Role Of Molecular Packing Research Articles

Role of molecular packing in RTP features of positional isomers: The case study of triimidazo-triazine functionalized with ethynyl pyridine moieties

Organic materials characterized by multi-component emissive behavior including RTP features are extremely desirable for various applications. Frequently, long lasting emissions of solids are originated from intermolecular interactions whose role is far from being fully understood. In this context, positional isomers with similar molecular properties but different packing arrangement can be a useful tool to get a deeper comprehension of the mechanisms involved in the solid state emissive behavior. Here, the results obtained on two derivatives of cyclic triimidazole (TT) functionalized with a pyridin-2-yl or 4-yl ethynyl group are presented and interpreted through spectroscopical, structural and computational studies. The two isomers are hardly emissive in solution but become good emitters in blended PMMA films displaying almost overlapping fluorescence and phosphorescence. In solid-state, two additional lower energy phosphorescences are activated through the establishment of either π-π stacking or synergic π-π/hydrogen bond interactions. Stronger aggregated RTP features are observed in the pyridin-2-ylethynyl derivative which displays tighter π-π stacking interactions.

Role of Molecular Packing in Solvent-Mediated Ellagic Acid·Phenazine Co-Crystals Toward Biological Activity Enhancement and Rational Drug Design

Role of Molecular Packing in Solvent-Mediated Ellagic Acid·Phenazine Co-Crystals Toward Biological Activity Enhancement and Rational Drug Design

Thermoelectric properties of organic charge transfer salts from first-principles investigations: role of molecular packing and triiodide anions

Our work indicates that the decoupling relationship and distinctive temperature dependence of thermoelectric parameters can be obtained by regulating molecular arrangements and electronic structures of charge-transfer salts.

The Role of Molecular Packing in Dictating the Miscibility of Some Cholesteryl n-Alkanoates at Interfaces.

Cholesteryl n-alkanoates of saturated fatty acids and their mixtures are widely studied in different physical states and also due to their significance in biology. Here, we address the miscibility of some homologues of cholesteryl n-alkanoates at interfaces, which are known to exhibit different (cholesteryl octanoate, ChC8, and cholesteryl stearate, ChC18) or the same (cholesteryl nonanoate, ChC9, and cholesteryl laurate, ChC12) molecular packing in bulk. Surface manometry and Brewster angle microscopy studies on ChC8 (cholesteryl-cholesteryl interaction, referred to as m-i packing)/ChC9 (cholesteryl-chain interaction, referred to as m-ii packing) and also on ChC18 (chain-chain interactions, referred to as the crystalline bilayer)/ChC9 mixtures reveal phase separation at the air-water (A-W) interface plausibly due to the difference in the molecular packing. In contrast, ChC12/ChC9 (both m-ii packing) mixtures form a homogeneous phase and exhibit a higher collapse pressure (almost twice) than that of ChC9 indicating higher stability. At the air-solid (A-S) interface, the height profiles extracted from the surface topography images using an atomic force microscope yielded thicknesses of 3.6 ± 0.1 and 5.6 ± 0.1 nm for ChC18/ChC9 mixtures (at 0.66 and 0.5 mole fractions (MF)) corresponding to individual assembly, whereas a uniform thickness of 3.5 ± 0.2 nm is obtained for the case of ChC12/ChC9 mixtures (at 0.2, 0.5, and 0.8 MF) corresponding to m-ii packing. Ellipsometry studies reveal that the desorption temperature increases with the mole fraction of ChC9 and attains a maximum at 406.8 ± 4.8 K for 0.4 MF of ChC9, beyond which it decreases. Raman spectroscopy studies are carried out for ChC12/ChC9 mixtures in the homogeneous phase and in the collapsed state. Here, the dependency of peak positions on different physical states was assessed. Our studies offer new insights into the compatibility of molecular packing influencing the phase behavior and may be of relevance to tear film studies and on the formation of crystals in atherosclerosis.

Fabrication of Conjugated Porous Polymer Catalysts for Oxygen Reduction Reactions: A Bottom-Up Approach

The present study demonstrates the fabrication of a conjugated porous polymer (CPP-P2) through a Pd-catalyzed Suzuki–Miyaura poly-condensation reaction. 13C cross-polarization solid-state NMR and Fourier transform infrared (FTIR) spectroscopy were used to characterize CPP-P2. Pristine nitrogen-containing CPP was explored as a catalyst for the oxygen reduction reaction in 0.1 M KOH aqueous alkaline media. In the case of CPP-P2,the polymer oxygen reduction reaction occurs via a four-electron transfer mechanism. An understanding of the oxygen reduction at the molecular level and the role of molecular packing in the three-dimensional structure was proposed based on density functional theory (DFT) modeling.

