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Four crystalline polymorphs of the proinsecticide chlorfenapyr [4-bromo-2-(4-chlorophenyl)-1-ethoxymethyl-5-trifluoromethyl-1H-pyrrole-3-carbonitrile] have been identified and characterized by polarized light optical microscopy, differential scanning calorimetry, Raman spectroscopy, X-ray diffraction, and electron diffraction. Three of the four structures were considered polytypic. Chlorfenapyr polymorphs show similar lethality against fruit flies (Drosophila melanogaster) and mosquitoes (Anopheles quadrimaculatus) with the least stable polymorph showing slightly higher lethality. Similar activities may be expected to be consistent with structural similarities. Knockdown kinetics, however, depend on an internal metabolic activating step, which further complicates polymorph-dependent bioavailability.

Nicotine, a widely consumed, yet considered toxic, active pharmaceutical ingredient for recreational use, is known to rapidly deteriorate into unwanted and potentially harmful side products. Crystallization with salt formers transforms the unstable oil into solids with tunable properties. However, previously reported salts and co-crystals are not necessarily safe for human consumption, with several containing heavily halogenated coformers. When combined with malic acid, a generally recognized as safe (GRAS) compound, the four resulting crystalline solids exhibited melting points as high as 122 °C and spanned a range of ∼30 °C. The nicotine-based materials also possessed improved degradation properties. A detailed analysis of the crystal packing and thermodynamic properties provides context for the observed properties.

Singlet fission (kSF) and excimer formation (kEXC) rate constants along with other photophysical properties of thin solid layers of 1,3-diphenylisobenzofuran and 11 of its fluorinated derivatives have been determined. The molecular properties of these compounds are similar, but their crystal packing varies widely. Most of them undergo singlet fission whereas excitation in others is trapped in excimers. The trend in rate constants kSFagrees qualitatively with results of calculations by a simplified version of the frontier orbital model for a molecular pair. The main shortcoming of the model is discussed.

Supramolecular engineering bridges molecular assembly with macromolecular charge-transfer salts, promising the design to construct supramolecular architectures that integrate cooperative properties difficult or impossible to find in conventional lattices. Here, we report the crystal engineering design and kinetic growth of one-dimensional supramolecular wires composed of bis(ethylenedithio)tetrathiafulvalene (ET+) cation and polymeric Cu[N(CN)2]2–anion. A bulk ferromagnetic order is discovered for filling up the gap where strong ferromagnetism is missing in such ET molecule-based charge-transfer salts. Metallicity is induced by electric current from the semiconducting wire, which is attributed to strain effect by tuning its close molecular contact. This structural feature is evidenced through the combination of various mechanistic spectroscopic studies. Electric dipole is established from the close molecular contacts and is suggestive to stabilize ferromagnetic spin interaction through anions bridging spin sites. The breakthrough shown here provides a pathway to explore low-dimensional supramolecular materials exhibiting strong electron correlation, metallicity, and ferromagnetism.

C26H24N2O8, monoclinic, P21/c(no. 14), a= 6.9170(9) Å, b= 26.012(3) Å, c= 12.7449(17) Å, β= 91.896(4)°, V= 2291.9(5) Å3, Z= 4, Rgt(F) = 0.0471, wRref(F2) = 0.1320, T = 90 K.

The behavior of excitons and excess electrons in the confined space of a molecular polyoxotitanate cluster Ti17(μ4-O)4(μ3-O)16(μ2-O)4(OPri)20(in short Ti17) was studied using femtosecond pump-probe transient absorption, pulse radiolysis and fluorescence spectroscopy. Due to pronounced quantum size effects the electronic spectra of the exciton, Ti17*, and the excess electron carrying radical anion Ti17•-, are blue-shifted in comparison with bulk TiO2and have maxima at 1.91 and 1.24 eV, respectively. The 0.7 eV difference in the position of the maxima Ti17*and Ti17•-indicates the presence of strong Coulomb interaction between the conduction band electron and the valence band hole in the ~1 nm diameter cluster. Ground state Raman spectra and the vibronic structures of the fluorescence spectrum point to the importance of the interfacial ligand modes in the stabilization and localization of the fully relaxed exciton. Four pentacoordinate Ti sites near the surface of the cluster appear to play a special role in this regard. Solvent polarity has only a minor influence on the spectral behavior of Ti17*. Exciton recombination in Ti17is faster than in anatase nanoparticles or mesoporous films. The kinetics exhibits three components, ranging from less than 1ps to 100 ps, which are tentatively assigned to the geminate recombination within the core of the cluster and to the decay of the surface stabilized charge transfer exciton. A persistent long-lived component with τ > 300 ps may indicate the involvement of intraband dark states, i.e. triplet excitons 3Ti17*.

