title: Highly pure synthesis, spectral assignments, and two-photon properties of cruciform porphyrin pentamers fused with benzene units.
abstract: Tetrameric porphyrin formation of 2-hydroxymethylpyrrole fused with porphyrins through a bicyclo[2.2.2]octadiene unit gave bicyclo[2.2.2]octadiene-fused porphyrin pentamers. Thermal conversion of the pentamers gave fully pi-conjugated cruciform porphyrin pentamers fused with benzene units in quantitative yields. UV/Vis spectra of fully pi-conjugated porphyrin pentamers showed one very strong Q absorption and were quite different from those of usual porphyrins. From TD-DFT calculations, the HOMO level is 0.49 eV higher than the HOMO-1 level. The LUMO and LUMO+1 levels are very close and are lower by more than 0.27 eV than those of other unoccupied MOs. The strong Q absorption was interpreted as two mutually orthogonal single-electron transitions (683 nm: 86 %, HOMO-->LUMO; 680 nm: 86 %, HOMO-->LUMO+1). The two-photon absorption (TPA) cross section value (sigma((2))) of the benzene-fused porphyrin pentamer was estimated to be 3900 GM at 1500 nm, which is strongly correlated with a cruciform molecular structure with multidirectional pi-conjugation pathways.
authors.affiliation: Department of Chemistry and Biology, Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Uoyama
authors.forename: Kil Suk
authors.initials: KS
authors.lastname: Kim
authors.forename: Kenji
authors.initials: K
authors.lastname: Kuroki
authors.forename: Jae-Yoon
authors.initials: JY
authors.lastname: Shin
authors.forename: Toshi
authors.initials: T
authors.lastname: Nagata
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Okujima
authors.forename: Hiroko
authors.initials: H
authors.lastname: Yamada
authors.forename: Noboru
authors.initials: N
authors.lastname: Ono
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
authors.forename: Hidemitsu
authors.initials: H
authors.lastname: Uno