Laboratoire de Chimie Moléculaire et Spectroscopies Avancées (LCOSA), ICEEPS-LCOSA, UMR CNRS 7515, École Européenne de Chimie, Polymères et Matériaux (ECPM), 25 rue Becquerel, 67087 Strasbourg Cedex 02, France.
Chemistry. 2013 Apr 22;19(17):5375-86. doi: 10.1002/chem.201203625. Epub 2013 Feb 27.
A series of thirteen luminescent tetrahedral borate complexes based on the 2-(2'-hydroxyphenyl)benzoxazole (HBO) core is presented. Their synthesis includes the incorporation of an ethynyl fragment by Sonogashira cross-coupling reaction, with the goal of extending the conjugation and consequently redshifting their emission wavelength. Different regioisomers, substituted in the 3-, 4-, or 5-position of the phenolate side of the HBO core, were studied in order to compare their photophysical properties. The complexes were characterized by X-ray diffraction and NMR, UV/Vis, and emission spectroscopy in solution and in the solid state. In all cases, complexation to boron leads to a donor-acceptor character that impacts their photophysical properties. Complexes with a 3- or 5-substituted fragment display mild to pronounced internal charge transfer (ICT), a feature strengthened by the presence of p-dibutylaminophenylacetylene in the molecular structure, protonation of the nitrogen atom of which leads to a significant blueshift and an increase in quantum yield. On the contrary, when the ethynyl module is grafted on the 4-position, narrow, structured, symmetrical absorption/emission bands are observed. Moreover, the fact that protonation has little effect on the emission maximum wavelength reveals singlet excited-state decay. Solid-state emission properties reveal a redshift compared to solution, explained by tight packing of the π-conjugated systems and the high planarity of the dyes. Subsequent connection of these complexes to other photoactive subunits (BODIPY, Boranil) provides dyads in which efficient cascade energy transfer is observed.
呈现了一系列基于 2-(2'-羟基苯基)苯并恶唑（HBO）核心的十三种发光四面体硼酸盐配合物。它们的合成包括通过 Sonogashira 交叉偶联反应引入乙炔基片段，目的是延长共轭并因此红移它们的发射波长。研究了不同的区域异构体，它们在 HBO 核心的酚盐侧的 3-、4-或 5-位取代，以比较它们的光物理性质。通过 X 射线衍射和 NMR、UV/Vis 和发射光谱在溶液和固态中对配合物进行了表征。在所有情况下，硼的络合导致供体-受体性质，从而影响它们的光物理性质。具有 3-或 5-取代片段的配合物显示出温和到明显的内部电荷转移（ICT），这一特征通过分子结构中存在对二丁基氨基苯乙炔得到加强，其中氮原子的质子化导致明显的蓝移和量子产率增加。相反，当乙炔基模块接枝在 4-位时，观察到窄、结构化、对称的吸收/发射带。此外，质子化对发射最大波长几乎没有影响，这揭示了单重态激发态衰减。固态发射性质与溶液相比显示出红移，这可以通过π共轭体系的紧密堆积和染料的高平面性来解释。随后将这些配合物连接到其他光活性亚基（BODIPY、Boranil）上，提供了观察到有效级联能量转移的二聚体。
