点手性调控的三股铕螺旋体的非对映选择性自组装及圆偏振发光

doi:10.6023/A21040185

摘要/Abstract

具有超分子手性的稀土螺旋体为合成高性能稀土圆偏振发光(CPL)材料提供了结构基础. 然而, 稀土Ln(III)离子较大的半径和不稳定的配位几何构型为合成高光学纯度的稀土螺旋体带来了困难和挑战. 本工作通过在双三齿配体端基引入点手性的方式成功构筑了一对儿对映体纯的手性双核三股铕螺旋体, [Eu₂(L^RR)₃](OTf)₆和[Eu₂(L^SS)₃](OTf)₆. 结合全面的光谱表征和半经验分子力学模型证实了配体端基的点手性成功诱导两个稀土Eu³⁺离子采取相同的Λ或Δ构型, 并形成具有单一M或P螺旋构象的螺旋体. 配合物的镜像圆二色(CD)和CPL光谱也进一步验证了一对儿光学纯对映体的形成. 手性光学性质研究显示螺旋体在乙腈中表现出适中的发光不对称因子(|g_lum|=0.083)和良好的发光量子产率(QY=19%). 该方法为制备性能优异的手性稀土CPL材料提供了一种可行性参考.

关键词: 稀土配合物, 手性螺旋体, 手性诱导, 圆偏振发光(CPL)

The supramolecular chirality of lanthanide helicate offers a structural base to synthesize the excellent lanthanide circularly polarized luminescent (CPL) materials. However, the larger radii and the labile coordination geometries of the Ln(III) ions make it difficult to control the diastereoselectivity of lanthanide helicates in the self-assembly process. Herein, a pair of chiral dinuclear europium triple-stranded helicates [Eu₂(L^RR)₃](OTf)₆ and [Eu₂(L^SS)₃](OTf)₆ (L^RR^/^SS=N,Nʹ-(ethane-4,4ʹ-diyl)bis[6-(R/S)-(1-phenethylcarbamoyl)-pyridine-2-dimethylamide]) were synthesized via point chirality induced strategy. The ligands L^RR^/^SS were composed of two chiral 2,6-dipicolinic amides as coordination units and ethylenediamine moieties as spacers. General procedure for the preparation of ligands L^RR^/^SS and corresponding europium complexes [Eu₂(L^RR^/^SS)₃](OTf)₆: 6-(Methoxycarbonyl)picolinic acid 4a (1.50 g, 5.6 mmol) was dissolved in 5 mL SOCl₂ and stirred for 6 h. The white precipitate was obtained after removed SOCl₂, and then it was added to 30 mL CH₂Cl₂ containing 4-dimethylaminopyridine (0.12 g, 1.0 mmol) and triethylamine (0.48 g, 8.0 mmol). Ethylenediamine (0.12 g, 2.0 mmol) in 5 mL CH₂Cl₂ was added by dropwise to the above solution and further stirred for 10 h. After the solution was washed with 1 mol•L^-1 HCl, saturated sodium bicarbonate and water, dried over sodium sulfate, and evaporated to remove solvent. The crude product was purified by crystallization from CH₂Cl₂:n-hexane (V/V=1:20) to give L^RR^/^SS (0.54 g, 47%). L^RR^/^SS (0.10 g, 0.18 mmol) dissolved in 10 mL acetonitrile, Eu(OTf)₃ (0.07 g, 0.12 mmol) in 5 mL acetonitrile was added dropwise to the above solution and stirred for 24 h. After the slow volatilization of reaction solution, the white crystals were obtained, [Eu₂(L^RR^/^SS)₃](OTf)₆ (0.12 g, 71%). Combination of the comprehensive spectral characteristics and semiempirical geometry optimization demonstrated that the point chirality at the terminal of the ligand successfully controlled the Δ or Λ configuration around the metal center and the P or M helical conformation of the helicates. The mirror-image circular dichroism (CD) and CPL spectra further confirmed the formation of the enantiomer pairs. Notably, the helicates exhibit excellent CPL emission with the |g_lum| values reaching to 0.083 and the modest luminescence quantum yields (QYs=19%) in CH₃CN. This study provides an effective strategy for the syntheses of chiral lanthanide CPL materials with excellent performance.

Key words: lanthanide complex, chiral helicate, chiral induction, circularly polarized luminescence (CPL)

引用此文

宋龙飞, 周妍妍, 高婷, 闫鹏飞, 李洪峰. 点手性调控的三股铕螺旋体的非对映选择性自组装及圆偏振发光[J]. 化学学报, 2021, 79(8): 1042-1048.

Longfei Song, Yanyan Zhou, Ting Gao, Pengfei Yan, Hongfeng Li. Point Chirality Regulated Diastereoselective Self-Assembly and Circularly Polarized Luminescence in Eu(III) Triple-Stranded Helicates[J]. Acta Chimica Sinica, 2021, 79(8): 1042-1048.