Diarylethenes (DAEs) are an exciting class of stimulus-responsive organic molecules that exhibit electrocyclization reactions upon exposure to light, heat, or other stimuli. The rational design of DAE-based crystalline materials is, however, complicated by the presence of DAE atropisomers, only one of which is photoactive. Data mining of the CSD produced 1349 unique molecular DAE structures that were subsequently analyzed according to selected chemical and geometric attributes. Additional analyses were performed on 1078 dithienylethene (DTE) structures─the largest subgroup within the ensemble. The crystal structure landscape, based upon D–Dparameterization and analysis, revealed a vast array of molecular geometries, many of which may not correspond to energetic minima. The analyses link various chemical and geometric parameters to isomers observed in the lattice and their reactivity; however, potential biases intrinsic to this ensemble of structures complicate the determination of causal relationships. We believe that this retrospective comprehensive analysis of DAE structures represents an important step for understanding more broadly the crystal landscape of this class of materials.

C8H8O4·C10H8N2, monoclinic, P21/c(no. 14), a= 13.427(4) Å, b= 10.069(3) Å, c= 12.751(4) Å, β= 116.124(7)°, V= 1547.7(8) Å3, Z= 4, Rgt(F) = 0.0426, wRref(F2) = 0.1152, T = 90 K.

Fast hole hopping in Ti17cat4, a 1 nm diameter molecular polyoxotitanate cluster bearing four catechol ligands (Ti17(μ4-O)4(μ3-O)16(μ2-O)4(cat)4(OPri)16), was investigated by ultrafast spectroscopy and quantum dynamics simulations. The catechol moieties coupled to the TiO2core of the cluster give rise to a charge-transfer band, the excitation of which promotes an electron from the highest occupied molecular orbital of the ligand to the inorganic core, resulting in the formation of {cat+•,Ti3+}, a vibrationally hot polaronic exciton. Dynamic depolarization measurements indicate that within less than 100 fs the Franck–Condon polaronic state formed at the interface evolves into a fully charge-separated state and the injected electron delocalizes over the quasi conduction band of the cluster. The positive charge (hole) resulting from the injection does not remain static either. The initial hole hopping between the catechol sites occurs with the rate of ∼5 × 1011s–1or more and competes with the intramolecular vibrational relaxation. Upon thermalization, the hopping slows and continues at a rate of ∼5 × 1010s–1. The experimentally observed rate of hole hopping agrees well with the results of quantum dynamics modeling of the wavepacket propagation.

Mixed crystals of potassium hydrogen phthalate containing 3,6-diaminoacridine were photoexcited with visible light and the resulting triplet excited states were analyzed by time resolved EPR spectroscopy. Spectra from discrete growth sectors were compared with powders and polycrystalline glasses prepared at various pHs. The data yield the predominant protonation state and orientation of the triplets in each of a pair of growth sectors bounding the positive and negative ends of the polar crystal.

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Terahertz time domain spectroscopy (THz TDS) is used to measure the melting kinetics of fructose molecular crystals. Combining single-crystal anisotropy measurements with density functional calculations, we assign the phonon frequencies and interrogate how specific phonons behave with melting. While nearly all the low-frequency phonons continuously red-shift with heating and melting, the lowest-energy phonon polarized along the c-axis blue-shifts at the melting temperature, suggesting an initial structural change immediately before melting. We find that the kinetics follow a 3D growth model with large activation energies, consistent with previous differential scanning calorimetry (DSC) measurements. The large activation energies indicate that multiple H-bonds must break collectively for the transition. The results suggest the generality of the kinetics for molecular crystals and that THz TDS with picosecond resolution could be used to measure ultrafast kinetics.

The single crystals of a closed form spirooxazine spiroazahomoadamantane-isoquinolinoxazine were found for the first time to undergo photocoloration processes consistent with photochromism in the single crystalline phase.