Temperature-dependent conformational change of meso-hexakis(pentafluorophenyl) [28]Hexaphyrins(1.1.1.1.1.1) into Möbius structures.
At room temperature, meso-hexaaryl-substituted [28]hexaphyrins(1.1.1.1.1.1) in solution exist largely as an equilibrium between planar antiaromatic and distorted Möbius aromatic conformers. As the temperature decreases, the molecular structure changes into the distorted Möbius topology that commonly occurs in [28]hexaphyrins, which gives rise to longer excited singlet and triplet state lifetimes than planar antiaromatic [28]hexaphyrins. Temperature-dependent two-photon absorption measurements of [28]hexaphyrin indicate that the degree of aromaticity of Möbius [28]hexaphyrin is large, comparable to that of Hückel aromatic planar [26]hexaphyrin. Through our spectroscopic investigations, we have demonstrated that a subtle balance between the strains induced by the size of the [28]hexaphyrin macrocyclic ring and the energy stabilization contributed by pi-electron delocalization in the formation of distorted Möbius [28]hexaphyrin leads to the molecular structure change into the Möbius topology as the temperature decreases.
Kim
Kil Suk
KS
Department of Chemistry, Yonsei University, Seoul 120-749, Korea.
Yoon
Zin Seok
ZS
Ricks
Annie Butler
AB
Shin
Jae-Yoon
JY
Mori
Shigeki
S
Sankar
Jeyaraman
J
Saito
Shohei
S
Jung
Young Mee
YM
Wasielewski
Michael R
MR
Osuka
Atsuhiro
A
Kim
Dongho
D