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图/表 7

图1. 手性配体LRR/SS及其稀土配合物[Ln2(LRR/SS)3](OTf)6的合成路线

Figure 1. Syntheses of the chiral ligands LRR/SS and the corresponding lanthanide complexes [Ln2(LRR/SS)3](OTf)6

图2. (a) [Eu2(LSS)3](OTf)6的ESI-TOF质谱(插图: 实测和模拟的同位素分布). (b) [Y2(LSS)3](OTf)6在CD3CN中的400 MHz 1H NMR. (c) [Y2(LSS)3](OTf)6 在CD3CN中的1H DOSY NMR

Figure 2. (a) ESI-TOF mass spectrum of [Eu2(LSS)3](OTf)6 with insets showing the simulated (Sim.) and observed (Obs.) isotopic pattern. (b) 1H NMR (400 MHz) spectra of free ligand LSS and [Y2(LSS)3](OTf)6 in CD3CN. (c) 1H DOSY NMR spectrum of [Y2(LSS)3](OTf)6 in CD3CN

图3. Sparkle/AM1优化的配合物[Eu2(LRR)3](OTf)6(左)和[Eu2(LSS)3](OTf)6(右)的基态构型

Figure 3. Sparkle/AM1 ground state geometries of the complexes [Eu2(LRR)3](OTf)6 (left) and [Eu2(LSS)3](OTf)6 (right)

图4. (a) 配体LSS在CH3CN (3×10-5 mol•L-1)中的UV-vis光谱随着0~2.0 equiv. Eu(CF3SO3)3 (CH3CN, 3×10-3 mol•L-1)加入的变化. (b) 计算的物种分布图

Figure 4. (a) Variation of the UV-vis spectra of LSS in CH3CN (3×10-5 mol•L-1) upon addition of the Eu(CF3SO3)3 (CH3CN, 3×10-3 mol•L-1) from 0~2.0 equiv. (b) Calculated distribution plots of the species

Species	log β_M/L	% Species for M/[L^SS]	Concentration of Species/(10^-6 mol•L^-1)
log β₂₃	36.600	81.0	0.92
log β₂₂	26.636	9.5	0.11

表1. 通过拟合吸收光谱变化计算的物种累积平衡常数、种类分布以及在[Eu]/[LSS]=0.66时计算的物种浓度

Table 1. Binding constants, species distribution estimated by fitting the changes in absorption spectra, and the calculated species concentration of the complexes with the [Eu]/[LSS]=0.66

图5. (a) 手性配体LRR/SS及稀土螺旋体[Eu2(LRR)3](OTf)6和[Eu2(LSS)3](OTf)6在乙腈中的UV-vis光谱(下)和CD光谱(上) (1.0×10-5 mol•L-1). (b) 手性稀土螺旋体[Eu2(LRR)3](OTf)6和[Eu2(LSS)3](OTf)6在乙腈中的发射光谱(下)和CPL光谱(上) (1.0×10-5 mol•L-1)

Figure 5. (a) UV-vis absorption (lower curves) and CD spectra (upper curves) of the chiral ligands LRR/SS and lanthanide helicates [Eu2(LRR)3](OTf)6 and [Eu2(LSS)3](OTf)6 in CH3CN (1.0×10-5 mol•L-1). (b) Total luminescence (lower curves) and CPL spectra (upper curves) of [Eu2(LRR)3](OTf)6 and [Eu2(LSS)3](OTf)6 in CH3CN (1.0×10-5 mol•L-1)

Complex	k_r/s^-1	k_nr/s^-1	τ_obs/μs	Φ_Eu/%	η_sens/%	Φ_overall/%	g_lum ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4)
Complex	k_r/s^-1	k_nr/s^-1	τ_obs/μs	Φ_Eu/%	η_sens/%	Φ_overall/%	J=0	J=1	J=2	J=3	J=4
Eu₂(L^RR)₃	180	551	1372	24.8	75.0	18.6	–0.002	–0.083	0.026	0.037	0.011
Eu₂(L^SS)₃	184	553	1356	24.9	75.9	18.9	0.002	0.083	–0.024	–0.034	–0.013

表2. 辐射(kr)和非辐射(knr)跃迁的速率常数, 观察的发光寿命(τEu obs), 敏化效率(ηsens), 固有量子产率(ΦEu), 总发光量子产率(Φoverall)和Eu3+离子的5D0→7FJ的glum值a

Table 2. Rate constants of radiative (kr) and nonradiative (knr) decay, observed luminescence lifetime (τEu obs), sensitization efficiency (ηsens), intrinsic quantum yields (ΦEu), overall quantum yield (Φoverall), and glum values for 5D0→7FJ of the Eu3+ ion a

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