Effects of Intermolecular Interactions on the Singlet–Triplet Energy Difference: A Theoretical Study of the Formation of Excimers in Acene Molecules

The effects of intermolecular interactions in the excited state of acene molecules on the singlet–triplet energy difference (Δ<i>E</i>_ST) were investigated by carrying out <i>ab initio</i> calculations at the SOS-CIS­(D₀)/aug-cc-pVDZ level. Benzene, naphthalene, and anthracene molecules were employed, and their Δ<i>E</i>_ST values were compared with those of their respective cofacial excimers. Our theoretical results demonstrate that, upon the formation of excimer, the Δ<i>E</i>_ST values decrease significantly. By carrying out an excitation energy decomposition, we found that Δ<i>E</i>_ST, albeit also modulated by the changes in orbital energy difference and Coulomb energy, is dominated by the difference in exchange energy between the singlet and triplet states, with the exchange energy decreasing as the intermolecular interactions become stronger. The natural transition orbital analysis suggests that the decrease in the exchange energy may be caused by the different nature of the hole and electron wave functions of the excimers (antibonding vs bonding), which gives rise to their spatial separation. Furthermore, it was found that the geometry relaxation effects depend on the spin state, thus leading to a further reduction of Δ<i>E</i>_ST

Flowchart of the process of obtaining a 3D reconstructed volume of elastic-type objects using the virtual focusing method.

<p>Flowchart of the process of obtaining a 3D reconstructed volume of elastic-type objects using the virtual focusing method.</p

Reconstruction of an elastic-type object showing regular contraction that is continuous in time.

<p>(a) Process of deformation of an elastic-type object during scanning. Objects with different sizes are captured at different projection angles (0°, 90°, 180°). (b) Sinogram in the process of deformation. The amplitude of the sinogram gradually decreases with respect to the projection angle. (c) Sinogram modified by moving the projected shadow of the object to rescale the pixel values. (d) Sinogram after rescaling the pixel values to the contracted original-size sample (left) and to the final-size sample (right). (e) Convert non-ideal sinogram pattern into ideal sinogram pattern from each sinogram in (d) with a translation error using the virtual focusing method. (f) Ideally focused reconstructions from the sinograms in (e) for the original-size sample(left) and final-size sample(right).</p

Local-Excitation versus Charge-Transfer Characters in the Triplet State: Theoretical Insight into the Singlet–Triplet Energy Differences of Carbazolyl-Phthalonitrile-Based Thermally Activated Delayed Fluorescence Materials

The singlet–triplet energy differences, Δ<i>E</i>_ST, of a series of carbazolyl-phthalonitrile (CzPN) derivatives were calculated at the levels of density functional theory (DFT) and time-dependent (TD) DFT using the gap-tuned, range-separated ωB97X functional. The studied CzPN derivatives include 4-(9<i>H</i>-carbazol-9-yl)­phthalonitrile (CzPN), 4,5-di­(9<i>H</i>-carbazol-9-yl)­phthalonitrile (2CzPN), 3,4,5-tris­(9<i>H</i>-carbazol-9-yl)­phthalonitrile (3CzPN), and 3,4,5,6-tetra­(9<i>H</i>-carbazol-9-yl)­phthalonitrile (4CzPN). As additional Cz substituents are introduced, both the HOMO–LUMO energy gap, Δ<i>E</i>_H–L, and Δ<i>E</i>_ST continuously decrease. Both natural transition orbital analysis and a quantitative assessment of the local-excitation (LE) and charge-transfer (CT) contributions to the excited states consistently demonstrate that the S₁ states of all of the CzPN derivatives have a predominantly CT nature. In contrast, in the T₁ state, the LE feature is dominant, but the CT character increases with the number of Cz groups. The decomposition of excitation energy reveals that, in addition to the spatial separation of HOMO and LUMO, a significant CT nature in the T₁ state is essential for a further reduction in Δ<i>E</i>_ST. Moreover, the relative proportions of LE and CT characters in the T₁ states of the CzPN derivatives can be modulated with Δ<i>E</i>_H–L

Determination of the motion modes using four fixed points.

