Prehliadanie podľa Autor "Otyepka, Michal"

Teraz sa zobrazuje 1 - 3 z 3
  • Obrázok miniatúry
    Položka
    Computational design of donor-acceptor stacked polycyclic aromatic hydrocarbons as photocatalytic sites in carbon dots
    (The Royal Society of Chemistry : Cambridge, 2025) Hrivnák, Tomáš; Pykal, Martin; Rogach, Andrey L.; Otyepka, Michal; Medveď, Miroslav
    Carbon dots (CDs) are complex carbon-based nanomaterials with exceptional photoluminescence characteristics and great promise for sustainable metal-free photocatalysis. However, their structural heterogeneity poses a major challenge for the rational design and prediction of photocatalytic performance. To overcome this limitation, we propose a bottom-up strategy centered on CD-inspired systems with well-defined molecular architecture. Specifically, we computationally screened 5700 stacked polycyclic aromatic hydrocarbon aggregates, as representatives of CD aromatic domains, to identify donor–acceptor pairs capable of efficient charge separation under photoexcitation. Using a few carefully chosen molecular descriptors and a computationally efficient protocol, we identified best candidate systems for oxidative and reductive quenching pathways. Subsequent time-dependent density functional theory analysis confirmed that these systems exhibit key photocatalytic features: a charge-transfer character in the lowest excited state, well-separated bright local excitations, favorable redox potentials, and propensity for extended aggregation with core-surface charge separation. Our approach not only offers a practical design route for CD-like photocatalysts but also provides the fundamental understanding needed to engineer tunable, efficient, and sustainable donor–acceptor photocatalytic systems.
  • Obrázok miniatúry
    Položka
    Solvent controlled generation of spin active polarons in two-dimensional material under UV light irradiation
    (The American Chemical Society : Washington, 2024) Zoppellaro, Giorgio; Medveď, Miroslav; Hrubý, Vítězslav; Zbořil, Radek; Otyepka, Michal; Lazar, Petr
    Polarons belong to a class of extensively studied quasiparticles that have found applications spanning diverse fields, including charge transport, colossal magnetoresistance, thermoelectricity, (multi)ferroism, optoelectronics, and photovoltaics. It is notable, though, that their interaction with the local environment has been overlooked so far. We report an unexpected phenomenon of the solvent-induced generation of polaronic spin active states in a two-dimensional (2D) material fluorographene under UV light. Furthermore, we present compelling evidence of the solvent-specific nature of this phenomenon. The generation of spin-active states is robust in acetone, moderate in benzene, and absent in cyclohexane. Continuous wave X-band electron paramagnetic resonance (EPR) spectroscopy experiments revealed a massive increase in the EPR signal for fluorographene dispersed in acetone under UV-light irradiation, while the system did not show any significant signal under dark conditions and without the solvent. The patterns appeared due to the generation of transient magnetic photoexcited states of polaronic character, which encompassed the net 1/2 spin moment detectable by EPR. Advanced ab initio calculations disclosed that polarons are plausibly formed at radical sites in fluorographene which interact strongly with acetone molecules in their vicinity. Additionally, we present a comprehensive scenario for multiplication of polaronic spin active species, highlighting the pivotal role of the photoinduced charge transfer from the solvent to the electrophilic radical centers in fluorographene. We believe that the solvent-tunable polaron formation with the use of UV light and an easily accessible 2D nanomaterial opens up a wide range of future applications, ranging from molecular sensing to magneto-optical devices.
  • Obrázok miniatúry
    Položka
    Thermodynamics and kinetics of early stages of carbon dot formation: a case of citric acid and ethylenediamine reaction
    (The Royal Society of Chemistry : Cambridge, 2025) Pykal, Martin; Nociarová, Jela; Řeha, David; Filo, Juraj; Šebela, Marek; Zajíček, Petr; Paloncýová, Markéta; Olla, Chiara; Mocci, Francesca; Cappai, Antonio; Carbonaro, Carlo Maria; Baďura, Zdeněk; Zdražil, Lukáš; Zbořil, Radek; Rogach, Andrey L.; Medveď, Miroslav; Otyepka, Michal
    Owing to their extraordinary photophysical properties, carbon dots (CDs) have found applications across various fields, including bioimaging, sensing, and environmental research. Despite huge application potential, the fabrication of CDs still lacks the desired control at the molecular level, and precise structural regulation towards property-tailored CDs remains elusive. The mechanistic details of nucleation, growth, and carbonization processes leading to CDs are still unknown, with key thermodynamic and kinetic parameters yet to be revealed. Herein, we performed quantum chemical calculations of explicitly micro-hydrated reaction systems to thoroughly explore the mechanism of a prototypical reaction of citric acid and ethylenediamine. The theoretical results showed activation barriers and thermodynamics along the reaction pathway, thus helping identify key heterocyclic intermediates and cyclization products. The cyclization and condensation reactions were further simulated via a reactive molecular dynamics protocol, suggesting potential growth scenarios and generating plausible structures for further exploration of the polymerization and carbonization processes. The theoretical calculations were cross-validated with NMR and MALDI-TOF measurements. The data obtained provide a comprehensive deterministic insight into the initial stages of CD formation, revealing new reaction intermediates and pathways, and rationally predicting the formation of specific structural arrangements of premature CDs. The presented deterministic approach represents an important step towards rational bottom-up design of these unique fluorescence systems.