Computational Chemistry of Compounds with Donor-Acceptor Interactions

<p>Compounds with donor-acceptor interactions find important applications in catalysis, C-H activation, phosphorus activation, selective oxidation and cyclization. Moreover, they are potential candidates for use in the synthesis of materials, polymers and light-harvesting systems. The efficient use of a chemical entity is possible when we know its structural and bonding properties. This computational study is intended for the same by studying in detail the structure and bonding properties of donor-acceptor complexes of heavier main-group metals with cyclophane ligands and some heterobimetallic complexes. Additionally, we explored the fluorescence characteristics of benzanthrone dyes. The first part (i.e. main group metal complexes) involves the exploration of structural features and thermal properties through DFT optimization and then calculating the change in enthalpy of formation for all the possibilities under consideration. For this purpose we selected the last three elements from each of Groups 13, 14 and 15 to explore their different coordination modes with two cyclophane ligands; [2.2.2]paracyclophane and deltaphane. We opted for chlorides of each metal to allow them to coordinate from outside the phenyl rings of the cyclophane cavity and from the top of the cavity. To see the coordination of the metals with the inner core of the selected cyclophanes, we put metal cations in the centre of the cavity and optimized. Subsequently, the bonding properties of these inclusion complexes have been analysed in detail on the basis of Morokuma-Ziegler energy decomposition analysis. Secondly, we investigated the structure and bonding properties of some indium-zinc heterobimetallic compounds through geometry optimization, NBO analysis and quantum theory of atoms in molecules (QTAIM) analysis--also known as Bader's analysis. We propose that the heterobimetallic reactant involves donor-acceptor bond that cleaves as a result of the addition of mesityl azide. The newly formed complex has In-N and Zn-N bonds. In the final part benzanthrone dyes containing intramolecular donor-acceptor interactions, (and hence, undergoing intramolecular charge transfer) were subject to the computational investigation of the mechanism of fluorescence taking place in them. Electronic excitations and the structure of first excited state in each case has been discussed thoroughly based on the time-dependent density functional theory. To check for the non-radiative loss of energy, we also performed calculations for the vertical excitations of the triplet states of all the molecules under study. To get a deeper insight into the intramolecular charge transfer, we performed NTO analysis that gives us information based on different colours in regions of charge accumulation and charge depletion.</p>

Computational Chemistry of Compounds with Donor-Acceptor Interactions

<p>Compounds with donor-acceptor interactions find important applications in catalysis, C-H activation, phosphorus activation, selective oxidation and cyclization. Moreover, they are potential candidates for use in the synthesis of materials, polymers and light-harvesting systems. The efficient use of a chemical entity is possible when we know its structural and bonding properties. This computational study is intended for the same by studying in detail the structure and bonding properties of donor-acceptor complexes of heavier main-group metals with cyclophane ligands and some heterobimetallic complexes. Additionally, we explored the fluorescence characteristics of benzanthrone dyes. The first part (i.e. main group metal complexes) involves the exploration of structural features and thermal properties through DFT optimization and then calculating the change in enthalpy of formation for all the possibilities under consideration. For this purpose we selected the last three elements from each of Groups 13, 14 and 15 to explore their different coordination modes with two cyclophane ligands; [2.2.2]paracyclophane and deltaphane. We opted for chlorides of each metal to allow them to coordinate from outside the phenyl rings of the cyclophane cavity and from the top of the cavity. To see the coordination of the metals with the inner core of the selected cyclophanes, we put metal cations in the centre of the cavity and optimized. Subsequently, the bonding properties of these inclusion complexes have been analysed in detail on the basis of Morokuma-Ziegler energy decomposition analysis. Secondly, we investigated the structure and bonding properties of some indium-zinc heterobimetallic compounds through geometry optimization, NBO analysis and quantum theory of atoms in molecules (QTAIM) analysis--also known as Bader's analysis. We propose that the heterobimetallic reactant involves donor-acceptor bond that cleaves as a result of the addition of mesityl azide. The newly formed complex has In-N and Zn-N bonds. In the final part benzanthrone dyes containing intramolecular donor-acceptor interactions, (and hence, undergoing intramolecular charge transfer) were subject to the computational investigation of the mechanism of fluorescence taking place in them. Electronic excitations and the structure of first excited state in each case has been discussed thoroughly based on the time-dependent density functional theory. To check for the non-radiative loss of energy, we also performed calculations for the vertical excitations of the triplet states of all the molecules under study. To get a deeper insight into the intramolecular charge transfer, we performed NTO analysis that gives us information based on different colours in regions of charge accumulation and charge depletion.</p>

