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).
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.
Ahn
Tae Kyu
TK
Center for Ultrafast Optical Characteristics Control and Department of Chemistry, Yonsei University, Seoul 120-749, Korea.
Kwon
Jung Ho
JH
Kim
Deok Yun
DY
Cho
Dae Won
DW
Jeong
Dae Hong
DH
Kim
Seong Keun
SK
Suzuki
Masaaki
M
Shimizu
Soji
S
Osuka
Atsuhiro
A
Kim
Dongho
D
D000042:Absorption; D015394:Molecular Structure; D010777:Photochemistry; D017785:Photons; D011166:Porphyrins / Q000737:chemistry*; D013816:Thermodynamics; D013997:Time Factors
D011166:Porphyrins