Fluolab【Angew.Chem.】四川大学谭光映、游劲松|快速可见光聚合反应！全新多通道空间电荷转移光敏剂助力高精度3D打印
文章标题：Multichannel Through‐Space Charge Transfer Triplet Photosensitizers for Rapid Visible‐Light Polymerization and High‐Fidelity 3D Printing
通讯作者：Jingsong You, Guangying Tan
文章概要
引言
可见光驱动的光聚合技术因其出色的时空控制能力和高能量效率，在精密制造和生物医学领域展现出巨大的应用潜力。然而，光敏剂的激发态动力学性质一直制约着该技术的实际表现。为了显著提高聚合动力学并减少加工时间，理想的光敏剂需要同时具备高系间窜越量子产率、长激发态寿命以及极小的单线态-三线态能隙。传统的分子设计主要依赖引入重原子来增强自旋-轨道耦合，但这往往伴随着高昂的合成成本、潜在的生物毒性和较差的光稳定性。尽管近年来发展的基于自旋-轨道电荷转移引发系间窜越的无重原子有机光敏剂备受关注，但传统的通过键电荷转移分子在延长激发态寿命和保持高三线态能量之间存在着难以调和的权衡关系。为了打破这一瓶颈，研究人员开始尝试将空间电荷转移引入分子设计中，但此前报道的单通道空间电荷转移系统普遍存在可见光吸收不足和能隙偏大的问题。基于此，本研究提出了一种全新的邻位多供体-受体（ortho-D3-A）结构设计方案，通过构建三维空间电荷转移网络，成功在一幅分子蓝图中攻克了上述 photophysical 挑战。
(A) Comparison of photosensitizer design. Left: previously reported V-shaped single-channel through-space charge transfer (TSCT) photosensitizers for UV-light-induced polymerization. Right: the ortho-positioned, multi-donor‑acceptor (ortho‑D3‑A) molecule with multichannel TSCT developed in this work. (B) Application demonstration. Schematic illustration of the resin composition and the digital light processing (DLP) 3D printing.
主要实验及结论
研究团队以商用原料为起点，通过简单高效的两步反应成功合成了五种具有多通道空间电荷转移特征的目标分子。单晶X射线衍射结构分析表明，这些分子展现出高度扭曲的三维几何构型，供体与受体之间存在着紧密的平面空间堆叠，这种独特的结构为其高效的空间电子耦合奠定了基础。定量理论计算进一步证实，空间电荷转移对整体电荷转移跃迁的贡献率高达百分之八十九到百分之九十七，占据了绝对主导地位。
(A) Synthesis of the five target TSCT molecules, 3CzTF, 3PhTF, 3_t_BuCzTF, 3DPTF, and 3PNTF. Reaction conditions: Step 1: 2-fluoro-5-(trifluoromethyl)benzonitrile (1, 1.0 equiv.), TfOH (2.25 equiv.) at room temperature for 24 h. Step 2: product 2 (1.0 equiv.), carbazoles or Ar2NH (3.0 equiv.), and NaH (9.0 equiv.) in DMF or THF at room temperature or 80°C for 12 h. (B) Single x-ray structure of 3CzTF. (C) Reduced density gradient (RDG) scatter diagram of 3CzTF. (D) RDG isosurface maps of 3CzTF. (E) Single x-ray structure of 3DPTF. (F) RDG scatter diagram of 3DPTF. (G) RDG isosurface maps of 3DPTF. (H) The interaction ratio of the through-bond and through-space charge transfer transition of the five TSCT molecules.
(A) UV–vis absorption spectra of the five TSCT molecules in toluene (1.0 × 10−5 M). (B) Delayed PL decays of the five TSCT molecules measured in doped films (1 wt% in poly(methyl methacrylate), PMMA). (C) Radar diagram showing the ISC rate constants (_k_ISC) of the five TSCT molecules. (D) Radar diagram showing the radiative decay rate constants (_k_r) of the five TSCT molecules. (E) Radar diagram showing the intersystem crossing quantum yield (_Φ_ISC) of the five TSCT molecules. (F) Energy level diagram of B3LYP/6-31G(d)-calculated excited states of 3CzTF. (G) Energy level diagram of B3LYP/6-31G(d)-calculated excited states of 3DPTF.
