The energy stored in the triplet states of organic molecules, capable of energy transfer via an emissive process (phosphorescence) or a nonemissive process (triplet-triplet transfer), is actively dissipated in the presence of molecular oxygen. The reason is that photoexcited singlet oxygen is highly reactive, so the photoactive molecules in the system are quickly oxidized. Oxidation leads to further loss of efficiency and various undesirable side effects. In this work we have developed a structurally diverse library of hyperbranched unsaturated poly(phosphoester)s that allow efficient scavenging of singlet oxygen, but do not react with molecular oxygen in the ground state, i.e., triplet state. The triplet-triplet annihilation photon upconversion was chosen as a highly oxygen-sensitive process as proof for a long-term protection against singlet oxygen quenching, with comparable efficiencies of the photon upconversion under ambient conditions as in an oxygen-free environment in several unsaturated polyphosphates. The experimental results are further correlated to NMR spectroscopy and theoretical calculations evidencing the importance of the phosphate center. These results open a technological window toward efficient solar cells but also for sustainable solar upconversion devices, harvesting a broad-band sunlight excitation spectrum.

Understanding the structure and chemical reactivity of water adsorbed at metallic surfaces is very important in many processes such as catalysis, corrosion, and electrochemistry. Using density functional theory calculations, we investigate the adsorption and dissociation of water clusters on flat and stepped surfaces of several transition metals: Rh, Ir, Pd, and Pt. We find that water binds preferentially to the step edges than to terrace sites, thus linear clusters or one-dimensional water wires can be isolated by differential desorption. The clusters formed at the step are stabilized by the cooperative effect of chemical bonds with the metal and hydrogen bonding. The enhanced reactivity of the step edges and the cooperative effect of hydrogen bonding improve the chances of partial dissociation of water clusters. We assess the correlations between adsorption and dissociation energies, observing that they are increased on stepped surfaces. We present a detailed interpretation of water dissociation by analyzing changes in the electronic structure of both water and metals. The identification of trends in the energetics of water dissociation at transition metals is expected to aid the design of better materials for catalysis and fuel cells, where the density of steps at surfaces would be a relevant additional parameter

The interaction of aromatic molecules with metal surfaces is of key relevance for the functionality of molecular electronics and organic electronics devices. One way to control and tune the binding properties of molecules to metals is chemical functionalization. The adsorption of halogenated benzene molecules on the (111) surface of platinum is here investigated by density functional theory calculations with non-local van der Waals correlation functional. It is found that these systems exhibit a bistable adsorption energy profile with (meta)stable chemisorption and physisorption states separated by a potential energy barrier. The relative stability of these states can be tuned by functionalizing benzene with a different number or type of halogen atoms. Our results suggest a simple rational molecular design to achieve the desired interfacial binding in organic electronic devices and in composites with interfaces between large aromatic molecules and metals.

The synthesis of atomically thin boron sheets on a silver substrate opened a new area in the field of two-dimensional systems. Similar to hydrogenated and halogenated graphene, the uniform coating of borophene with fluorine atoms can lead to new derivatives of borophene with novel properties. In this respect, we explore the possible structures of fluorinated borophene for varying levels of coverage (BnF) by using first-principles methods. Following the structural optimizations, phonon spectrum analysis and ab initio molecular dynamics simulations are performed to reveal the stability of the obtained structures. Our results indicate that while fully fluorinated borophene (BF) cannot be obtained, stable configurations with lower coverage levels (B4F and B2F) can be attained. Unveiling the stable structures, we explore the mechanical, electronic, and thermal properties of (BnF). Fluorination significantly alters the mechanical properties of the system, and remarkable results, including direction-dependent variation of Young’s modulus and a switch from a negative to positive Poisson’s ratio, are obtained. However, the metallic character is preserved for low coverage levels, and metal to semiconductor transition is obtained for B2F. The heat capacity at a low temperature increases with an increasing F atom amount but converges to the same limiting value at high temperatures. The enhanced stability and unique properties of fluorinated borophene make it a promising material for various high-technology applications in reduced dimensions.