Design, Synthesis, and Structural and Spectroscopic Studies of Push–Pull Two-Photon Absorbing Chromophores with Acceptor Groups of Varying Strength

A new series of unsymmetrical diphenylaminofluorene-based chromophores with various strong π-electron acceptors were synthesized and fully characterized. The systematic alteration of the structural design facilitated the investigation of effects such as molecular symmetry and strength of electron-donating and/or -withdrawing termini have on optical nonlinearity. In order to determine the electronic and geometrical properties of the novel compounds, a thorough investigation was carried out by a combination of linear and nonlinear spectroscopic techniques, single-crystal X-ray diffraction, and quantum chemical calculations. Finally, on the basis of two-photon absorption (2PA) cross sections, the general trend for π-electron accepting ability, i.e., ability to accept charge transfer from diphenylamine was: 2-pyran-4-ylidene malononitrile (pyranone) > dicyanovinyl > bis­(dicyanomethylidene)­indane >1-(thiophen-2-yl)­propenone > dicyanoethylenyl >3-(thiophen-2-yl)­propenone. An analogue with the 2-pyran-4-ylidene malononitrile acceptor group exhibited a nearly 3-fold enhancement of the 2PA cross section (1650 GM at 840 nm), relative to other members of the series.本研究合成并全面表征了一系列基于非对称二苯胺基芴的新型生色团（chromophore），其搭载多种强π电子受体。通过系统性调整结构设计，本研究得以深入探究分子对称性、给/吸电子端基强度等因素对光学非线性的影响。为明确该系列新型化合物的电子与几何结构特性，本研究结合线性与非线性光谱技术、单晶X射线衍射及量子化学计算手段开展了全面系统的分析。最终，基于双光子吸收（two-photon absorption, 2PA）截面数据，各π电子受体的电荷接受能力（即接受来自二苯胺的电荷转移的能力）呈现如下递变规律：2-吡喃-4-亚基丙二腈（吡喃酮，pyranone）> 二氰乙烯基 > 双(二氰亚甲基)茚满 > 1-(噻吩-2-基)丙烯酮 > 二氰亚乙基 > 3-(噻吩-2-基)丙烯酮。与该系列其他成员相比，搭载2-吡喃-4-亚基丙二腈受体基团的衍生物，其双光子吸收截面提升近3倍（840 nm下为1650 GM）。