Fig.1 Comparison between conventional photoswitch molecules and steric-hindrance DAEs possessing AIE activity. (a) Structural overview of fluorescent photoswitches, which typically exhibit aggregation-caused quenching. (b) A steric-hindrance photochromic system studied in this work with ultraviolet/visible light activated fluorescence enhancement, exhibiting AIE behaviour. Visible-light-driven photocyclization and redshifted absorption-emission spectrum achieved through electronic effect modulation.#

在溶液态光响应测试中，四种光开关均表现出优异的紫外光致环化性能，环化转化率高达95%以上，其中OS‑2达到97.9%。闭合异构体在室温下放置100小时未见明显衰减，证明其具有良好的热稳定性。静电势分析和前线分子轨道计算表明，给电子能力越强的取代基越能提高分子核心区域的电子云密度，缩小HOMO‑LUMO能隙。实验上，OS‑3和OS‑4的吸收带分别比OS‑2红移了45 nm和73 nm，荧光发射也相应红移。如图2所示，在紫外光照射下，无色溶液逐渐变为黄色并伴随荧光显著增强，OS‑4在溶液中的荧光开/关对比度达到101.6倍，呈现典型的“turn‑on”荧光调制模式。

Fig. 2 Photoresponse and fluorescence behaviour of oxidized DAE based on steric hindrance ethene bridge, with substituents exhibiting different electronic effects. (a) Absorption spectra change of OS 2 upon irradiation with UV light (λ = 313 ± 10 nm). The inset images show the colour changes. (b) Absorption spectrum of o-OS 2 (open-ring isomer), pss-OS 2 (photostable state) and c-OS 2 (closed-ring isomer) at the same concentration. (c) Thermal decay plot of absorbance versus time of c-OS 2 monitored at 353, 402 and 471 nm at 333 K. (d) Electrostatic potential distribution of closed-ring isomers c-OS 2 and c-OS 4. (e) Absorbance spectra of the photostationary state (PSS) of OS1, OS 2, OS 3 and OS 4 in THF solution. (f) Fluorescence spectra of OS 1, OS 2, OS 3 and OS 4 in THF solution. Excitation for fluorescence is set at 468, 471, 506 and 507 nm, respectively. (g) Fluorescence spectra of OS 2 upon UV light (λ = 313 ± 10 nm), excited at 472 nm, the maximum absorption wavelength in the visible region. (h) Fluorescent on/off contrast ratios of OS 1, OS 2, OS 3 and OS 4 in THF solution upon excitation by ultraviolet and visible light, respectively. (i) Absorption and fluorescence spectral changes of OS 3 in THF (2.0 × 10-5 M) upon irradiation with UV light (313 nm) and subsequent visible light (λ > 470 nm). The solid line showed the absorption spectrum and dashed lines showed the corresponding emission spectra.#

更为有趣的是，带有强给电子取代基的OS‑3和OS‑4展现出独特的单可见光驱动光致异构化能力。研究人员发现，当用488 nm或560 nm可见光照射开环异构体时，原本在该波段无明显吸收的分子竟然发生了环化反应。如图3所示，OS‑4在560 nm光照下达到15.6%的环化转化率，这在以往报道中极为罕见。进一步分析表明，开环异构体在450–600 nm范围内的吸收系数与光子能量呈指数关系，符合Urbach尾态吸收规律，证实了该现象源于振动激发态的热跃迁。这种“带尾吸收”效应使得分子能够利用长波长可见光同时驱动环化与环断裂反应，为单激光调控奠定了基础。

Fig. 3 Visible light-driven photo-responsive behaviour. (a) Absorption spectra changes of the closed form of OS 4 upon irradiation with visible light (λ > 510 nm) in THF (c = 2 × 10-5 M). (b) Absorption spectra of o-OS 3 and o-OS 4 upon irradiation with visible light (λ = 488 ± 10 nm) to photostable state (PSS) in THF (2 × 10-5 M). The solid line showed the absorption spectrum of corresponding closed-ring isomers. (c) Transformation between the open-ring isomer o-OS 4 and the closed-ring isomer c-OS 4. (d) 1H NMR spectra of OS 3 upon irradiation with visible light (λ = 488 ± 10 nm) to PSS in CDCl3 (c = 5 × 10−3 M). (e) The photocyclization reaction yields of OS 4 are estimated by comparing 1H NMR before and after 560-nm and 313-nm light irradiation. The chemical shift of the methyl groups on the thiophene rings in o-OS 4 and c-OS 4 are 1.95 ppm and 2.11 ppm. The conversion ratio from open form to PSS was determined by calculating the peak area ratio of Ha and Ha′ in the 1H NMR spectrum of the PSS solution. (f) Absorption spectra of o-OS 4 upon irradiation with visible light (λ = 488 ± 10 nm and 560 ± 10 nm) and UV light (λ = 313 ± 10 nm), respectively, to PSS state in THF (2 × 10-5 M). (g) The absorption of o-OS 4 varies with photon energy in THF (2 × 10-5 M).#

