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The porous transport layer (PTL) in polymer electrolyte membrane (PEM) electrolyzers governs the overall efficiency. Its structural, thermal, and electronic properties determine how effortlessly the gases can be produced and can exit the PEM electrolyzer. In this study, we apply a stochastic reconstruction method for titanium felt-based PTLs to generate PTLs with different porosity, fiber radii, and anisotropy parameters. The morphology and topology of these PTLs are numerically characterized, and transport properties, such as gas diffusion coefficients and electrical and thermal conductivity, are computed via pore-scale modeling. Customized graded PTLs are proposed, exhibiting the optimal topology and bulk structure for the removal of gases, the conductance of electrons, and the transport of heat. The results indicate that the surface and transport properties of PTLs can be tailored by certain morphology parameters: PTLs with lower porosity and smaller fiber radii feature a more sufficient interfacial contact and superior electrical and thermal conductivity. Lowering the anisotropy parameters of PTLs results in a slight loss of interfacial contact but a substantial increase in the electrical and thermal conductivity in the through-plane direction. We outline that the design of PTLs should be differentiated depending on the operating conditions of electrolyzers. For nonstarvation conditions, PTLs should feature low porosity and small fiber radii, whereas for starvation conditions, PTLs should feature high porosity, low anisotropy parameters, and small fiber radii. Furthermore, graded PTLs with enhanced structural and transport properties can be developed by customizing the porosity, fiber radius, and fiber orientation.

Cyclopentadienyls are well-known strong donor ligands and have been successfully employed in catalysis as they tolerate a variety of substituents to adjust their steric and electronic properties. Although such highly modifiable ligands are of great interest for luminescence and photocatalytic applications, studies of Cp R -containing photoactive transition-metal complexes are quite rare. In this work, we present a structural, electrochemical, and first elaborated photophysical investigation of a series of copper(I) half-sandwich complexes bearing cyclic alkyl(amino)carbenes (CAACs) as chromophore ligands and compare them with [Cu(Cp)(IDipp)] and [Cu(Cp*)(IDipp)] bearing a traditional N -heterocyclic carbene. Furthermore, we present the first molecular structure derived from single-crystal X-ray diffraction of a copper(I) indenyl complex, which can be described as an η 2 (σ, π)-coordination. The Cu I half-sandwich complexes show blue-green to orange phosphorescence with a photoluminescence quantum yield of up to 59% and radiative rate constants k r of up to 4 × 10 4 s -1 in the solid state, depending on the substitution pattern of the Cp R ligand. Our TD/DFT calculations suggest that the emitting excited states are of 3 MLCT/LLCT character. We determined the excited-state lifetime of the Cu I half-sandwich complexes in solution to be as long as 600 ns, which in combination with the large π-surface of the Cp R ligands allows for Dexter energy transfer for photocatalytic applications. In addition, the chiroptical properties of chiral [Cu(Cp/Cp*)(CAAC Menthone )] were studied and compared to [CuCl(CAAC Menthone )], of which we demonstrate that its circular polarized luminescence is the result of excimer formation and not, as previously reported, attributed to the monomeric C 1 -symmetric structure.

Molecular near-IR (NIR) triplet-state emitters are of importance for the development of new, organic-electronics-based telecommunication technologies as optical fibers operating in the corresponding spectral bands allow for data transfer over much longer distances due to the significantly lower attenuation. However, achieving such low-energy triplet excited states with good radiative rate constants is very challenging, and studies regarding the single-photon emission of organometallics in this energy range are scarce. We have prepared a series of trigonal Cu I CAAC complexes bearing chelating ligands with O, N, S, and Se donor atoms and studied their photophysical properties in this context. The compounds show weak low-energy absorption in solution between 400 and 500 nm due to mixed Cu → CAAC 1 MLCT/LLCT states, resulting in yellow-green to orange appearance, which we have also correlated to the 15 N NMR resonances of the π-accepting carbene ligand. In the solid state, phosphorescence from dominant 3 (Cu → CAAC) CT states is observed at room temperature. The emission of the complexes is bathochromically shifted in comparison to structurally related linearly coordinated copper(I) CAAC complexes due to structural reorganization in the excited state to a T-shape. For [Cu(dbm)(CAAC Me )], the broad phosphorescence with outstanding λ max = 760 nm tailors out to ca. 1100 nm and leads to its proof-of-concept application as a nonclassical single-photon light source, constituting key functional units for the implementation of tap-proof data transfer.

Designing highly efficient purely organic phosphors at room temperature remains a challenge because of fast non-radiative processes and slow intersystem crossing (ISC) rates. The majority of them emit only single component phosphorescence. Herein, we have prepared 3 isomers (o, m, p-bromophenyl)-bis(2,6-dimethylphenyl)boranes. Among the 3 isomers (o-, m- and p-BrTAB) synthesized, the ortho-one is the only one which shows dual phosphorescence, with a short lifetime of 0.8 ms and a long lifetime of 234 ms in the crystalline state at room temperature. Based on theoretical calculations and crystal structure analysis of o-BrTAB, the short lifetime component is ascribed to the T 1 M state of the monomer which emits the higher energy phosphorescence. The long-lived, lower energy phosphorescence emission is attributed to the T 1 A state of an aggregate, with multiple intermolecular interactions existing in crystalline o-BrTAB inhibiting nonradiative decay and stabilizing the triplet states efficiently., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)