The Extension of Baird's Rule to Twisted Heteroannulenes: Aromaticity Reversal of Singly and Doubly Twisted Molecular Systems in the Lowest Triplet State

摘要

We have investigated the aromaticity of singly twisted Mobius aromatic and doubly twisted Huckel antiaromatic bis(palladium(II)) 36octaphyrins in the lowest triplet state (T-1) by spectroscopic measurements and quantum calculations. The T-1 state of the singly twisted Mobius 36 octaphyrin shows broad and weak absorption spectral features that are analogous to those of antiaromatic expanded porphyrins while the T-1 state of the doubly twisted Huckel 36 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 T-1 state. Furthermore, we show that the degree of structural smoothness affects the aromaticity reversal in the T-1 state.