DNA association-enhanced physical stability of catanionic vesicles composed of ion pair amphiphile with double-chain cationic surfactant

Physical stability control of vesicle/DNA complexes is a key issue for the development of catanionic vesicles composed of ion pair amphiphile (IPA) as DNA carriers. In this work, physical stability characteristics of the complexes of DNA with positively charged catanionic vesicles composed of an IPA and a double-chain cationic surfactant, dihexadecyldimethylammonium bromide (DHDAB), were explored. It was found that in water, the mixed IPA/DHDAB catanionic vesicles became stable when the mole fraction of DHDAB (xDHDAB) was increased up to 0.5. The improved physical stability of the vesicles with a high xDHDAB could be related to the enhanced electrostatic interaction between the vesicles. When the catanionic vesicles interacted with DNA, excellent physical stability was detected for the vesicle/DNA complexes especially with a high xDHDAB. However, this could not be fully explained by the electrostatic interaction effect, and the role of molecular packing within the vesicular bilayers was apparently important. The corresponding Langmuir monolayer study demonstrated that the molecular packing of mixed IPA/DHDAB layers became ordered with DNA association due to inhibited desorption of the positively charged moiety of the IPA. Moreover, the DNA association-induced improvement in the molecular packing of the mixed IPA/DHDAB layers became pronounced with increased xDHDAB. The results imply that one can fabricate catanionic vesicle/DNA complexes with excellent physical stability through the improved molecular packing in the IPA vesicular bilayers with DHDAB addition and DNA association.

Role of Molecular Packing in Determining Solid-State Optical Properties of π-Conjugated Materials.

The optical properties of π-conjugated organic molecules in their solid state are critically important in determining performance efficiencies of optoelectronic devices such as organic light-emitting diodes and organic thin-film transistors. This Perspective discusses some recent systematic explorations aimed toward arriving at an understanding of the role that molecular packing plays in determining these properties.

Enhancing performance of planar molecule-based organic light-emitting diodes through deposition-rate optimization: Role of molecular packing

The authors report a systematic study on the influence of the film deposition rate on the performance of organic light-emitting diodes (OLEDs) based on planar bis(10-hydroxybenzo[h]qinolinato) beryllium. The lower the deposition rate is, the lower the electroluminescence efficiency is. The observation is attributed to easier formation of ordered Bebq 2 aggregates for slower deposition rates, which result in higher electron mobility and lower photoluminescence (PL) efficiency. The faster degradation in both PL efficiency and electron injection accounts for the decreased device lifetime with the decrease in the deposition rate. The role of molecular packing in device performance is discussed.

Cross-dimerization of nitrosobenzenes in solution and in solid state

Cross-linking of nitrosobenzenes to heterodimers (azodioxides) when they are not sterically crowded with large groups in ortho-position was studied by NMR and FT-IR spectroscopy, X-ray crystallography as well as by cryogenic photolysis. It was found for the first time that cross-linked dimers (heterodimers) exist both in solution and in solid state and that they appear in the crystal together with homodimers. The system is used as a model for studying organic solid solution formation. The role of molecular packing in formation of a weak chemical bond is also discussed.

Solid State Optical Properties of 4-Alkoxy-pyridine Butadiene Derivatives: Reversible Thermal Switching of Luminescence

The synthesis and optical properties of a series of alkoxyphenyl-pyridyl butadiene derivatives in solution and in the solid state are described. All the derivatives were practically nonfluorescent in solution but showed good fluorescence in the solid-state. The role of molecular packing in controlling the solid-state fluorescence was investigated by studying the X-ray crystal structure of these molecules. One of the derivatives, 4-((1E,3E)-4-(4-butoxyphenyl)buta-1,3-dienyl)pyridine exhibited polymorphism, with the different polymorphs exhibiting visually distinguishable fluorescence. In the natural state it existed as a polymorph exhibiting blue fluorescence, while it’s cooled melt emitted yellow light. The difference could be attributed to a transformation in the molecular packing of the material from a herringbone to a brickstone arrangement, resulting in a change from monomer to J-type aggregate fluorescence. The polymorph exhibiting yellow fluorescence was fairly stable (>6 months) but could be converted back to the original form by keeping the film at 110 °C for a short period of time (∼8–10 min) before slowly cooling to room temperature. The thermally induced changes in fluorescence behavior were clearly reproducible over several cycles, indicating the utility of this material for thermal imaging applications.

Surface Tension Obtained from Various Smectic-A Liqujd-Crystal Free-Standing Films

Employing a straightforward experimental technique, we have investigated the surface tension of various liquid crystal compounds in the smectic-A and smectic-Ad phases. The results clearly demonstrate the significant role of molecular packing in determining the surface tension.

Role of molecular packing and structural defects in reactions of gases with organic solids: ozonolysis of trans-stilbene and αβ-diethyl-4,4′-dihydroxystilbene

Optical microscopic examination of partially ozonolysed and wet-etched single-crystal faces of trans-stilbene (1a) and αβ-diethyl-4,4′-dihydroxystilbene-(1b) reveal the importance of line defects (dislocations) in governing the rate of the (anisotropic) oxidative attack of the ethylenic double bond in these two solids. In the regions of enhanced reactivity at dislocations emergent on the (100) face of (1b) the rate of ozonolysis is considerably slower than at corresponding regions of the (001) face of (1a), a direct consequence of the protection afforded to the double bond in molecules of the former. As reaction product [benzaldehyde and p-hydroxypropiophenone for (1a and b) respectively] accumulates within each solid reactant, stresses are set up which generate more dislocations on well-defined slip planes (which are identified); these, in turn, function as new centres of preferred attack so that the reaction accelerates as ozonolysis proceeds. Very many new slip systems in crystals of (1a), and relatively few new ones in crystals of (1b), are activated by the accumulation of reaction product. This is explicable in terms of the crystallographic differences between the two solids. It is directly demonstrated that numerous new families of dislocations may be introduced during the course of a gas–solid reaction; and many of the slip systems identified here for (1a) have not hitherto been detected in other aromatic solids (such as naphthalene and anthracene) which also belong to the space group P21/a.