Symmetrical and unsymmetrical multibranched D–π–A molecules based on 1,3,5-triazine unit: synthesis and photophysical properties
作者:Liqian Zhang、Li Zou、Jiang Xiao、Pengcheng Zhou、Cheng Zhong、Xingguo Chen、Jingui Qin、Inês F. A. Mariz、Ermelinda Maçôas
DOI:10.1039/c2jm32323k
日期:——
A series of V-shaped (DâÏâAâÏâD) and star-shaped ((DâÏâ)3A) molecules based on the electron acceptor 1,3,5-triazine core (A) connected to different electron donor groups (D) by a carbonâcarbon triple bond as a conjugation bridge (Ï) has been synthesized. The studied molecules can be separated into symmetrically and unsymmetrically substituted molecules depending on the combination of the electron donating branches connected to the triazine core. Their photophysical properties are characterized experimentally and the structureâproperties relationship is analysed with the aid of theoretical calculations. The symmetrically branched 1,3,5-triazine-based molecules exhibit similar UV-vis absorption to the corresponding linear molecules, but an obvious blue-shift in the emission is observed with increasing dimensionality. The absorption of the unsymmetrically branched 1,3,5-triazine-based molecules is clearly localized on a specific branch, suggesting a weak interbranch conjugation in the ground state. Emission is mainly controlled by the branch with the lowest energy excited state, which corresponds to the one with the largest intramolecular charge transfer (ICT) effect. The two-photon absorption properties of selected molecules are studied. They exhibit strong two-photon absorption activities and a modest interbranch conjugation effect, enhancing the TPA cross-section beyond the additive effect of increasing branch number.
一系列基于电子受体1,3,5-三嗪核心(A)的V形(D–π–A–π–D)和星形((D–π–)3A)分子被合成,这些分子通过碳–碳三键作为共轭桥(π)与不同的电子供体基团(D)连接。研究的分子可以根据连接到三嗪核心的电子供体分支的组合分为对称和非对称取代分子。它们的光物理性质通过实验表征,并借助理论计算分析结构–性质关系。对称分支的1,3,5-三嗪基分子在UV-vis吸收方面与相应的线性分子表现相似,但随着维度的增加,发射出现明显的蓝移。非对称分支的1,3,5-三嗪基分子的吸收显著局限于特定分支,表明在基态下分支间的共轭作用较弱。发射主要受到最低能量激发态的分支的控制,而该分支对应于具有最大分子内电荷转移(ICT)效应的分支。对选定分子的双光子吸收特性进行了研究,结果显示它们具有强的双光子吸收活性和适度的分支间共轭效应,使得TPA横截面超过了单纯增加分支数量所带来的累加效应。