Photoexcitation dynamics in perylene diimide dimers

We utilize first-principles theory to investigate photo-induced excited-state dynamics of functionalized perylene diimide. This class of materials is highly suitable for solar energy conversion because of the strong optical absorbance, efficient energy transfer, and chemical tunability. We couple time-dependent density functional theory to a recently developed time-resolved non-adiabatic dynamics approach based on a semi-empirical description. By studying the monomer and dimer, we focus on the role stacking plays on the time-scales associated with excited-state non-radiative relaxation from a high excitonic state to the lowest energy exciton. We predict that the time-scale for energy conversion in the dimer is significantly faster than that in the monomer when equivalent excited states are accounted for. Additionally, for the dimer, the decay from the second to the nearly degenerate lowest energy excited-state involves two time-scales: a rapid decay on the order of ∼10 fs followed by a slower decay of ∼100 fs. Analysis of the spatial localization of the electronic transition density during the internal conversion process points out the existence of localized states on individual monomers, indicating that the strength of thermal fluctuations exceeds electronic couplings between the states such that the exciton hops between localized states throughout the simulation.Fil: Mukazhanova, Aliya. Boston University; Estados UnidosFil: Malone, Walter. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Negrín Yuvero, Lázaro Hassiel. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Fernández Alberti, Sebastián. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tretiak, Sergei. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Sharifzadeh, Sahar. Boston University; Estados Unido

Understanding excited states and energy transfer in highly ordered organic molecular assemblies

π-stacked organic materials are tunable light absorbers with many potential applications in optoelectronics such as light emitting diodes, solar cells, and photocatalysts. Their optical properties are highly dependent on the nature and energy of electron-hole pairs or excitons formed upon light absorption, which are in turn determined by the intra- and inter-molecular electronic and vibrational excitations. In this dissertation, first principles methods such as density functional theory (DFT), time-dependent DFT (TDDFT), and a recently developed time-resolved non-adiabatic dynamics approach are used to understand excitons and their interactions with atomic vibrations. Perylene diimide (PDI) molecules are studied as a model system to gain physical insight about these phenomena. This class of materials is highly suitable for solar energy conversion because of the strong optical absorbance, efficient energy transfer, and chemical tunability. TDDFT, including vibronic effects, was applied to macromolecular DNA-based surrogates composed of one to three stacked PDI molecules, in order to understand the influence of electronic coupling to vibrational modes on the exciton. This approach is validated by comparison to experimental measurements and it was determined that intra- and inter-molecular interactions result in distinct vibrational, electronic, and optical properties. Additionally, exciton dynamics within these macromolecules is studied, simulating the internal energy decay from a high to lower energy excitonic state due to coupling of the excitation with atomic vibrations. It is shown that stacking leads to enhanced energy decay because of decreased energy spacing between states. Additionally, a new approach is presented to identify the vibrational modes that assist energy transfer, revealing that interactions between stacked molecules modulate the normal modes that couple to the exciton. Lastly, by studying the dynamics of the transition density, it is demonstrated that stacking impacts the localization of the exciton, a key feature of interest for solar energy conversion. For the dimer, the exciton quickly localizes and oscillates between two monomers, while the trimer can host long-time delocalization of the exciton. In summary, by applying first-principles theory, the coupling of inter-/intra-molecular electronic and vibrational excitations and their effects on energy transfer is identified. These findings provide fundamental understanding of the atomic-scale process associated with energy conversion, and provide insight towards rational design of new optoelectronic organic assemblies.2023-08-26T00:00:00

Prevalence of refractive errors and risk factors for myopia among schoolchildren of Almaty, Kazakhstan: A cross-sectional study

Very little is known about the prevalence of refractive errors among children in Kazakhstan. The aim of this study was to investigate the prevalence of refractive errors and risk factors of myopia among schoolchildren in Almaty, Kazakhstan. Methods In the cross-sectional study of 2293 secondary school students (age 6–16), we examined cycloplegic autorefraction and offered a questionnaire in three age groups: 1st grade (N = 769), 5th grade (N = 768) and 9th grade (N = 756). The questionnaire covered main risk factors such as parental myopia, screen time, time outdoors, sports activities, near work, gender, grade, and school shift. Adjusted logistic regression analysis was applied to test the association of risk factors with myopia. Results The mean spherical equivalent (SER) was -0.54 ± 1.51 diopters (D). The overall prevalence of refractive errors was 31.6% (95% confidence interval (CI) 29.7; 33.5); myopia 28.3% (95% CI 26.5; 30.1); hyperopia 3.4% (95% CI 2.7–4.1) and astigmatism 2.8% (95% CI 2.1; 3.5). In the multivariate adjusted regression analysis, higher class level (5th grade (odds ratio (OR) 1.78; 95% CI 1.26; 2.52) and 9th grade (OR 3.34; 95% CI 2.31; 4.82)) were associated with myopia, whereas outdoors activity more than 2 hours a day (OR 0.64; 95% CI 0.46; 0.89) and sports (OR 0.70; 95% CI 0.52; 0.93) were associated with a lower incidence of myopia

