We have investigated the aromaticity of singly twisted Möbius aromatic and doubly twisted Hückel antiaromatic bis(palladium(II)) octaphyrins in the lowest triplet state (T1) by spectroscopic measurements and quantum calculations. The T1 state of the singly twisted Möbius octaphyrin shows broad and weak absorption spectral features that are analogous to those of antiaromatic expanded porphyrins while the T1 state of the doubly twisted Hückel octaphyrin exhibits intense and distinct spectral features, indicating the aromatic nature. These results along with theoretical calculations support the hypothesis that the aromaticity is reversed in the T1 state. Furthermore, we show that the degree of structural smoothness affects the aromaticity reversal in the T1 state.
Bibliographical noteFunding Information:
The work at Yonsei University was supported by the Samsung Science and Technology Foundation (Project Number SSTF-BA1402-10). The quantum-chemical calculations were performed using the supercomputing resources of the Korea Institute of Science and Technology Information (KISTI). The work at Kyoto was supported by the JSPS (KAKENHI Grant Numbers 25220802 (Scientific Research (S)) and 26620081 (Exploratory Research)).
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