Four Slip-Stacked Arrangements, Three Types of Photophysics: Crystal Structure and Solid-State Fluorescence of 3,6-Diaryl Substituted Furo[3,4-c]furanone Polymorphs and Regioisomers.

Six symmetrical 3,6-diaryl (aryl=phenyl, 2-, 3- and 4-tolyl, 2,4- and 3,5-xylyl) substituted furo[3,4-c]furanones (DFF) were synthesized. The computational analysis, based on density functional theory, found eight possible centrosymmetrical slipped π-stack arrangements, formed according to electron repulsion minimization principle, as for previously reported for π-isoelectronic diketopyrrolopyrroles (DPP). One of these slipped stack arrangements was found to form infinite columns in the crystals of a new polymorph of parent phenyl derivative (with centre-to-centre distance CC=6.975 Å), other three types of stacks were found for 3-tolyl (CC=6.153 Å), 4-tolyl (CC=3.849 Å) and 2,4-xylyl (CC=4.856 Å) derivatives by single crystal X-ray diffractometry. All six derivatives show intense solution fluorescence in blue/green region, with a maximum driven entirely by a number and position of methyl substituents on phenyl rings. On the other hand, the solid-state fluorescence from yellow over orange to red is observed only for four derivatives and its presence/absence, spectral position and vibronic structure is driven exclusively by the slips in π-stacks (with interplanar distance always less than 3.5 Å) of almost planar DFF molecules, resulting in J-type emission, H-type excimer-like emission and H-type quenching.

Salt-kneading: alternative sizing of active pharmaceutical ingredients?

The most of currently produced active pharmaceutical ingredients (APIs) are poorly soluble in the human body. One of the options how to increase their dissolution rate is reducing their particle size. If very small particles of API are desired, traditional milling methods often cause smeared, agglomerated or non-flowing particles due to the forces applied. We tried to compare some of milling methods with the salt-kneading method, which is not typically used in the pharmaceutical industry. Salt-kneading process is driven by several variable parameters (e.g. the amount, hardness and particle size of the salt-kneading material), which influence the degree of size reduction of API particles which are chafed by a surplus of salt-kneading material. A model poorly-soluble API was separately processed with oscillation mill, vibratory mill and kneader; and the morphology, size distribution and solid form of prepared particles were analyzed. Our basic variation of salt-kneading parameters showed the potential of the salt-kneading method, which appears a very effective method of API controlled reduction. The final size can be modified according to the amount and properties of the salt-kneading material. The availability of such a method equips pharmaceutical scientists with a size-reduction method that provides very small, rounded and free-flowing particles of the poorly soluble API and reduces non-preferred needle shape.

Comparative studies of diphenyl-diketo-pyrrolopyrrole derivatives for electroluminescence applications.

Four different derivatives of diphenyl-diketo-pyrrolopyrrole (DPP) with alkyl side groups were synthesized to increase their solubility. Quantum chemical calculations revealed that the substitution influenced molecular geometry and subsequently modified absorption and photoluminescence spectra. The theoretical results were confirmed by experimental characterization. With increasing phenyl torsion the vibrational structure was less pronounced and larger Stokes shift was observed. Simultaneously, the molar absorption coefficient decreased as the deformation increased. On the other hand, the measured fluorescence quantum yields were modified only slightly. This indicates the possibility to prepare soluble derivatives without loss of quantum yields and to use these materials for construction of efficient and stable electroluminescent devices. Furthermore, the electroluminescence of the thin layer devices based on the soluble low molecular DPPs were characterized and discussed.