针对聚集态荧光性能，研究团队系统测定了不同水含量THF/水混合溶剂中的荧光变化。如图4所示，随着水含量增至80%，OS‑4闭合异构体的荧光量子产率从溶液态的1.81%跃升至24.6%，增幅达13.6倍，而开环异构体在此条件下几乎不发光，聚集态荧光对比度进一步提升至124倍。粉末状态下，OS‑4同样展现出可逆的光致变色和荧光开关行为。这种显著的聚集诱导发光效应源于大体积桥联结构有效阻碍了分子间π–π堆积，同时活化了分子内振动受限过程。

Fig. 4 Aggregation-induced emission behaviour under visible light excitation. Fluorescence spectra of (a) c-OS 3 (2 × 10-5 M) and (b) c-OS 4 (2 × 10-5 M) in THF/H2O mixtures with different water volume ratios. The excited wavelength of fluorescent measurement is set at 506 nm (c-OS 3) and 507 nm (c-OS 4). (c) Room light (up) and fluorescent (down) pictures of OS 2 powder under UV (λ = 313 ± 10 nm) and visible light (λ > 470 nm) irradiation, in which the fluorescent pictures were recorded under UV light (λ = 365 ± 20 nm). (d) Relative fluorescence intensity I/I0 plots of open-ring isomers and closed-ring isomers of OS 3 (2 × 10-5 M) excited by 506 nm in THF/H2O mixtures with different water ratios. Here, I is the fluorescence intensity with different water ratios, and I0 is initial fluorescence intensity of c-OS 3 in pure THF. (e) Relative fluorescence intensity I/I0 plots of open-ring isomers and closed-ring isomers of OS 4 (2 × 10-5 M) excited by 507nm in THF/H2O mixtures with different water ratios. (f) Photoluminescence quantum yields of OS 2, OS 3 and OS 4 in solution (THF), aggregated (THF/H2O) states and solid states (powder).#

基于上述优异性能，研究团队将OS分子掺杂到聚苯乙烯‑聚环氧乙烷嵌段共聚物中制备了柱状纳米胶束，并用于超分辨成像验证。传统双激光方案中，OS‑2标记的胶束经405 nm紫外光激活、488 nm激发和再次488 nm退活，获得约47 nm的空间分辨率。而OS‑4的优势在于，仅用单束561 nm激光即可同时完成激活、激发和退活全过程。如图5所示，在561 nm连续照射下，OS‑4标记的胶束发生可逆的荧光开关循环，重建的超分辨图像清晰分辨出柱状胶束的边界轮廓，半高宽为49 nm，较传统宽场成像的382 nm分辨率提升了约8倍。488 nm单激光调控同样获得了46 nm的分辨率。这一结果表明，长波长单激光驱动的AIE光开关不仅完全规避了紫外光损伤，而且成像质量与双激光方案相当。

Fig. 5 Super-resolution imaging applications of polymeric micelles. (a) Illustration of the preparation of photoswitches-doped PSt-b-PEO block copolymers. (b) Mechanism of single visible light modulation of activation, excitation and deactivation processes of OS 3 and OS 4 (c) Super-resolution imaging of cylindrical micelles labelled with OS 2 formed from PSt-b-PEO block copolymers: Conventional fluorescence image (left); Super resolution image, 405-nm light activation, excitation, and 488-nm light deactivation (middle); Conventional fluorescence and super-resolution imaging cross-sectional profiles of PSt-b-PEO block copolymer micelles (right). (d) Super-resolution imaging of cylindrical micelles labelled with OS 4 formed from PSt-b-PEO block copolymers: Conventional fluorescence image (left); Super resolution image, 488-nm single light modulation of activation, excitation and deactivation (middle); Cross-sectional profiles of conventional fluorescence and super resolution imaging (right). (e) Super-resolution imaging of cylindrical micelles labelled with OS 4 formed from PSt-b-PEO block copolymers: Conventional fluorescence image (left); Super resolution image, 561-nm single light modulation of activation, excitation and deactivation (middle); Cross-sectional profiles of conventional fluorescence and super resolution imaging (right).#