在光物理性能测试中，这五个分子在可见光区均表现出高摩尔吸光系数，最大吸收峰位于四百到四百三十纳米之间，且展现出明显的溶剂化显色效应。得益于前沿轨道的高度空间分离，分子的单三线态能隙被压缩至极低的水平，最低仅为0.008电子伏特。时间分辨光致发光光谱显示，这些分子具备微秒级的延迟荧光寿命，意味着产生了长寿命的三线态激子。动力学分析与密度功能理论计算表明，高密度的单三线态耦合能级和强大的自旋轨道耦合常数相互协同，使其中表现最突出的分子实现了高达0.86的系间窜越量子产率。
(A) Synthesis of diphenylketone benzoate oxime ester coinitiators (DPBO1-5) and their key parameters including N–O bond dissociation energies, excited state energy, and enthalpy changes for bond cleavage in both singlet and triplet states. (B) Optimized cluster of a photosensitizer (3CzTF) surrounded by three coinitiators (DPBO-1). (C) HOMO orbital of the optimized cluster. (D) LUMO orbital of the optimized cluster. (E) Electron density map of the optimized cluster. (F) A plausible reaction mechanism for the sensitization of DPBO-1 by 3CzTF.
在应用层面，研究团队将其与新型的二苯基甲酮苯甲酰氧基酯类共引发剂结合。理论与实验研究共同表明，光敏剂在可见光照射下跃迁至激发态后，通过Dexter能量转移机制高效激发共引发剂，引发N-O键的均裂并释放二氧化碳，从而产生能够诱导聚合的活性自由基。实时红外光谱监测显示，在四十毫瓦每平方厘米的四百零五纳米可见光照射下，该两组分引发系统表现出极为优异的引发效率，在空气环境中仅需六十秒照射，单体转化率即可高达百分之七十六，且系统展现出卓越的光开关时空可控性和良好的氧气耐受性。
(A) Schematic illustration of the ATR-IR setup and the corresponding polymerization system. (B) Polymerization kinetic curves (monomer conversion versus irradiation time) of the five TSCT photosensitizer/DPBO-1 systems under 405 nm irradiation (20 mW·cm−2) over 600 s. Photosensitizer concentration: 1.12 × 10−2 mol·L−1; DPBO-1: 2.24 × 10−2 mol·L−1. (C) Polymerization kinetic curves of the five 3CzTF/DPBOs systems under 405 nm irradiation (20 mW·cm−2) over 600 s. (D) Polymerization kinetic curves of the five 3CzTF/DPBOs systems under 455 nm irradiation (20 mW·cm−2) over 600 s. (E) Bar chart showing monomer conversion at 60 s for the five TSCT photosensitizer/DPBO-1 systems under 405 nm irradiation and data were shown from three independent experiments (n = 3). (F) Bar chart for the five 3CzTF/DPBOs systems under 405 nm irradiation and data were shown from three independent experiments (n = 3). (G) Bar chart for the five 3CzTF/DPBOs systems under 455 nm irradiation and data were shown from three independent experiments (n = 3).
鉴于其出色的聚合速率和时空精度，该引发系统被进一步应用于数字光处理（DLP）3D打印中。在无需惰性气体保护的常规空气环境下，利用商业3D打印机成功实现了微米级层厚的高精度连续打印。无论是具有精细线条阵列的基准测试模型，还是复杂的“TSCT”立体三维文字，亦或是具有复杂曲面的中空晶格单元和花朵模型，打印出的成品均展现出极高的几何保真度和优异的层间粘合力。扫描电镜表征证实其打印分辨率完全符合预期，且在紫外灯照射下，成品结构由于内部光敏剂的稳定性而均匀散发出耀眼的翡翠绿荧光。此外，细胞毒性评估结果显示，核心组分在特定浓度下依然能使相关细胞保持百分之八十以上的超高存活率，证明了其出色的生物相容性。
(A) Schematic illustration of DLP 3D printer and the corresponding resin components. (B) Test model incorporating square apertures of various sizes and line arrays of multiple widths and photograph of the printed structure. (C) Photograph of the printed “TSCT” characters and the corresponding SEM image. (D) Photograph of the printed hollow lattice unit model and the corresponding photoluminescent pattern under 365 nm LED irradiation. (E) Printed flower model and the corresponding photoluminescent pattern under 365 nm LED irradiation. Printing conditions: _λ_max = 405 nm, light intensity = 4.0 mW cm−2, layer thickness = 50 µm, and exposure time per layer = 15 s.
总结及展望
这项研究成功开发出了一类基于多通道空间电荷转移机制的全新纯有机无重原子三线态光敏剂分子平台。该设计巧妙地利用高度扭曲的三维空间电荷转移网络，彻底颠覆了系间窜越效率、激发态寿命与能隙大小三者不可兼得的传统认知，实现了各项光物理参数的完美平衡。该系统不仅在可见光诱导的精密自由基光聚合中展现出极高的动力学活性和时空控制力，更在高分辨率DLP 3D打印和生物相容性制造中实现了突破性的应用。这一成果不仅极大地拓宽了无重原子有机光敏剂的分子设计范式，也为下一代精密光学制造和功能材料的开发量身定制了高效、绿色、安全的高性能可见光引发方案。