Vibronic Photoexcitation Dynamics of Perylene Diimide: Computational Insights

Perylene diimide (PDI) represents a prototype material for organic optoelectronic devices because of its strong optical absorbance, chemical stability, efficient energy transfer, and optical and chemical tunability. Herein, we analyze in detail the vibronic relaxation of its photoexcitation using nonadiabatic excited-state molecular dynamics simulations. We find that after the absorption of a photon, which excites the electron to the second excited state, S2, induced vibronic dynamics features persistent modulations in the spatial localization of electronic and vibrational excitations. These energy exchanges are dictated by strong vibronic couplings that overcome structural disorders and thermal fluctuations. Specifically, the electronic wavefunction periodically swaps between localizations on the right and left sides of the molecule. Within 1 ps of such dynamics, a nonradiative transition to the lowest electronic state, S1, takes place, resulting in a complete delocalization of the wavefunction. The observed vibronic dynamics emerges following the electronic energy deposition in the direction that excites a combination of two dominant vibrational normal modes. This behavior is maintained even with a chemical substitution that breaks the symmetry of the molecule. We believe that our findings elucidate the nature of the complex dynamics of the optically excited states and, therefore, contribute to the development of tunable functionalities of PDIs and their derivatives.Fil: Negrín Yuvero, Lázaro Hassiel. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mukazhanova, Aliya. Boston University; Estados UnidosFil: Freixas Lemus, Victor Manuel. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tretiak, Sergei. No especifíca;Fil: Sharifzadeh, Sahar. Boston University; Estados UnidosFil: Fernández Alberti, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentin

Octopus-inspired deception and signaling systems from an exceptionally-stable acene variant.

Multifunctional platforms that can dynamically modulate their color and appearance have attracted attention for applications as varied as displays, signaling, camouflage, anti-counterfeiting, sensing, biomedical imaging, energy conservation, and robotics. Within this context, the development of camouflage systems with tunable spectroscopic and fluorescent properties that span the ultraviolet, visible, and near-infrared spectral regions has remained exceedingly challenging because of frequently competing materials and device design requirements. Herein, we draw inspiration from the unique blue rings of the Hapalochlaena lunulata octopus for the development of deception and signaling systems that resolve these critical challenges. As the active material, our actuator-type systems incorporate a readily-prepared and easily-processable nonacene-like molecule with an ambient-atmosphere stability that exceeds the state-of-the-art for comparable acenes by orders of magnitude. Devices from this active material feature a powerful and unique combination of advantages, including straightforward benchtop fabrication, competitive baseline performance metrics, robustness during cycling with the capacity for autonomous self-repair, and multiple dynamic multispectral operating modes. When considered together, the described exciting discoveries point to new scientific and technological opportunities in the areas of functional organic materials, reconfigurable soft actuators, and adaptive photonic systems

Octopus-inspired deception and signaling systems from an exceptionally-stable acene variant

Abstract Multifunctional platforms that can dynamically modulate their color and appearance have attracted attention for applications as varied as displays, signaling, camouflage, anti-counterfeiting, sensing, biomedical imaging, energy conservation, and robotics. Within this context, the development of camouflage systems with tunable spectroscopic and fluorescent properties that span the ultraviolet, visible, and near-infrared spectral regions has remained exceedingly challenging because of frequently competing materials and device design requirements. Herein, we draw inspiration from the unique blue rings of the Hapalochlaena lunulata octopus for the development of deception and signaling systems that resolve these critical challenges. As the active material, our actuator-type systems incorporate a readily-prepared and easily-processable nonacene-like molecule with an ambient-atmosphere stability that exceeds the state-of-the-art for comparable acenes by orders of magnitude. Devices from this active material feature a powerful and unique combination of advantages, including straightforward benchtop fabrication, competitive baseline performance metrics, robustness during cycling with the capacity for autonomous self-repair, and multiple dynamic multispectral operating modes. When considered together, the described exciting discoveries point to new scientific and technological opportunities in the areas of functional organic materials, reconfigurable soft actuators, and adaptive photonic systems