title: Investigation of aromaticity and photophysical properties in [18]/[20]π porphycene derivatives.
abstract: In this study, we have investigated the relationship between aromaticity and photophysical properties of trifluoromethyl-substituted [18]/[20]π porphycenes by using theoretical calculations and various spectroscopic methodologies. Interestingly, we have found that the HOMO-LUMO gap of [20]π porphycene is larger than that of [18]π porphycene, which is in a sharp contrast with those of typical [4n]/[4n+2]π porphyrinoids. Based on our observations, we demonstrate that the origin of this contrasting feature of [20]π porphycene arises from the uniquely large energy splitting between LUMO and LUMO+1 of [18]π porphycene compared with other aromatic [4n+2]π porphyrinoids with nearly degenerate LUMO/LUMO+1. Consequently, we can propose that the energy difference between LUMO and LUMO+1 levels of aromatic [4n+2]π porphyrinoids is an important factor in determining the electronic nature of their corresponding antiaromatic [4n]π porphyrinoids. Moreover, to the best of our knowledge, this is the first study to illustrate the photophysical properties of porphycenes with [4n]π electronic circuits.
authors.affiliation: Department of Chemistry, Yonsei University, Seoul 120-749, Korea.
authors.forename: Kil Suk
authors.initials: KS
authors.lastname: Kim
authors.forename: Young Mo
authors.initials: YM
authors.lastname: Sung
authors.forename: Takashi
authors.initials: T
authors.lastname: Matsuo
authors.forename: Takashi
authors.initials: T
authors.lastname: Hayashi
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim