Institute for Computational Materials Science, Department of Physics, Henan University, Kaifeng 475001, Peoples Republic of China.
J Phys Chem A. 2012 Jul 19;116(28):7445-51. doi: 10.1021/jp301657g. Epub 2012 Jul 5.
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.
目前非线性有机分子的小三光子吸收（3PA）截面值限制了它们的实际应用。尽管电子给体和电子受体对 3PA 截面有很大的影响，但对于电子受体的强度和情况如何影响化合物的 3PA 截面值，人们知之甚少。本工作报道了两种具有对称 D-π-π(A)-π-D 原型的芴衍生物的 3PA 效应，它们分别命名为 2,7-双（4-甲氧基苯乙炔基）-9-芴酮（FATT）和 2,7-双（4-甲氧基苯乙炔基）-9-噻吩芴（TSATL）。在这两种芴衍生物中发现了大的 3PA 截面和理想的 3PA 诱导光限幅效应。这两个分子在芴核上都有一个不同的电子受体，通过这种方式，FATT 的 3PA 截面值比 TSATL 增强了近 3 倍。通过密度泛函理论（DFT）和组态相互作用单（CIS）方法，并结合导体极化连续模型（CPCM），使用 6-311+G 基组，研究了这种 3PA 截面显著增强的机制。理论结果表明，核心上电子受体的电负性增加是导致两个分子 3PA 截面值增加的原因。
