title: A p-quinodimethane-bridged porphyrin dimer.
abstract: A p-quinodimethane (p-QDM)-bridged porphyrin dimer 1 has been prepared for the first time. An unexpected Michael addition reaction took place when we attempted to synthesize compound 1 by reaction of the cross-conjugated keto-linked porphyrin dimers 8a and 8b with alkynyl/aryl Grignard reagents. Alternatively, compound 1 could be successfully prepared by intramolecular Friedel-Crafts alkylation of the diol-linked porphyrin dimer 14 with concomitant oxidation in air. Compound 1 shows intense one-photon absorption (OPA, λ(max)=955 nm, ε=45400 M(-1) cm(-1)) and a large two-photon absorption (TPA) cross-section (σ((2))(max)=2080 GM at 1800 nm) in the near-infrared (NIR) region due to its extended π-conjugation and quinoidal character. It also exhibits a short singlet excited-state lifetime of 25 ps. The cyclic voltammogram of 1 displays multiple redox waves with a small electrochemical energy gap of 0.86 eV. The ground-state geometry, electronic structure, and optical properties of 1 have been further studied by density functional theory (DFT) calculations and compared with those of the keto-linked dimer 8b. This research has revealed that incorporation of a p-QDM unit into the porphyrin framework had a significant impact on its optical and electronic properties, leading to a novel NIR OPA and TPA chromophore.
authors.affiliation: Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 (Singapore), Fax: (+65) 6779-1691.
authors.forename: Wangdong
authors.initials: W
authors.lastname: Zeng
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Ishida
authors.forename: Sangsu
authors.initials: S
authors.lastname: Lee
authors.forename: Young Mo
authors.initials: YM
authors.lastname: Sung
authors.forename: Zebing
authors.initials: Z
authors.lastname: Zeng
authors.forename: Yong
authors.initials: Y
authors.lastname: Ni
authors.forename: Chunyan
authors.initials: C
authors.lastname: Chi
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
authors.forename: Jishan
authors.initials: J
authors.lastname: Wu
keywords: chromophores; nearinfrared; polycyclic hydrocarbons; porphyrinoids; quinodimethane