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. 2016 Mar 1;7(3):2239-2245.
doi: 10.1039/c5sc04263a. Epub 2015 Dec 8.

Switchable π-electronic network of bis(α-oligothienyl)-substituted hexaphyrins between helical versus rectangular circuit

Juwon Oh  1 , Hirotaka Mori  2 , Young Mo Sung  1 , Woojae Kim  1 , Atsuhiro Osuka  2 , Dongho Kim  1
Affiliations

Switchable π-electronic network of bis(α-oligothienyl)-substituted hexaphyrins between helical versus rectangular circuit

Juwon Oh et al. Chem Sci. .

Abstract

The switching phenomena of conformation with π-electronic network through deprotonation-protonation processes were investigated by employing a series of 5,20-bis(α-oligothienyl) substituted hexaphyrins(1.1.1.1.1.1). They showed significant changes in the absorption and emission spectra with deprotonation, and returned to the initial state with protonation. Through NMR measurements and single crystal X-ray diffraction analysis, we found that the 5,20-bis(α-oligothienyl) substituted hexaphyrins, which possess acyclic, helical electronic networks involving oligothienyl chains in dumbbell conformations (type-I) in a neutral form, underwent effective deprotonation upon treatment with tetrabutylammonium fluoride (TBAF) to generate the corresponding dianions, which display cyclic electronic networks with enhanced aromaticity in rectangular conformations (type-II). Our quantum calculation results provide an unambiguous description for the switchable conformation and π-conjugation, which revealed that a deprotonation-induced enhanced aromatic conjugation pathway is involved in the switchable π-electronic network.

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Figures

Chart 1
Chart 1. Molecular structures of type-I and type-II [26]hexaphryins and the series of 5,20-bis(α-oligothienyl) substituted [26]hexaphyrins, T1–T4.
Scheme 1
Scheme 1. Deprotonation of [26]hexaphyrins (a): 1 and (b): Tn.
Fig. 1
Fig. 1. Steady-state absorption spectra of T1–T4 in CH2Cl2 with and without TBAF.
Fig. 2
Fig. 2. 1H NMR spectra of T2 in THF-d8 in the (a) absence of TBAF and (b) presence of an excess amount of TBAF. * and # represent peaks due to residual solvent and the tetrabutylammonium cation, respectively.
Fig. 3
Fig. 3. Femtosecond time-resolved transient absorption spectra and decay profiles (inset) of T12––T42– in CH2Cl2.
Fig. 4
Fig. 4. Optimized structures of (a) T2 and (b) T22– from the top and side view and energy level diagrams with molecular orbitals of (c) T2 and (d) T22–. meso-Pentafluorophenyl groups are omitted for clarity in the side view figures.
Scheme 2
Scheme 2. Switchable conformation and π-electronic network of Tn by deprotonation–protonation.
See this image and copyright information in PMC

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