title: Comparative photophysics of [26]- and [28]hexaphyrins(1.1.1.1.1.1): large two-photon absorption cross section of aromatic [26]hexaphyrins(1.1.1.1.1.1).
abstract: We have explored the electronic natures of representative expanded porphyrins, [26]- and [28]hexaphyrins, to investigate the interplay between the aromaticity and antiaromaticity that is brought by two electron oxidation/reduction processes. The excited singlet and triplet states of [26]hexaphyrin in solution exhibit lifetimes of 125 ps and 1.8 mus, respectively, as revealed by various time-resolved spectroscopic measurements. On the other hand, [28]hexaphyrin shows faster singlet and triplet lifetimes than those of [26]hexaphyrin, which is largely in accordance with the perturbation of aromaticity due to the pi electron formulation of [4n] in [28]hexaphyrins. The two-photon absorption cross-section values at 1200 nm for [26]hexaphyrins show ca. 9890 GM which is >10(2) larger than those of porphyrins. The reduced TPA values of 2600 and 810 GM of [28]hexaphyrin and perfluorinated [28]hexaphyrin, respectively, match well with their relatively short excited-state lifetimes. Overall, the enhanced excited-state lifetimes for various hexaphyrins go in line with the increased TPA cross-section values and the ring planarity.
authors.affiliation: Center for Ultrafast Optical Characteristics Control and Department of Chemistry, Yonsei University, Seoul 120-749, Korea.
authors.forename: Tae Kyu
authors.initials: TK
authors.lastname: Ahn
authors.forename: Jung Ho
authors.initials: JH
authors.lastname: Kwon
authors.forename: Deok Yun
authors.initials: DY
authors.lastname: Kim
authors.forename: Dae Won
authors.initials: DW
authors.lastname: Cho
authors.forename: Dae Hong
authors.initials: DH
authors.lastname: Jeong
authors.forename: Seong Keun
authors.initials: SK
authors.lastname: Kim
authors.forename: Masaaki
authors.initials: M
authors.lastname: Suzuki
authors.forename: Soji
authors.initials: S
authors.lastname: Shimizu
authors.forename: Atsuhiro
authors.initials: A
authors.lastname: Osuka
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
mesh_terms: D000042:Absorption; D015394:Molecular Structure; D010777:Photochemistry; D017785:Photons; D011166:Porphyrins / Q000737:chemistry*; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D011166:Porphyrins