arXiv subjects

Eugenio Otal

Publications and source records attributed to Eugenio Otal.

3 recordsLinked to original sources

arXiv2025

Mechanistic Origin of Charge Separation and Enhanced Photocatalytic Activity in D-$π$-A-Functionalized UiO-66-NH$_2$ MOFs

Donor-$π$-acceptor (D-$π$-A) functionalization of MOF linkers can enhance visible-light photocatalytic activity, yet the mechanisms responsible for these effects remain unclear. Here we combine EPR spectroscopy, transient photoluminescence, and first-principles calculations to examine how diazo-coupled anisole, diphenylamine (DPA), and N,N-dimethylaniline (NNDMA) groups modify the photophysics of UiO-66-NH$_2$. All donor units introduce new occupied states near the valence-band edge, enabling charge separation through dye-to-framework electron transfer. Among them, the anisole-modified material stands out for facilitating efficient intersystem crossing into a triplet charge-transfer configuration that suppresses fast recombination and yields long-lived charge carriers detectable by photo-EPR. Meanwhile, bulkier donors such as DPA and NNDMA - despite their stronger electron-donating character - also tend to introduce defect-associated trap states. These results underscore the interplay between donor-induced electronic-structure changes, triplet pathways, and defect-mediated recombination, offering a mechanistic basis for tuning photocatalytic response in D-$π$-A-modified MOFs.

cond-mat.mtrl-sci↗

arXiv2025

Unveiling Linker-Born Electron Spin Centers in UiO-66-NH2 MOF

Metal-organic frameworks (MOFs), with their high porosity and large internal surface area, provide versatile platforms for integrating spin centers with potential applications in catalysis and quantum sensing. Here, we identify a stable NH radical spin center in UiO-66-NH2, a zirconium-based MOF with aminoterephthalic acid (TPA-NH2) linkers. Using electron paramagnetic resonance spectroscopy and density functional theory calculations, we determine the nature and spin Hamiltonian parameters of this radical. We also demonstrate that the NH spin center exhibits a relatively long coherence time, making it a strong candidate for quantum sensing. Since this spin center is intrinsic to TPA-NH2 linkers, our findings open new directions for leveraging organic radicals in MOFs for quantum technologies beyond the UiO-66-NH2 family.

cond-mat.mtrl-sci↗

arXiv2024

Photoinduced Spin Centers in Photocatalytic Metal-Organic Framework UiO-66

Metal-Organic frameworks (MOFs) are promising candidates for advanced photocatalytically active materials. These porous crystalline compounds have large active surface areas and structural tunability and are thus highly competitive with oxides, the well-established material class for photocatalysis. However, due to their complex organic and coordination chemistry composition, photophysical mechanisms involved in the photocatalytic processes in MOFs are still not well understood. Employing electron paramagnetic resonance (EPR) spectroscopy and time-resolved photoluminescence spectroscopy (trPL), the fundamental processes of electron and hole generation are investigated, as well as capture events that lead to the formation of various radical species in UiO-66, an archetypical MOF photocatalyst. A manifold of photoinduced electron spin centers is detected, which is subsequently analyzed and identified with the help of density-functional theory (DFT) calculations. Under UV illumination, the symmetry, g-tensors and lifetimes of three distinct contributions are revealed: a surface O2-radical, a light-induced electron-hole pair, and a triplet exciton. Notably, the latter was found to emit (delayed) fluorescence. Our findings provide new insights into the photoinduced charge transfer processes, which are the basis of photocatalytic activity in UiO-66. This sets the stage for further studies on photogenerated spin centers in this and similar MOF materials.

cond-mat.mtrl-sci↗