全谱吸收之外：解析染料敏化金属有机框架中从光吸收到光催化的激发态迷宫
Beyond Panchromatic Absorption: Deciphering the Excited-State Maze from Light Absorption to Photocatalysis in Dye-Sensitized MOFs
AI总结：
本研究建立多光谱框架解析染料敏化MOFs的激发态，区分有效与非有效吸收红移，揭示互变异构陷阱机制，提出S_Exc描述符，为光敏剂设计提供靶向电荷转移流形的方向。
AI中文摘要：
金属有机框架（MOFs）是极具潜力的光催化剂，可通过连接基官能化拓展其可见光吸收范围；但吸收边红移并不一定能保证效率提升。本研究建立多光谱框架，利用二维光致发光（PL/PLE） mapping 和波长分辨连续波X波段电子顺磁共振（photo-EPR）解析重氮敏化UiO-66中光激发态的光物理归宿。通过关联可见光吸收与photo-EPR和PLE作用光谱，区分出“有效红移”与“非有效发射红移”。高活性UiO-66-茴香醚（活性为TiO₂的97%）中，photo-EPR追踪到新吸收带，证实激发态布居于电荷转移路径，产生持久的自旋分离态；而低活性UiO-66-β-萘酚（活性仅4%）的可见光吸收拓展由PLE追踪，但photo-EPR未检测到，这反映激发态被邻位OH基团形成的刚性分子内氢键捕获，锁定酮-腙互变异构体并破坏偶氮桥共轭。新光学重叠描述符（S_Exc）可定量捕捉该系列的权衡关系。研究表明，光敏剂设计必须抑制刚性互变异构陷阱，靶向特定电荷转移流形（λ≤500 nm），而非仅最大化表观全谱吸收宽度。
英文摘要：
Metal--organic frameworks (MOFs) are promising photocatalysts whose visible-light absorption can be extended through linker functionalization; however, a red-shifted absorption edge does not guarantee enhanced efficiency. Here, we establish a multi-spectroscopic framework to decipher the photophysical fate of photoexcited states in diazo-sensitized UiO-66 using 2D photoluminescence (PL/PLE) mapping and wavelength-resolved continuous-wave X-band photo-EPR. By correlating visible absorption with photo-EPR and PLE action spectra, we distinguish a \textit{productive red shift} from a \textit{non-productive emissive red shift}. In highly active UiO-66-Anisole (97\% activity relative to \ch{TiO2}), photo-EPR tracks the new absorption band, confirming that excitation populates a charge-transfer pathway yielding persistent, spin-separated states. Conversely, poorly active UiO-66-$β$-naphthol (4\%) exhibits an extended visible absorption tracked by PLE but not photo-EPR. This reflects excitation trapping in a localized state caused by an \textit{ortho}-$\mathrm{OH}$ group forming a rigid intramolecular hydrogen bond, which locks the keto-hydrazone tautomer and disrupts the conjugated azo bridge. A new optical overlap descriptor ($S_{\mathrm{Exc}}$) quantitatively captures this trade-off across the series. We demonstrate that photosensitizer design must suppress rigid tautomeric traps and target specific charge-transfer manifolds ($λ\le 500$~nm) rather than merely maximizing apparent panchromatic absorption breadth.
