N , N ‐diethylamino)pyrene=40 ns; 2‐cyanopyrene=140 ns; 2‐cyano‐7‐( N , N ‐diethylamino)pyrene=65 ns), that is, about two orders of magnitude longer than that typical of 1‐substituted derivatives.…”

“…However, the HOMO−1 and LUMO+1 have nonzero contributions at the 2‐ and 7‐positions and, therefore, π‐donor or π‐acceptor substituents have a direct effect on these orbitals. As a result, we have already noted that, with suitably strong donors, the pyrene HOMO−1 orbital can be destabilized to the extent that it rises above the pyrene HOMO in energy and, likewise, with suitably strong acceptors, the LUMO+1 can be stabilized to the extent that it falls below the pyrene LUMO in energy. Thus, with appropriate substitution at the 2‐ and 7‐positions, we can reverse the order of HOMO/HOMO−1 and/or LUMO/LUMO+1 and, at the same time, adjust the band gap.…”

Recent developments in and perspectives on three-coordinate boron materials: a bright future

“…, R 2 N) at the 2- or 2,7-positions allows mixing with the HOMO–1 of pyrene (recall that mixing with the pyrene HOMO is also excluded due to its nodal properties) raising it in energy above what was the pyrene HOMO. 97–100 Thus, not only can we reverse the order of LUMO and LUMO+1, but also that of HOMO and HOMO–1 by judicious choice of substituents.…”