Unveiling structure-performance relationships from multi-scales in non-fullerene organic photovoltaics

Unveiling the correlations among molecular structures, morphological characteristics, macroscopic properties and device performances is crucial for developing better photovoltaic materials and achieving higher efficiencies. To achieve this goal, a comprehensive study is performed based on four state-of-the-art non-fullerene acceptors (NFAs), which allows to systematically examine the above-mentioned correlations from different scales. It’s found that extending conjugation of NFA shows positive effects on charge separation promotion and non-radiative loss reduction, while asymmetric terminals can maximize benefits from both terminals. Another molecular optimization is from alkyl chain tuning. The shortened alkyl side chain results in strengthened terminal packing and decreased π-π distance, which contribute high carrier mobility and finally the high charge collection efficiency. With the most-acquired benefits from molecular structure and macroscopic factors, PM6:BTP-S9-based organic photovoltaics (OPVs) exhibit the optimal efficiency of 17.56% (certified: 17.4%) with a high fill factor of 78.44%, representing the best among asymmetric acceptor based OPVs. This work provides insight into the structure-performance relationships, and paves the way toward high-performance OPVs via molecular design.

Simulations of cosmic ray propagation

We review numerical methods for simulations of cosmic ray (CR) propagation on galactic and larger scales. We present the development of algorithms designed for phenomenological and self-consistent models of CR propagation in kinetic description based on numerical solutions of the Fokker–Planck equation. The phenomenological models assume a stationary structure of the galactic interstellar medium and incorporate diffusion of particles in physical and momentum space together with advection, spallation, production of secondaries and various radiation mechanisms. The self-consistent propagation models of CRs include the dynamical coupling of the CR population to the thermal plasma. The CR transport equation is discretized and solved numerically together with the set of MHD equations in various approaches treating the CR population as a separate relativistic fluid within the two-fluid approach or as a spectrally resolved population of particles evolving in physical and momentum space. The relevant processes incorporated in self-consistent models include advection, diffusion and streaming propagation as well as adiabatic compression and several radiative loss mechanisms. We discuss, applications of the numerical models for the interpretation of CR data collected by various instruments. We present example models of astrophysical processes influencing galactic evolution such as galactic winds, the amplification of large-scale magnetic fields and instabilities of the interstellar medium.

Influence of nighttime radiation fog on the development of the daily boundary layer: An large eddy simulation study

&lt;p&gt;Apart from hazards associated with deep fog, its presence significantly alters the properties of the nocturnal boundary layer (NBL).&amp;#160;&lt;br&gt;The NBL is typically characterized by a stable stratification resulting in weak or sometimes intermittent turbulence.&amp;#160;&lt;br&gt;In contrast, the NBL during deep fog is often convective, as for the longwave radiation optical thick fog layer, the net radiative loss takes place at the fog top, destabilizing the atmosphere from above.&lt;br&gt;Therefore, processes as modified longwave cooling, shortwave absorption, turbulent mixing, reduction of the total water content through droplet settling or modified dewfall, is able to induce differences between the stable NBL (SNBL) and foggy NBL.&amp;#160;&lt;br&gt;Albeit after sunrise the SNBL is quickly transformed into a convective boundary layer (CBL), properties of the NBL are transferred into the day and affect the CBL.&amp;#160;&lt;br&gt;Even though fundamental and applied research have significantly improved fog forecasts and contributed to a broader and deeper understanding at the process-level in the last decades, common numerical weather prediction (NWP) models still miss a significant amount of fog events.&lt;br&gt;A number of complex small-scale processes (such as turbulent mixing, land-atmosphere interactions, aerosol and cloud microphysics and radiation) interacting on different scales have to be correctly resolved or parameterized.&lt;br&gt;Likewise, the prerequisite formation conditions must be presented precisely as they are highly sensitive to slight changes in temperature, humidity or soil moisture, entailing that even small biases in the forcing data could lead to an incorrect representation of subtle supersaturations and might result in failing to predict fog.&lt;/p&gt;&lt;p&gt;Thus, we will present in this talk results of idealized large eddy simulations pairs (with and without the possibility to form fog) covering the diurnal cycle based on a typical fog event observed in Cabauw considering radiative conditions between February and April.&amp;#160;&lt;br&gt;As we performed several parameter studies we will demonstrate, that the CBL in cases without fog is warmer and obtain higher inversion heights than in simulations with fog during night.&lt;br&gt;Further, we show that this temperature deviations are mainly driven by an stronger integrated &amp;#160;longwave cooling during night in the foggy cases.&lt;br&gt;Moreover, we identified the liquid water path as a crucial parameter determining the strength of the fog impact on CBL development.&amp;#160;&lt;/p&gt;

