Fluolab【Adv.Mater.】郑州大学臧双全等|突破极限！近红外圆偏振发光不对称因子高达-0.4，开启夜视成像新范式
通讯作者： Xi-Yan Dong, Jia-Chen Zhang, Shuang-Quan Zang
文章概要
引言
近红外（NIR）圆偏振发光（CPL）材料在生物成像、光通信及信息加密等领域展现出巨大的应用潜力。然而，如何提升发光不对称因子（） 一直是该领域的核心痛点，现有的近红外CPL系统往往面临手性响应弱、稳定性差以及在固态环境下易发生猝灭等挑战。为了克服这些障碍，研究团队巧妙地提出了一种螺旋光子限制策略。通过将具有优异光物理性能的金纳米团簇（）嵌入到具有手性向列结构的手性介孔二氧化硅（CNMS）薄膜中，利用光子带隙（PBG）与团簇发射光谱的精确匹配，实现了近红外手性发光性能的跨越式提升。
(a) NCs with different sizes and luminescent properties (Cu3, CAu6, CAu6Ag4, Au13). (b) Schematic of NCs loaded onto CNMS films (forming NC-CNMS). (c) Schematic of PBG-induced R-CPL emission from NCs-CNMS. When the emission band of NCs overlaps with the PBG of the CNMS film, the left-handed nematic NCs-CNMS film selectively reflects L-CPL and transmits R-CPL.
主要实验及结论
研究人员首先通过优化蒸发诱导自组装工艺，制备出了具有长程有序螺旋结构的手性介孔二氧化硅薄膜，并通过调节超声处理时间精准调控其光子带隙。实验发现，当二氧化硅薄膜的光子带隙与金纳米团簇的发射峰精准重叠时，复合材料表现出极强的右圆偏振发光（R-CPL）。令人振奋的是，该系统的发光不对称因子达到了-0.4，这一数值远超传统的自由纳米团簇，创造了同类材料的新纪录。这种显著的性能提升并非源于团簇本身的分子手性，而是源于手性光子晶体架构对手性发光路径的强力调制。
(a) Representative SEM image of CNC/SiO2 film and (b) CNMS film. (c) Representative POM image of CNMS. (d,e) TEM and elemental mapping images of Au13-CNMS film. (f) Nitrogen adsorption of CNMS film, (g) XRD pattern of Au13-CNMS, (h) XPS spectrum of Au13-CNMS.
(a) CPL spectra of Au13-CNMS-n films (Au13 solution concentration 3 mg/mL). (b) CPL spectra of CNMS-750 films loaded with different concentrations of Au13 NCs. (c) CPL spectra of CNMS-n films loaded with different clusters. (d) _g_lum values of Au13-CNMS-n. (e) _g_lum values of CNMS-750 films loaded with different concentrations of Au13 NCs. (f) _g_lum values of CNMS-n films loaded with different clusters. (g) Digital images of NCs-CNMS-n under natural light and UV light. (h) Wavelength and helicity modulation of NCs-CNMS-n films. (i) _g_lum of wavelength and helicity modulation in NCs-CNMS-n films.
在深入探索其动态响应特性时，研究团队发现该材料具有独特的溶剂响应开关特性。当水分子渗透进入薄膜孔隙后，由于折射率匹配效应，薄膜的双折射现象被抑制，导致CPL信号暂时熄灭；而在水分挥发过程中，信号随之恢复。特别值得注意的是，在水分蒸发阶段，由于金纳米团簇在螺旋纳米通道内发生了由疏水作用驱动的瞬态自组装，系统甚至出现了短暂的手性反转现象。这一发现不仅通过时间分辨瞬态吸收光谱得到了验证，还为开发响应型光子器件提供了全新的思路。基于这一卓越的光学性能，团队成功构建了一套近红外手性偏振成像系统，在无需外部偏振光学元件的情况下，实现了对近红外光的高对比度直接区分与成像。
(a) Schematic illustration of CPL switching capability achieved by solution permeation and evaporation of NCs-CNMS films. (b) CPL spectra of Au13-CNMS: (light yellow) original film, (pink) film immersed in H2O, and (blue dotted line) subsequent H2O evaporation. (c) CPL intensity of Au13-CNMS after 50 cycles of H2O immersion-evaporation. (d) Dynamic CPL spectrum of Au13-CNMS during water evaporation. (e) Dynamic CPL spectrum of CAu6-CNMS during water evaporation. (f) Two-dimensional TA map recorded using left-circularly polarized (L) probe light (dry film). (g) Two-dimensional TA map recorded using right-circularly polarized (R) probe light (dry film). (h) Corresponding differential (L–R) transient absorption spectrum (dry film). (i) Two-dimensional TA map recorded with left-circularly polarized (L) probe light (wet film). (j) Two-dimensional TA map recorded with right-circularly polarized (R) probe light (wet film). (k) Corresponding differential (L–R) transient absorption spectrum (wet film, Circular dichroism TA spectra of Au13-CNMS films were recorded under 350 nm excitation).
(a) Schematic Au13-CNMS assembly during solvent evaporation. (b) shows the stacking arrangement of Au13 clusters in the single crystal as viewed along the b-axis; (c) View along the c-axis showing the spatial distribution of Au13 clusters within the single crystal and their weak intercluster interactions, together with the corresponding crystal photograph. (d) SEM image of Au13 NCs in DMF solution. (e) SEM image of Au13 cluster in DMF: H2O = 1:9 (v/v) solution. f) SEM image of Au13 NCs in DMF: H2O = 1:9 (v/v) solution after freeze-drying.
(a) Difference in near-infrared luminescence intensity of Au13-CNMS under L-CPF and R-CPF circular polarization. (b) Near-infrared imaging: Visible light imaging under natural light (left) and near-infrared camera imaging under Au13-CNMS luminescence (right). (c) Schematic of near-infrared chiral polarization imaging principle: Incident light is converted into near-infrared emission by the Au13-CNMS film after passing through the sample and is captured by the camera. (d) Comparison of near-infrared images acquired via L-CPF and R-CPF, demonstrating significant chiral selectivity and high contrast. (e) Near-infrared imaging sequence obtained by continuously rotating the circularly polarized filter angle, validating a highly sensitive and stable response to circularly polarized states.
总结及展望
该研究成功建立了一种普适性的螺旋光子限制策略，不仅在近红外波段实现了创纪录的手性放大，还将这一体系扩展至蓝、绿、橙等全可见光波段。通过揭示水诱导的团簇动态组装规律，研究进一步深化了对手性光子材料结构与性能关系的理解。这项工作为开发高性能、可调控、方向敏感的近红外手性光电材料奠定了坚实基础，并在隐蔽光通信、高安全性防伪和新一代功能化光子器件领域展现出极其广阔的应用前景。