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首页> 外文期刊>Chemistry: A European journal >Experimental and theoretical studies on organic D-π-a systems containing three-coordinate boron moieties as both π-donor and π-acceptor
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Experimental and theoretical studies on organic D-π-a systems containing three-coordinate boron moieties as both π-donor and π-acceptor

机译：含三配位硼原子作为π供体和π受体的有机D-π-a体系的实验和理论研究

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Four linear p-conjugated systems with 1,3-diethyl-1,3,2-benzodiazaborolyl [C _6H _4(NEt) _2B] as a p-donor at one end and dimesitylboryl (BMes _2) as a p-acceptor at the other end were synthesized. These unusual push-pull systems contain phenylene (-1,4-C _6H _4-; 1), biphenylene (-4,4'-(1,1'-C _6H _4) _2-; 2), thiophene (-2,5-C _4H _2S-; 3), and dithiophene (-5,5'-(2,2'-C _4H _2S) _2-; 4) as p-conjugated bridges and different types of three-coordinate boron moieties serving as both p-donor and p-acceptor. Molecular structures of 2, 3, and 4 were determined by single-crystal X-ray diffraction. Photophysical studies on these systems reveal bluegreen fluorescence in all compounds. The Stokes shifts for 1, 2, and 3 are notably large at 7820-9760 cm ~(-1) in THF and 5430-6210 cm ~(-1) in cyclohexane, whereas the Stokes shift for 4 is significantly smaller at 5510 cm ~(-1) in THF and 2450 cm ~(-1) in cyclohexane. Calculations on model systems 1'-4' show the HOMO to be mainly diazaborolyl in character and the LUMO to be dominated by the empty p orbital at the boron atom of the BMes _2 group. However, there are considerable dithiophene bridge contributions to both orbitals in 4'. From the experimental data and MO calculations, the π-electrondonating strength of the 1,3-diethyl- 1,3,2-benzodiazaborolyl group was found to lie between that of methoxy and dimethylamino groups. TD-DFT calculations on 1'-4', using B3LYP and CAM-B3LYP functionals, provide insight into the absorption and emission processes. B3LYP predicts that both the absorption and emission processes have strong charge-transfer character. CAM-B3LYP which, unlike B3LYP, contains the physics necessary to describe charge-transfer excitations, predicts only a limited amount of charge transfer upon absorption, but somewhat more upon emission. The excitedstate (S _1) geometries show the borolyl group to be significantly altered compared to the ground-state (S _0) geometries. This borolyl group reorganization in the excited state is believed to be responsible for the large Stokes shifts in organic systems containing benzodiazaborolyl groups in these and related compounds.
机译：四个线性p共轭体系，其中1,3-二乙基-1,3,2-苯并二氮杂硼烯丙基[C _6H _4（NEt）_2B]的一端为p-供体，而二聚间苯二甲酰（BMes _2）为p-受体。另一端被合成。这些不寻常的推挽系统包含亚苯基（-1,4-C _6H _4-; 1），亚联苯（-4,4'-（1,1'-C _6H _4）_2-; 2），噻吩（-2 ，5-C _4H _2S- ;; 3）和二噻吩（-5,5'-（2,2'-C _4H _2S）_2-; 4）作为p共轭桥和不同类型的三坐标硼部分作为p-供体和p-受体。通过单晶X射线衍射确定2、3和4的分子结构。在这些系统上的光物理研究表明，所有化合物均具有蓝绿色荧光。 1、2和3的斯托克斯位移明显较大，在THF中为7820-9760 cm〜（-1），在环己烷中为5430-6210 cm〜（-1），而4的斯托克斯位移在5510 cm时明显较小在THF中约为（-1），在环己烷中约为2450 cm（-1）。对模型系统1'-4'的计算表明，HOMO的性质主要为二氮杂硼烯丙基，而LUMO则由BMes _2基团的硼原子处的空p轨道占据主导地位。但是，在4'的两个轨道上都有相当大的二噻吩桥贡献。从实验数据和MO计算，发现1，3-二乙基-1，3，2-苯并二氮杂硼烯丙基的π-电子强度介于甲氧基和二甲基氨基之间。使用B3LYP和CAM-B3LYP功能在1'-4'上进行TD-DFT计算，可以深入了解吸收和发射过程。 B3LYP预测吸收和发射过程都具有很强的电荷转移特性。与B3LYP不同，CAM-B3LYP包含描述电荷转移激发所必需的物理原理，它仅预测吸收后有限数量的电荷转移，但发射时预测更多。与基态（S _0）的几何形状相比，激发态（S _1）的几何形状显示硼烯丙基基团发生了显着变化。据认为，在激发态中这种硼烯丙基的重组是造成这些化合物和相关化合物中含有苯并二氮杂硼烯丙基的有机体系中斯托克斯位移大的原因。

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