Martina Dell’angela

Direct spectroscopic identification of the earliest stages of interfacial water activation remains a major challenge in photocatalysis, as the first reaction intermediates are short-lived and rapidly evolve into more stable products. Here, we investigate water activation on an electronically excited two-dimensional covalent triazine framework (CTF) grown on Au(111) using localized water dosing and synchrotron X-ray photoelectron spectroscopy (XPS). Room-temperature measurements reveal persistent chemical species consistent with products of the reaction at the water/CTF interface, whereas low-temperature experiments under an ice overlayer reveal a spectroscopic signature assigned to protonation of triazine nitrogen. This transient feature, likely stabilized by the ice environment, may represent the earliest experimentally accessible chemical consequence of the excited-state water−CTF interaction. Its spectroscopic fingerprint is consistent with the initial proton-transfer step proposed in excited-state proton-coupled electron-transfer (ES-PCET) descriptions of water activation. These results provide direct spectroscopic access to transient interfacial species involved in the initial phase of photocatalytic water activation and establish experimental constraints for mechanistic descriptions based on PCET.

Halogenated diradicaloids display long-lived charge-separated states in solution but short-lived singlets in films, where packing restricts twisting dynamics.

We present that halogen‐substituted and air‐stable Thiele‐type diradicaloids with folded ( 1 ) and planar ( 2 , 3 ) structures can be obtained by switching the positions of fluorine and chlorine substituents. The strongly distorted p ‐quinodimethane 1 demonstrates emission in the UV–visible/near‐infrared (UV–vis/NIR) range with a photoluminescence quantum yield (PLQY) of 100%, an exceedingly large Stokes shift of up to 2.0 eV, an excited state lifetime of 81 ns, and pronounced solvatochromic emission (from 1.81 eV in n ‐pentane to approximately 2.0 eV in dichloromethane). Dual emission in pentane, transient absorption spectroscopy, quantum chemical calculations, as well as the comparison with compounds 2 and 3 reveal that the exceptional photophysical properties of closed‐shell 1 are thanks to interconversion with its planar conformer 1 ^flat . The key here is that the conformer 1 ^flat , which is generated upon photoexcitation, excels with a pronounced singlet diradical character ( y ₀ = 0.78) and a dark doubly excited (DE) S1 state. Our findings delineate how to leverage conformational equilibria to design bright luminescent materials based on hidden and thus air‐stable organic diradicals.

We present that halogen‐substituted and air‐stable Thiele‐type diradicaloids with folded ( 1 ) and planar ( 2 , 3 ) structures can be obtained by switching the positions of fluorine and chlorine substituents. The strongly distorted p ‐quinodimethane 1 demonstrates emission in the UV–visible/near‐infrared (UV–vis/NIR) range with a photoluminescence quantum yield (PLQY) of 100%, an exceedingly large Stokes shift of up to 2.0 eV, an excited state lifetime of 81 ns, and pronounced solvatochromic emission (from 1.81 eV in n ‐pentane to approximately 2.0 eV in dichloromethane). Dual emission in pentane, transient absorption spectroscopy, quantum chemical calculations, as well as the comparison with compounds 2 and 3 reveal that the exceptional photophysical properties of closed‐shell 1 are thanks to interconversion with its planar conformer 1 ^flat . The key here is that the conformer 1 ^flat , which is generated upon photoexcitation, excels with a pronounced singlet diradical character ( y ₀ = 0.78) and a dark doubly excited (DE) S1 state. Our findings delineate how to leverage conformational equilibria to design bright luminescent materials based on hidden and thus air‐stable organic diradicals.

MXenes, the two‐dimensional class of nanomaterials consisting of transition metal carbides, nitrides, or carbonitrides, have been spotlighted in the last decade due to their peculiar properties, allowing them to be applicable in different fields, ranging from energy storage to sensors. In particular, the Ti ₃ C ₂ T _x MXene phase has attracted attention for electronic and optoelectronic applications. In such fields, it is important to characterize the stability of this phase. Testing the stability of the aged sample may provide new hints for the engineering of this phase, ensuring its long‐term performance. X‐ray photoelectron spectroscopy, near‐edge X‐ray absorption fine structure measurements with a synchrotron source, complementary studies with a conventional X‐ray source, and electrical conductivity measurements were employed to characterize the electronic and structural properties of a Ti ₃ C ₂ T _x thin film deposited on a quartz substrate immediately after preparation and again one year later, following storage in a nitrogen‐filled environment. Despite only minor surface oxidation after one year, the conductivity of the aged sample decreased by nearly one order of magnitude compared to the as‐prepared sample, highlighting the need for appropriate precautions if this MXene phase is to be implemented in electronic or optoelectronic devices.

The interfacial energy level alignment in the copper phthalocyanine/SiO₂/p-Si(100) heterojunction has been studied in dark conditions and under illumination. The element-sensitivity of the time-resolved X-ray photoemission provides a real-time picture of the photoexcited carrier dynamics at the interface and within the film, enabling one to distinguish between substrate and molecular contributions. We observe a molecule-to-substrate charge transfer under photoexcitation, which is directly related to the transient modification of the band bending in the substrate due to the surface photovoltage effect. Our results show that charge generation in the heterojunction is driven by the molecular layer in contact with the substrate. The different molecular orientation at the interface creates a new channel for charge injection in the substrate under photoexcitation.

New 2D black phosphorus (bP)–phthalocyanine (Pc) nanohybrids have been synthesized by liquid phase exfoliation of black phosphorus crystals in the presence of two organic dyes: phthalocyanine (Pc) and manganese phthalocyanine (MnPc). The key role of the metal cation in the interfacial interaction between the organic dye and bP nanosheets was demonstrated by X‐ray absorption spectroscopy and associated with an electron transfer between the metal cation Mn²⁺ and bP nanosheets, which resembles a coordinative chemical bond. On the other hand, the interaction between bP nanosheets and pure phthalocyanine is governed by van der Waals forces. The fluorescence of both hybrids is significantly reduced indicating effective separation of the photoinduced charge, implying the formation of a heterojunction between the organic molecules and the bP nanosheets. These findings provide important insights into the interfacial interactions in bP‐Pc nanohybrids that are relevant for application in 2D organic/inorganic devices.

We present a protocol for the on‐surface synthesis of polyboroxine molecules derived from boroxine molecules precursors. This process is promoted by oxygen species present on the Au(111) surface: oxygen atoms facilitate the detachment of naphthalene units of trinaphthyl‐boroxine molecules and bridge two unsaturated boroxine centers to form a boroxine‐O‐boroxine chemical motif. X‐ray spectroscopic characterization shows that, as the synthesis process proceeds, it progressively tunes the electronic properties of the interface, thus providing a promising route to control the electron level alignment.