Long-range through-space charge transfer in a pH-responsive mixed cyclophane of pyridine and teropyrene

Place: Hinarejos room, ground floor, IMDEA Nanociencia.

Abstract: 

Teropyrene, a C36 PAH, is the largest PAH to have been systematically bent out of planarity
through its incorporation into a series of [n]cyclophaness (those that consist of a single
aromatic system and a single aliphatic bridge) where n = 7-10.[1] In this series of cyclophanes,
the end-to-end bend in the teropyrene ranges from q = 145° to 178°. The teropyrene system
undegoes highly regioselective electrophilic aromatic substitution (bromination) and this can
be understood in terms of a combination of steric and electronic effects. Furthermore, the
chemical reactivity of the teropyrene system toward bromination increases substantially as it
becomes more bent.[2]
More recently, a large, strained (SE = 44.2 kcal/mol) and conformationally flexible mixed
[3.3]cyclophane of pyridine and teropyrene was synthesized using two intramolecular Wurtz
coupling reactions and an unprecedented Scholl reaction between the unreactive 2 positions
of the pyrene systems in a triply-bridged pyrenophane.[3] Protonation of the pyridine unit
results in a greatly enhanced preference for nesting in the cavity of the highly bent teropyrene
system (qcalc = 162.6°) and emergence of a charge transfer absorption band (lmax = 592 nm)
due to a long range (5.0-5.5 Å), through-space intramolecular transition between the
teropyrene and pyridinium units, which does not exist in the neutral cyclophane.

References
1. Unikela, K. S.; Ghods Ghasemabadi, P.; Houska, V.; Dawe, L. N.; Zhao, Y.; Bodwell, G. J.
“Chem. – Eur. J. 2021, 27, 390–400
2. Unikela, K. S.; Roemmele, T. L.; Houska, V.; McGrath, K. E.; Tobin, D. M.; Dawe, L. N.;
Boeré, R. T.; Bodwell, G. J. Angew. Chem. Int. Ed. 2018, 57, 1707–1711.
3. Ghods Ghasemabadi, P.; Tabasi, Z. A.; Salari, P.; Zhao, Y.; Bodwell, G. J. Chem. – Eur. J.
2023, Early View, DOI: 10.1002/chem.202302404.