title: Structure-property relationship of perylene bisimide macrocycles probed by atomic force microscopy and single-molecule fluorescence spectroscopy.
abstract: Properties of a series of acetylene-linked perylene bisimide (PBI) macrocycles with different ring size composed of three to six PBI dyes were investigated by atomic force microscopy (AFM) and single-molecule fluorescence spectroscopy in a condensed phase. It was demonstrated that the structures of PBI cyclic arrays (CNs, N = 3, 4, 5, and 6) become distorted with increasing the ring size through molecular dynamics (MD) simulations (PM6-DH2 method) and AFM height images of CNs on highly ordered pyrolytic graphite (HOPG) surface. The MD simulations showed that only C5 and C6 rings are highly flexible molecules whose planarization goes along with a significant energetic penalty. Accordingly, both molecules did not show ordered adlayers on a HOPG surface. In contrast, C3 and C4 are far more rigid molecules leading to well-ordered hexagonal (C3) and rectangular (C4) 2D lattices. At the single-molecule level, we showed that the fluorescence properties of single CNs are affected by the structural changes. The fluorescence lifetimes of CNs became shorter and their distributions became broader due to the structural distortions with increasing the ring size. Furthermore, the CNs of smaller ring size exhibit a higher photostability and an efficient excitation energy transfer (EET) due to the more well-defined and planar structures compared to the larger CNs. Consequently, these observations provide evidence that not only PBI macrocycles are promising candidates for artificial light-harvesting systems, but also the photophysical properties of CNs are strongly related to the structural rigidity of CNs.
authors: Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University, Seoul, 120-749, Korea.
authors: Ji-Eun
authors: JE
authors: Lee
authors: Vladimir
authors: V
authors: Stepanenko
authors: Jaesung
authors: J
authors: Yang
authors: Hyejin
authors: H
authors: Yoo
authors: Felix
authors: F
authors: Schlosser
authors: Daniel
authors: D
authors: Bellinger
authors: Bernd
authors: B
authors: Engels
authors: Ivan G
authors: IG
authors: Scheblykin
authors: Frank
authors: F
authors: Würthner
authors: Dongho
authors: D
authors: Kim