Light Intensity Dependence of Current Density–voltage Characteristics of an Organic Solar Cell and Dominance Switching Between Shockley-read-hall and Radiative Recombination Losses

We investigated the variation of current density-voltage (J-V) characteristics of an organic solar cell (OSC) in the dark and at 9 different light intensities ranging from 0.01 to 1 sun of the AM1.5G spectrum. All three conventional parameters, short-circuit currents (Jsc), open-circuit voltage (Voc), and Fill factor (FF), representing OSC performance evolved systematically in response to light intensity increase. Unlike Jsc that showed quasi-linear monotonic increase, Voc and FF showed distinctive non-monotonic variations. To elucidate the origin of such variations, we performed extensive simulation studies including Shockley-Read-Hall (SRH) recombination losses. Simulation results were sensitive to defect densities, and simultaneous agreement to 10 measured J-V curves was possible only with the defect density of 5 * 1012 cm-3 . Based on analyses of simulation results, we were able to separate current losses into SRH- and radiative-recombination components and, moreover, identify that the competition between SRH- and radiative-loss currents were responsible for the aforementioned variations in Jsc, Voc, and FF. In particular, we verified that apparent demarcation in Voc, and FF variations, which seemed to appear at different light intensities, originated from the same mechanism of dominance switching between recombination losses.

An observationally constrained model of strong magnetic reconnection in the solar chromosphere

Context. The evolution of the photospheric magnetic field plays a key role in the energy transport into the chromosphere and the corona. In active regions, newly emerging magnetic flux interacts with the pre-existent magnetic field, which can lead to reconnection events that convert magnetic energy into thermal energy. Aims. We aim to study the heating caused by a strong reconnection event that was triggered by magnetic flux cancelation. Methods. We use imaging and spectropolarimetric data in the Fe I 6301& 6302 Å, Ca II 8542 Å, and Ca II K spectral lines obtained with the CRISP and CHROMIS instruments at the Swedish 1-m Solar Telescope. These data were inverted with the STiC code by performing multi-atom, multi-line, non-local thermodynamic equilibrium inversions. These inversions yielded a three-dimensional model of the reconnection event and surrounding atmosphere, including temperature, velocity, microturbulence, magnetic field, and radiative loss rate. Results. The model atmosphere shows the emergence of magnetic loops with a size of several arcseconds into a pre-existing predominantly unipolar field. Where the reconnection region is expected to be, we see an increase in the chromospheric temperature of roughly 2000 K as well as bidirectional flows of the order of 10 km s−1 emanating from there. We see bright blobs of roughly 0.2 arcsec in diameter in the Ca II K, moving at a plane-of-the-sky velocity of the order of 100 km s−1 and a blueshift of 100 km s−1, which we interpret as ejected plasmoids from the same region. This scenario is consistent with theoretical reconnection models, and therefore provides evidence of a reconnection event taking place. The chromospheric radiative losses at the reconnection site are as high as 160 kW m−2, providing a quantitative constraint on theoretical models that aim to simulate reconnection caused by flux emergence in the chromosphere.