Strain Effects on the Work Function of an Organic Semiconductor

Establishing fundamental relationships between strain and work function (WF) in organic semiconductors is important not only for understanding electrical properties of organic thin films, which are subject to both intrinsic and extrinsic strains, but also for developing flexible electronic devices. Here we investigate tensile and compressive strain effects on the WF of rubrene single crystals. Mechanical strain induced by thermal expansion mismatch between the substrate and rubrene is quantified by X-ray diffraction. The corresponding WF change is measured by scanning Kelvin probe microscopy. The WF of rubrene increases (decreases) significantly with in-plane tensile (compressive) strain, which agrees qualitatively with density functional theory calculations. An elastic-to-plastic transition, characterized by a steep rise of the WF, occurs at ∼0.05% tensile strain along the rubrene π-stacking direction. The results provide the first concrete link between mechanical strain and WF of an organic semiconductor and have important implications for understanding the connection between structural and electronic disorder in soft organic electronic materials

Why Is β-Me Elimination Only Observed in d⁰ Early Transition Metal Complexes? An Organometallic Hyperconjugation Effect with Consequences for the Termination Step in Ziegler–Natta Catalysis

Two processes, β-H and β-Me migration, have been observed to compete in the termination of alkene oligomerization (Ziegler–Natta catalysts) in certain d0 early transition metal systems. ECP ab initio calculations have been performed to study these processes. Models of intermediates (X2MRq: X = Cl, Cp; M = Zr, Hf, Ti, q = +1; Zr, Nb, q = 0) have been optimized at the HF level with additional single-point energy calculations at the MP2 level. It is shown that the β-Me elimination may be thermodynamically favored over β-H elimination for strongly electron-deficient metal centers. This preference is attributed to the presence of multiple bonding between a d0 transition metal and the methyl group, which behaves like a weak π donor via its occupied πCH3 orbitals. It is therefore analogous to the well documented hyperconjugation in organic chemistry.</p

Why Is β-Me Elimination Only Observed in d⁰ Early Transition Metal Complexes? An Organometallic Hyperconjugation Effect with Consequences for the Termination Step in Ziegler–Natta Catalysis

Two processes, β-H and β-Me migration, have been observed to compete in the termination of alkene oligomerization (Ziegler–Natta catalysts) in certain d0 early transition metal systems. ECP ab initio calculations have been performed to study these processes. Models of intermediates (X2MRq: X = Cl, Cp; M = Zr, Hf, Ti, q = +1; Zr, Nb, q = 0) have been optimized at the HF level with additional single-point energy calculations at the MP2 level. It is shown that the β-Me elimination may be thermodynamically favored over β-H elimination for strongly electron-deficient metal centers. This preference is attributed to the presence of multiple bonding between a d0 transition metal and the methyl group, which behaves like a weak π donor via its occupied πCH3 orbitals. It is therefore analogous to the well documented hyperconjugation in organic chemistry.</p

Can Fluorenone-Based Compounds Emit in the Blue Region? Impact of the Conjugation Length and the Ground-State Aggregation

Fluorenone-based compounds usually emit light in the yellow-red region. While different origins have been assigned to these colors, only a few studies make a direct correlation between the characteristic emission and the lowest absorption energy band (LEB). Intriguingly, striking similarities can be observed in the position, shape, and intensity of the LEB for such compounds with different molecular sizes. This work is focused on these aspects of absorption and emission spectra, by means of density functional theory (DFT) calculations and experimental characterizations of a series of fluorenone-centered compounds of increasing size. Our results show that while the absorption LEB is intrinsically related to a π–π* transition between orbitals strongly localized on the fluorenone core, its position and intensity are affected by the tendency of these compounds to associate/aggregate in their ground state even in solution. The intermolecular CO···HC (aromatic) hydrogen bonds (H-bonds) redshift the absorption maximum position and reduce the intensity of the intramolecular π–π* transition. Under some circumstances these effects disappear, in close correlation with the disappearance of the characteristic absorption LEB. Bright and intense blue emission is then obtained in THF solution instead of the strongly quenched yellow-orange one, indicating that blue constitutes the intrinsic emission color of fluorenone-based compounds

Fairness in agreement with European values: An interdisciplinary perspective on ai regulation

With increasing digitalization, Artificial Intelligence (AI) is becoming ubiquitous. AI-based systems to identify, optimize, automate, and scale solutions to complex economic and societal problems are being proposed and implemented. This has motivated regulation efforts, including the Proposal of an EU AI Act. This interdisciplinary position paper considers various concerns surrounding fairness and discrimination in AI, and discusses how AI regulations address them, focusing on (but not limited to) the Proposal. We first look at AI and fairness through the lenses of law, (AI) industry, sociotechnology, and (moral) philosophy, and present various perspectives. Then, we map these perspectives along three axes of interests: (i) Standardization vs. Localization, (ii) Utilitarianism vs. Egalitarianism, and (iii) Consequential vs. Deontological ethics which leads us to identify a pattern of common arguments and tensions between these axes. Positioning the discussion within the axes of interest and with a focus on reconciling the key tensions, we identify and propose the roles AI Regulation should take to make the endeavor of the AI Act a success in terms of AI fairness concerns. </p