Protonated [4n]pi and [4n+2]pi octaphyrins choose their Möbius/Hückel aromatic topology.
Protonation-triggered conformational changes of meso-octakis(pentafluorophenyl) [36]octaphyrin and [38]octaphyrin have been investigated. The X-ray crystal structures and (1)H NMR analyses revealed that the protonation process cuts off intramolecular hydrogen bonds between aminic and iminic pyrrole units and, at the same time, produces intermolecular hydrogen-bond network between aminic pyrrole unit and counter-anions. Such a replacement induces some pyrrole inversion, leading to Mobius aromatic conformation for [36]octaphyrin and to Huckel aromatic conformation for [38]octaphyrin. These protonated octaphyrins show similar structures only with a subtle difference in tilted pyrrole angles, which results in their different topologies. This feature strongly suggests that the macrocycles control their topologies by pyrrole rotation to gain [4n]pi Mobius or [4n+2]pi Huckel aromatic stabilization, depending on the number of pi-electrons. Detailed photophysical properties such as absorption/fluorescence, excited singlet/triplet state lifetimes, and two-photon absorption cross-section values have been presented for both protonated [36] and [38]octaphyrins in conjunction with their Mobius or Huckel aromaticity.
Spectroscopy Laboratory for Functional pi-Electronic Systems and Department of Chemistry, Yonsei University, Seoul 120-749, Korea.
Jong Min
JM
Lim
Jae-Yoon
JY
Shin
Yasuo
Y
Tanaka
Shohei
S
Saito
Atsuhiro
A
Osuka
Dongho
D
Kim
D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D011522:Protons
D011166:Porphyrins; D011522:Protons