One of the key catalytic reactions for life on earth, the oxidation of water to molecular oxygen, occurs in the oxygen‐evolving complex of the photosystem II (PSII) mediated by a manganese‐containing cluster. Considerable efforts in this research area embrace the development of efficient artificial manganese‐based catalysts for the oxygen evolution reaction (OER). Using artificial OER catalysts for selective oxygenation of organic substrates to produce value‐added chemicals is a worthwhile objective. However, unsatisfying catalytic performance and poor stability have been a fundamental bottleneck in the field of artificial PSII analogs. Herein, for the first time, a manganese‐based anode material is developed and paired up for combining electrocatalytic water oxidation and selective oxygenations of organics delivering the highest efficiency reported to date. This can be achieved by employing helical manganese borophosphates, representing a new class of materials. The uniquely high catalytic activity and durability (over 5 months) of the latter precursors in alkaline media are attributed to its unexpected surface transformation into an amorphous MnOx phase with a birnessite‐like short‐range order and surface‐stabilized MnIII sites under extended electrical bias, as unequivocally demonstrated by a combination of in situ Raman and quasi in situ X‐ray absorption spectroscopy as well as ex situ methods.
Organic pi-conjugated polymers are deemed to be soft materials with strong electron-phonon coupling, which results in the formation of polarons, i.e., charge carriers dressed by self-localized distortion of the nuclei. Universal signatures for polarons are optical resonances below the band gap and intense vibrational modes (IVMs), both found in the infrared (IR) spectral region. Here, we study p-doped conjugated homo-and copolymers by combining first-principles modelling and optical spectroscopy from the far-IR to the visible. Polaronic IVMs are found to feature absorption intensities comparable to purely electronic transitions and, most remarkably, show only loose resemblance to the Raman or IR-active modes of the neutral polymer. The IVM frequency is dramatically scaled down (up to 50%) compared to the backbone carbon-stretching modes in the pristine polymers. The very large intensity of IVMs is associated with displacement of the excess positive charge along the backbone driven by specific vibrational modes. We propose a quantitative picture for the identification of these polaron shifting modes that solely based on structural information, directly correlates with their IR intensity. This finding finally discloses the elusive microscopic mechanism behind the huge IR intensity of IVMs in doped polymeric semiconductors.
organic semiconductors (OSCs) that can be easily processed with low-cost, largethroughput fabrication techniques. While high carrier mobilities are generally desirable, optoelectronic devices, such as organic light-emitting diodes [1] and organic photovoltaics, [2] specifically profit from ambipolar transport, i.e., balanced electron and hole transport. However, the majority of OSCs are predominantly unipolar, and demonstrate higher hole mobilities than electron mobilities. [3] Therefore, device fabrication typically requires the deposition of multiple unipolar OSCs to achieve the desired electrical properties, thereby complicating the fabrication protocols.Soluble small-molecule semiconductors that form crystalline films have the potential to combine the advantages of high chemical purity and superior (opto)electronic properties with good processability. However, crystalline organic films formed from soluble small molecules often display poor structural and thermal integrity, as well as lower carrier mobilities compared to nonsoluble small-molecule derivatives. In other words, processability generally comes at the expense of both reduced thermal and mechanical stability, as well as electrical transport.In this study, we synthesized soluble small-molecule dyes that form crystalline films at room temperature, but A key challenge in the field of organic electronics is predicting how chemical structure at the molecular scale determines nature and dynamics of excited states, as well as the macroscopic optoelectronic properties in thin film. Here, the donor-acceptor dyes 4,7-bis[5-[4-(3-ethylheptyl)-2,3-difluorophenyl]-2-thienyl]-2,1,3-benzothiadiazole (2,3-FFPTB) and 4,7-bis[5-[4-(3-ethylheptyl)-2,6-difluorophenyl]-2-thienyl]-2,1,3-benzothiadiazole (2,6-FFPTB) are synthesized, which only differ in the position of one fluorine substitution. It is observed that this variation in chemical structure does not influence the energetic position of the molecular frontier orbitals or the ultrafast dynamics on the FFPTB backbone.However, it does result in differences at the macroscale, specifically regarding structural and electrical properties of the FFPTB films. Both FFPTB molecules form crystalline films at room temperature, whereas 2,3-FFPTB has two ordered smectic phases at elevated temperatures, and 2,6-FFPTB does not display any liquid crystalline phases. It is demonstrated that the altered location of the fluorine substitution allows to control the electrostatic potential along the molecular backbone without impacting molecular energetics or ultrafast dynamics. Such a design strategy succeeds in controlling molecular interactions in liquid crystalline phase, and it is shown that the associated molecular order, or rather disorder, can be exploited to achieve ambipolar transport in FFPTB films.
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