<p>(a) Original image sample with four fixed points (high-density area). <i>d</i>₁ is the distance between the left and right fixed points, and <i>d</i>₂ is the distance between the top and bottom fixed points. (b) Distance between fixed points on the original image in the CCD. <i>θ</i> represents a projection angle. (c) Distance between fixed points on the regularly contracted image in the CCD. (d) Sinogram in the process of regular contraction. A high density in the sinogram represents the circular trajectory of the fixed points. (e) Distance between fixed points on the elliptically contracted image in the CCD. (f) Sinogram in the process of elliptic contraction. A high density in the sinogram represents the circular trajectory of the fixed points.</p

Change in the common layer for an elastic-type specimen and a schematic of two elastic specimens showing regular and elliptical contraction.

<p>(a) 3D image samples in space (left panel) and a front view. The gray part indicates the common layer. The first object (purple) is used to create five other objects by changing the size or height. The sizes of the first three samples are 10 × 10 × 10, 20 × 10 × 10, and 20 × 20 × 10, from the left, respectively. The next three samples are those whose heights from the first three samples have been doubled (10 × 10 × 20, 20 × 10 × 20, and 20 × 20 × 20, respectively). When the heights of the first three samples are doubled, the height of the common layer also doubles. (b) Schematic of a specimen that regularly contracts: 3D image (left), front view (middle), and side view (right). The common layer should be calculated for the thickness of the axial level considering the deformation rate of the object. (c) Schematic of a specimen that elliptically contracts. The figures are the 3D image (left), front view (middle), and side view with a middle axial level (right). The common layer should be calculated to be the same as (b) that with the elliptical deformation rate.</p

Changes in the CCD and the projection angle for the common area of the sample when X-rays penetrate samples of different sizes.

<p>(a) Original image specimen with a projection angle. When the X-ray for projection angle <i>θ</i> passes the crossed area of the image sample, the size of the area projected onto the CCD is Δ<i>l</i>₁. (b) Regularly contracted image specimen. The X-ray projection angle for the common area does not change by <i>θ</i>; however, the size of the area projected onto the CCD decreases to Δ<i>l</i>₂. (c) Elliptically contracted image specimen. The X-ray projection angle for the common area changes to <i>θ</i>′, and the size of the area projected onto the CCD is changed to Δ<i>l</i>₃.</p

Difference in the relative errors.

<p>(a) 746 × 746 image sample, where the gray part is the region of interest. (b) Blue curve is the relative error that is calculated after the CA of the resized projection image is transformed into the CA of the original projection image. The red curve is the relative error that is calculated when the CA of the original-size projection image moves one voxel and the CA of the original-size projection image does not move.</p

Electronic Structure of Carbazole-Based Phosphine Oxides as Ambipolar Host Materials for Deep Blue Electrophosphorescence: A Density Functional Theory Study

We report the results of Density Functional Theory calculations on a series of carbazole-based phosphine oxides that experimental data have shown to be promising ambipolar host molecules for deep blue electrophosphorescence. The hosts under investigation contain either 1, 2, or 3 carbazole subunits attached to the phenyl rings of a triphenylphosphoryl group, with the carbazoles acting as hole transporters/acceptors and the triphenylphosphoryl groups as electron transporters/acceptors. The results underline that, in addition to the strong inductive effect of the phosphoryl groups, the LUMO of these hosts is further stabilized by the molecular orbital interactions among the phenyl rings of the triphenylphosphoryl group, which is modulated by the electron-withdrawing inductive effects of the carbazole subunits. The lowest triplet state of the hosts correspond to localized transitions within the carbazole units, which leads to a high triplet energy on the order of 3 eV. We describe the important buffer role of the phenyl rings in preventing the phosphoryl moiety from negatively affecting the hole-accepting characteristics and high triplet energies of the carbazole units

Quality of domiciliary services from a user's perspective

Petra Slaná ABSTRACT The thesis "Quality of domiciliary services from a user's perspective" deals with issues of quality of care services. Its aim was to find out what users expect from a quality service. Based on qualitative research and knowledge gained from practice was also to create a methodology for user satisfaction domiciliary services. The thesis consists of two parts, theoretical and empirical. The theoretical part contains the definition of old age, approaching the issue of aging, self-sufficiency and human needs in old age. It provides demographic and statistic data about the aging population. It focuses on social services in general, their definition, types and forms. It outlines the form of social services for seniors in the Czech Republic and in selected countries of European Union. It describes systems of quality used in the commercial sphere and in the service area. The theoretical part concludes with an overview of the factors which determine user satisfaction. The aim of the empirical part was to identify areas that may be an important quality of service criteria. Thanks to these users can evaluate the quality of services. To achieve this aim, was chosen qualitative research method. The empirical part of this thesis is therefore devoted to qualitative methodology of the research,..