Beyond Panchromatic Absorption: Deciphering the Excited-State Maze from Light Absorption to Photocatalysis in Dye-Sensitized MOFs
Abstract
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}-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 (SExc) 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≤ 500~nm) rather than merely maximizing apparent panchromatic absorption breadth.
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BibTeX
@misc{kim2026beyond,
title = {{Beyond Panchromatic Absorption: Deciphering the Excited-State Maze from Light Absorption to Photocatalysis in Dye-Sensitized MOFs}},
author = {Manuela L. Kim and Mauricio E. Calvo and Katsuya Teshima and Fabio La Mattina and Eugenio H. Otal},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.00931},
eprint = {2609.00931},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.00931},
}
RIS
TY - UNPB
TI - Beyond Panchromatic Absorption: Deciphering the Excited-State Maze from Light Absorption to Photocatalysis in Dye-Sensitized MOFs
AU - Manuela L. Kim
AU - Mauricio E. Calvo
AU - Katsuya Teshima
AU - Fabio La Mattina
AU - Eugenio H. Otal
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.00931
UR - https://arxiv.org/abs/2609.00931
AB - 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}-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_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≤ 500~nm) rather than merely maximizing apparent panchromatic absorption breadth.
ER -