posted on 2012-07-19, 00:00authored byJunhui Liu, Guofeng Li, Yuanxu Wang
Small three-photon absorption (3PA) cross-section values
of present
nonlinear organic molecules limit their practical applications. Although
electron donors and electron acceptors have a great effect on 3PA
cross-section, little is known about how the strength and situation
of electron acceptors influence the 3PA cross-section value of a compound.
The present work reports 3PA effects of two fluorene derivatives with
symmetric D-π-π(A)-π-D archetype, which are named
as 2,7-bis(4-methoxyphenylacetylene)-9-fluorenone (FATT) and 2,7-bis(4-methoxyphenylacetylene)-9-thoine-fluorene
(TSATL). Large 3PA cross-section and ideal 3PA-induced optical limiting
effects have been found in the two fluorene derivatives. The two molecules
both have a different electron acceptor on the fluorene core, by which
the 3PA cross-section value for FATT is enhanced by nearly 3-fold
compared with that for TSATL. The mechanism of this significant enhancement
in 3PA cross-section has been investigated by density functional theory
(DFT) and configuration interaction singles (CIS) method with use
of 6-311+G basis set in combination with conductor polarizable continuum
model (CPCM). The theoretical results show that increase of electronegative
character of the electron acceptor on the core is responsible for
the increase of 3PA cross-section values of the two molecules.