Scheme 1 Schematic representation of nonequilibrium assembly regulated by a time-programmed proton reservoir. Addition of EDCI (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride) promotes ester formation between the bound acid and a hydroxyl compound, thereby temporarily masking the acid as a hydrolysable ester, promoting assembly of compound 1 and activating catalysis of nucleophilic substitution. Subsequent ester hydrolysis regenerates the acid, disrupts the assembly, and returns compound 1 to the monomeric state, while the accompanying pronounced fluorescence changes enable visual monitoring of the process.#

Fig.1 (a) Schematic representation of the self-assembling behavior of compound 1. (b) 1H NMR spectra of 1 mM compound 1 in CDCl3 (green line) and deuterium oxide (D2O, red line). (c) DLS data of compound 1 in an aqueous solution (25°C, 0.01 mM). The insets in (c) show the TEM image and photo of compound 1 aqueous solutions with laser irradiation. (d) UV–vis spectra of 10 µM compound 1 in various solvents. (e) Fluorescence spectra of compound 1 in CH2Cl2 (black line) and water (green line), with λ ex = 360 nm. The inset in (e) shows time-resolved fluorescence decay curves of 10 µM compound 1 in two solvents. (f) Fluorescence spectra of compound 1 in water with different concentrations (1.1–2.5 µM, λ ex = 360 nm). The inset in (f) shows the fluorescence photographs of compound 1 (1 and 10 µM) in water under 365 nm light irradiation. (g) Fluorescence intensity500 nm–concentration curves of compound 1.#

基于吡啶基团的酸碱响应特性，研究人员进一步探索了pH值对组装行为与发光特性的调控作用。如图2所示，随着酸的加入，吡啶基团发生质子化，分子间的堆积作用被破坏，导致纳米组装体解聚为单体。在此过程中，溶液发光颜色由绿光逐渐转变为黄光，光谱峰值红移至570纳米，荧光量子产率降至1.7%。值得注意的是，在中间酸度条件下系统展现出纯正的白光发射，完成了蓝、绿、白、黄的连续光谱演变。对比实验表明，邻位与间位吡啶取代物以及噻吩衍生控制分子均无法实现如此显著的荧光变色效应，证实了对位吡啶结构在构建可视化探针中的关键作用。

Fig.2 (a) Schematic representation of the acid–base responsive behavior of compound 1. The addition of acid causes disassembly and fluorescence yellowing. (b) 1H NMR spectra of 1 mM compound 1 added to acid in deuterium oxide. Changes in (c) UV–vis absorbance, (d) fluorescence spectra, and (e) CIE 1931 chromaticity coordinates of compound 1 in H2O (5 µM) upon acid titration (pH = 3.0∼7.0). (f) Fluorescence photographs of compound 1 aqueous solutions with different pH values under 365 nm light irradiation. (g) Fluorescence photographs of compound 1 loaded on silica gel before treatment (left), after water addition (middle), and after acid addition (right) under 365 nm UV irradiation.#

为了实现非平衡状态的动态调控，研究团队构建了基于碳二亚胺（EDCI）驱动的时间可编程质子水库系统。如图3所示，体系引入三氟乙酸作为酸源，EDCI促使酸与羟基化合物反应生成活化酯，将游离质子临时储存于酯键中。这一过程消耗了体系中的酸，促使溶液pH值升高，进而诱导荧光分子重新组装并发出绿光。随后，活化酯在水相中自发发生水解反应，重新释放出三氟乙酸，使荧光分子再次质子化并解聚，发光颜色恢复为初始的黄光。整个过程无需改动发光分子结构，仅依靠质子水库的酸度变化即可精准操纵超分子组装形态的形成与消失。

Fig.3 (a) Schematic representation of proton reservoir-regulated nonequilibrium assembly. Transient assemblies can be used for catalyzing the nucleophilic substitution reaction. (b) Evolution of the 1H NMR spectra of 1 mM compound 1 added to 1 mM TFA, 1 mM p-nitrophenol, and 3 mM EDCI in deuterium oxide. (c) Evolution of the fluorescence of 0.3 mM compound 1 in water with the addition of 1 mM TFA, 1 mM p-nitrophenol, and 1 mM EDCI (λ ex = 360 nm). (d) Changes in CIE 1931 chromaticity of the fluorescence in (c). (e) Normalized time-dependent profiles derived from fluorescence intensity at 500 nm, UPLC peak areas, and 1H NMR signals for an aqueous solution of compound 1 (1 mM) after addition of TFA (1 mM), p-nitrophenol (1 mM), and EDCI (5 mM). Time-dependent fluorescence intensity at 500 nm of aqueous solutions of compound 1 (0.3 mM) containing TFA (1 mM) and either (f) p-nitrophenol (1 mM) or (g) NHPI (1 mM) upon addition of different equivalents of EDCI (1 equiv. corresponds to 1 mM EDCI, λ ex = 360 nm). (h) Productivity-time curves from UPLC of aqueous solutions (compound 1: 1 mM, TFA: 1 mM, p-nitrophenol: 1 mM, EDCI: 3 mM, blank: 0.1 mM NBD-Cl and 0.14 mM C8-SH).#

研究团队通过分子结构设计实现了对质子水库动力学参数的调控。如图3所示，选用对硝基苯酚作为羟基组件时，生成的活化酯极其稳定，掩蔽酸的时间超过250分钟，可实现酸的长时间稳定储存。换用N-羟基邻苯二甲酰亚胺时，活化酯迅速水解，在30至40分钟内即完成质子释放与组装体的解聚。以五氟苯酚为底物时，系统呈现出平衡的动力学过程，酸掩蔽维持30分钟后，在120分钟内缓释质子。荧光信号的强度变化与核磁共振及超高效液相色谱测得的化学反应动力学曲线高度吻合，证明荧光信号可以作为内部实时指示剂。此外，该组装体展现出优异的催化性能，在4-氯-7-硝基苯并氧杂二唑与正辛硫醇的亲核取代反应中，组装体形成的微环境将反应产率由无催化对照组的17%显著提升至70%。