No abstract

The study of a [1]Benzothieno [3,2-b][1]benzothiophene (BTBT) derivative decorated with hexyl chains functionalized with hydroxyl end groups is reported. A rapid and inexpensive functionalization of the BTBT in position 2 and 7 has been developed. This compound is able to self-organize into a lamellar structure through σ-π stacking and van der Waals interactions but also through hydrogen bonding interactions. The hydrogen-bonded network controls the interlamellar region in terms of organization and stability. Liquid-crystal phase and structural changes observed by DSC have been characterized using an original approach combining FTIR and powder XRD measurements as a function of temperature. Thermally evaporated diol based OFETs exhibited good mobilities up to 0.17 cm².V-1.s-1 measured under inert atmosphere but also in ambient air. The diol derivative is considered as a very promising platform for the design of new functionalized BTBT.

Determination of kryptoracemic compound frequency in the Cambridge Structural Database using CCDC Python API script.

Temperature-resolved second harmonic generation (TR-SHG) and SHG microscopy were used to study under normal pressure the solid–solid transition mechanism occurring between the two monotropically related polymorphic forms (metastable Pna21 and stable P21/n) of 3-hydroxybenzoic acid (MHBA). The activation energy E a (as a measure of the barrier energy) of the irreversible transition was determined via isothermal TR-SHG (137–144 kJ·mol–1). It fits well with that determined from differential scanning calorimetry (139 kJ·mol–1). Regarding the two crystal structures, optical microscopy observations, and kinetics parameters from TR-SHG, a destructive/reconstructive mechanism is proposed for the solid–solid transition. The present study clearly demonstrates that TR-SHG is a relevant and accurate technique for monitoring solid–solid phase transitions.

Phase transitions of 1-fluoro-adamantane have been thoroughly investigated by temperatureresolved second harmonic generation (TR-SHG) and X-ray powder diffraction (XRPD). A new polymorph-an intermediate centrosymmetric phase (MT)-between the known orientationally disordered high temperature phase (HT, F ̅ , Z=4) and low temperature phase (LT, P ̅ , Z=2) was unveiled by TR-SHG. The crystal structure of MT was resolved by XRPD in the P mc (Z=2) space group and it is related to the LT phase in a group-subgroup relation. No evidence of any solid-solid transition between these two phases by differential scanning calorimetry (DSC) or cold-stage microscope could be obtained. Therefore, combing TR-SHG, XRPD, DSC and cold-stage microscope results, a second-order transition mechanism is proposed for MT LT transition. h (β) f w by fitting TR-SHG data to a critical w w. Th b β (0.26) h from XRPD data (0.25).

The application of powder second harmonic generation (P-SHG), temperatureresolved SHG (TR-SHG), and SHG microscopy (SHGM) in the characterization of bulk crystalline samples is illustrated. P-SHG applied to powder samples can be an extremely sensitive approach to detect the absence of an inversion center in crystalline structures, TR-SHG serves to monitor temperature-induced phase transitions, and SHGM is used in the detection of non-centrosymmetric zones inside a heterogeneous material. These methods are of great relevance, e.g., in the pharmaceutical industry where crystalline active pharmaceutical ingredients are often made of a single enantiomer and are therefore non-centrosymmetric. Herein, several examples are provided to describe how a given SHG signal should be interpreted. A general procedure to carry out a P-SHG experiment is illustrated in detail.

The design of molecule-based systems combining magnetic, chiroptical and second-order optical nonlinear properties is still very rare. We report an unusually unsymmetric diiron(III) complex 1, in which three bulky chiral carboranylpyridinealkoxide ligands (oCBhmp(-)) bridge both metal ions and the complex shows the above-mentioned properties. The introduction of o-carborane into the 2-(hydroxymethyl)pyridine (hmpH) architecture significantly alters the coordination of the simple or aryl-substituted 2-hmpH. The unusual architecture observed in 1 seems to be triggered by the poor nucleophilicity of our alkoxide ligand (oCBhmp(-)). A very rare case of spontaneous resolution takes place on precipitation or exposure to solvent vapor for the bulk compound, as confirmed by a combination of single-crystal and powder X-ray diffraction, second-harmonic generation, and circular dichroism. The corresponding enantiopure complexes (+)1 and (-)1 have also been synthesized and fully characterized. This research provides a new building block with unique geometry and electronics to construct coordination complexes with multifunctional properties.

This work illustrates the use of powder second harmonic generation (powder SHG), temperature-resolved second harmonic generation (TR-SHG), and second harmonic generation microscopy (SHGM) in monophasic and multiphasic sample studies. The commercial powder of 3,5-dinitrobenzoic acid was found to exhibit a significant second harmonic generation signal, whereas only two centrosymmetric polymorphic forms have been reported for this compound. Second harmonic generation techniques were used in combination with chromatography, differential scanning calorimetry, and powder X-ray diffraction to show that the SHG activity of 3,5-dinitrobenzoic acid powder originates from a chemical impurity (3-nitrobenzoic acid) present in the commercial powder under the form of a new metastable noncentrosymmetric polymorph. The metastable equilibria between 3,5-dinitrobenzoic acid and 3-nitrobenzoic acid were studied, and SHG analyses performed on crystallized binary mixtures showed significant enhancements of the SHG signal compared to that of the pure noncentrosymmetric phase. This is due to the formation of a suitable eutectic microstructure that enables quasi phase matching (QPM). In particular, powders from near-eutectic compositions exhibit SHG signals up to 20 times higher than that of the powder containing pure 3-nitrobenzoic acid noncentrosymmetric phase. This observation could provide the basis for a new route to achieve new, efficient materials for second-order frequency conversion.