title: Comparative photophysical properties of free-base, bis-Zn(II), bis-Cu(II), and bis-Co(II) doubly N-confused hexaphyrins(1.1.1.1.1.1).
abstract: We have comparatively investigated the photophysics of a series of bis-metal doubly N-confused hexaphyrins(1.1.1.1.1.1) using time-resolved fluorescence, femtosecond transient absorption, two-photon absorption measurements, and geometry-optimized ab initio calculations. Bis-Zn(II) and free-base doubly N-confused hexaphyrins exhibit well-resolved and red-shifted B- and Q-like absorption bands compared with porphyrins. Their allowed transitions are (pi,pi) transitions of the hexaphyrin ring, as confirmed by the HOMO and LUMO frontier orbitals based on ab initio calculations at the B3LYP/6-31G level. On the other hand, the absorption spectra of bis-Cu(II) and bis-Co(II) doubly N-confused hexaphyrins are relatively broad, presumably due to large couplings between the metal d-orbitals and pi-electrons of the hexaphyrin ring. Owing to these couplings, bis-Cu(II) and bis-Co(II) doubly N-confused hexaphyrins have much shorter excited-state lifetimes of 9.4 +/- 0.3 ps and 670 fs, respectively, than those (267 +/- 16 and 62.4 +/- 1.2 ps, respectively) of bis-Zn(II) and free-base doubly N-confused hexaphyrins. The two-photon absorption cross section (sigma(2)) values, which are believed to depend strongly on the ring planarity (pi-conjugation), are in line with the excited-state lifetime trends.
authors.affiliation: Center for Ultrafast Optical Characteristics Control and Department of Chemistry, Yonsei University, Seoul 120-749, Korea.
authors.forename: Jung Ho
authors.initials: JH
authors.lastname: Kwon
authors.forename: Tae Kyu
authors.initials: TK
authors.lastname: Ahn
authors.forename: Min-Chul
authors.initials: MC
authors.lastname: Yoon
authors.forename: Deok Yun
authors.initials: DY
authors.lastname: Kim
authors.forename: Mi Kyoung
authors.initials: MK
authors.lastname: Koh
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Furuta
authors.forename: Masaaki
authors.initials: M
authors.lastname: Suzuki
authors.forename: Atsuhiro
authors.initials: A
authors.lastname: Osuka