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(188.8.131.52.1.1). 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.
Bibliographical noteFunding Information:
This research at Yonsei University supported by the Global Research Laboratory Program (2013K1A1A2A02050183) funded by the Ministry of Science, ICT & Future, Korea. The work at Kyoto was supported by JSPS KAKENHI Grant Numbers (25220802 and 25620031). H. M. acknowledges a JSPS Fellowship for Young Scientists. The quantum calculations were performed using the supercomputing resources of the Korea Institute of Science and Technology Information (KISTI).
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