title: Three-photon absorption cross-section enhancement in two symmetrical fluorene-based molecules.
abstract: In this article, we report the pure three-photon absorption effects of two novel symmetrical fluorene-based molecules with 2D-pi-2D [9,9-diethylhexyl-2,7-bis-(N,N-diphenylamine)fluorene] and 2D-D-pi-D-2D [5,5'-(9,9-bis-(2-ethylhexyl)-9H-fluorene-2-yl)bis(N,N-diphenylthiophen-2-amine)] structural motifs. The obtained three-photon absorption cross sections, (4.74 +/- 0.01) x 10(-76) and (6.77 +/- 0.02) x 10(-76) cm(6) s(2) for the 2D-pi-2D and 2D-D-pi-D-2D archetypes, respectively, are rather high. The geometries and electronic excitations of the two molecules were systematically studied by the PM3 and ZINDO/S methods. The influence of the different molecular structures on the three-photon absorption cross section is discussed micromechanically. The experimental and theoretical results demonstrate that the transition dipole moment between the ground and final states is the most definitive factor. A new fitting method that is more accurate than those reported previously was used to obtain the 3PA coefficient.
authors.affiliation: Institute of Microsystem of Physics, Department of Physics and Electronics, Henan University, Kaifeng, Henan 475001, P. R. China. junhuiliu@henu.edu.cn
authors.forename: Junhui
authors.initials: J
authors.lastname: Liu
authors.forename: Yanli
authors.initials: Y
authors.lastname: Mao
authors.forename: Mingju
authors.initials: M
authors.lastname: Huang
authors.forename: Yuzong
authors.initials: Y
authors.lastname: Gu
authors.forename: Weifeng
authors.initials: W
authors.lastname: Zhang