title: Ortho-branched ladder-type oligophenylenes with two-dimensionally π-conjugated electronic properties.
abstract: The synthesis, photochemical and electrochemical properties, and electronic structures of a series of star-shaped ladder-type oligophenylenes Sn (n = 7, 10, 13, 16, 19, and 22), including one multibranched case S19mb, are reported and compared with the linear para-phenylene ladders Rn (n = 2-5 and 8) and the stepladder analogues SFn (n = 10, 16, and 22). The n value refers to the number of π-conjugated phenylene rings. Functionalized isotruxenes are the key synthetic building blocks, and S22 is the largest monodispersed ladder-type oligophenylene known to date. The Sn systems possess the structural rigidity of Rn and the ortho-para phenylene connectivity of SFn. Consequently, Sn represents the first class of branched chromophores with fully two-dimensional conjugation in both ground- and excited-state configurations. Evidences include the excellent linear correlations for the optical 0-0 energies or the first oxidation potentials of Sn and Rn against the reciprocal of their n values, delocalized HOMO and LUMO based on density functional theory calculations, and molecule-like fluorescence anisotropy. The resulting model of effective conjugation plane (ECP) for the two-dimensional π-conjugated systems compliments the concept of effective conjugation length (ECL) for one-dimensional oligomeric systems. Other implications of the observed structure-property relationships are also included.
authors.affiliation: Department of Chemistry, National Taiwan University, Taipei, 10617 Taiwan.
authors.forename: Hsin-Hau
authors.initials: HH
authors.lastname: Huang
authors.forename: Ch
authors.initials: Ch
authors.lastname: Prabhakar
authors.forename: Kuo-Chun
authors.initials: KC
authors.lastname: Tang
authors.forename: Pi-Tai
authors.initials: PT
authors.lastname: Chou
authors.forename: Guan-Jhih
authors.initials: GJ
authors.lastname: Huang
authors.forename: Jye-Shane
authors.initials: JS
authors.lastname: Yang