ja7b06848_si_001.pdf (5.28 MB)
Chiral Peropyrene: Synthesis, Structure, and Properties
journal contribution
posted on 2017-08-22, 00:00 authored by Wenlong Yang, Giovanna Longhi, Sergio Abbate, Andrea Lucotti, Matteo Tommasini, Claudio Villani, Vincent J. Catalano, Aleksandr O. Lykhin, Sergey A. Varganov, Wesley A. ChalifouxHerein we describe the synthesis,
structure, and properties of
chiral peropyrenes. Using p-terphenyl-2,2″,6,6″-tetrayne
derivatives as precursors, chiral peropyrenes were formed after a
4-fold alkyne cyclization reaction promoted by triflic acid. Due to
the repulsion of the two aryl substituents within the same bay region,
the chiral peropyrene adopts a twisted backbone with an end-to-end
twist angle of 28° that was unambiguously confirmed by X-ray
crystallographic analysis. The chiral peropyrene products absorb and
emit in the green region of the UV–visible spectrum. Circular
dichroism spectroscopy shows strong Cotton effects (Δε
= ±100 M–1 cm–1 at 300 nm).
The Raman data shows the expected D-band along with a split G-band
that is due to longitudinal and transversal G modes. This data corresponds
well with the simulated Raman spectra of chiral peropyrenes. The chiral
peropyrene products also display circularly polarized luminescence.
The cyclization reaction mechanism and the enantiomeric composition
of the peropyrene products are explained using DFT calculations. The
inversion barrier for racemization was determined experimentally to
be 29 kcal/mol and is supported by quantum mechanical calculations.