Lucia Maini

Phosphorescence quantum yield enhanced by intermolecular hydrogen bonds in Cu4I4 clusters in the solid state.

Organo-copper(i) halide complexes with a Cu4I4 cubane core and cyclic amines as ligands have been synthesized and their crystal structures have been defined. Their solid state photophysical properties have been measured and correlated with the crystal structure and packing. A unique and remarkably high luminescence quantum yield (76%) has been measured for one of the complexes having the cubane clusters arranged in a columnar structure and held together by N-HI hydrogen bonds. This high luminescence quantum yield is correlated with a slow radiationless deactivation rate of the excited state and suggests a rather strong enhancement of the cubane core rigidity bestowed by the hydrogen bond pattern. Some preliminary thin film deposition experiments show that these compounds could be considered to be good candidates for applications in electroluminescent devices because of their bright luminescence, low cost and relatively easy synthesis processes.

Making crystals with a purpose; a journey in crystal engineering at the University of Bologna

The bottom-up preparation of mixed crystals, co-crystals and photoreactive materials starting from molecular building blocks across the borders of organic, organometallic and metal–organic chemistry is described.

Synergic effect of unsaturated inner bridges and polymorphism for tuning the optoelectronic properties of 2,3-thieno(bis)imide based materials

2,3-Thieno(bis)imide (N) ended oligomers are emerging as valuable molecular materials for applications in organic electronics. Here, we report the synthesis and characterization of three new 2,3-thieno(bis)imide ended oligothiophenes (T) bearing unsaturated ethylene (E), azomethine (I) and ethinyl (A) inner bridges (NTE, NTI and NTA, respectively). The effect of the unsaturated bridge on the π-conjugation extent, molecular conformation and overall aromaticity is related to the functional optoelectronic and morphological properties and compared to the properties of the linear analogue (NTT) with a bithiophene inner moiety. Optical spectroscopy and cyclovoltammetry analysis show a strong red shift of the absorption and an increased energy band gap on going from NTI and NTE to NTA. The HOMO level decreases in the order NTE > NTI > NTA. Moreover, while the LUMO of NTE and NTA have almost the same energy, NTI has a LUMO energy about 0.1 eV lower, likely due to the electron withdrawing effect of the azomethine moiety. Morphological investigation of solution cast thin deposits shows that the unsaturated bridges promote the formation of concomitant polymorphs with the simultaneous presence of microcrystals with different morphology and fluorescence properties. Moreover, irreversible conversion of one polymorph to the other was achieved by thermal treatments for NTA and NTE and by exploiting this feature, we realized a time temperature integrator (TTI) device based on NTE material. This device allowed to monitor temperature evolutions in the range between RT and 200 °C by means of a red to yellow fluorescence switch that was detectable by optical microscopy.

White luminescence achieved by a multiple thermochromic emission in a hybrid organic–inorganic compound based on 3-picolylamine and copper(I) iodide

Three copper(i) complexes have been obtained by the reaction of CuI with 3-picolylamine in acetonitrile solution and characterized by X-ray powder diffraction, both from synchrotron and laboratory radiation. Photophysical investigations in the solid state revealed highly efficient thermally-activated delayed fluorescence (TADF) with photoluminescence quantum yields (PLQYs) up to 18%. Notably, the complex [Cu2I2(3pica)]∞ displays a strong luminescence thermochromism due to the presence of both 1,3(X + M)LCT excited states and a lower-lying cluster-centered (3CC) one, leading to multiple emission at room temperature; as a result, a white luminescence is achieved with a PLQY of 4.5%.

Crystal form selectivity by humidity control: the case of the ionic co-crystals of nicotinamide and CaCl2

Post-synthesis (de)hydration techniques were used here to explore further hydrated forms of ionic co-crystals (ICCs) of nicotinamide with CaCl2. Humidity is shown to be a crucial factor for ICCs, which cannot be ignored for a complete polymorph screening of this class of compounds. The exposure of nicotinamide·CaCl2·H2O obtained by kneading reaction to a controlled relative humidity of 75% led to the formation of a new hydrated phase: nicotinamide·CaCl2·4H2O. When nicotinamide·CaCl2·H2O was exposed to a relative humidity between 32% and 54%, nicotinamide2·CaCl2·2H2O was obtained. The anhydrous form was achieved as the result of overnight dehydration of nicotinamide·CaCl2·H2O at 150 °C. The tetrahydrate form cannot be obtained as a first product for kinetic (or thermodynamic) reasons. Control of the relative humidity has proven to be an efficient way to selectively isolate and stabilize powders of pure hydrous ICC phases, which is fundamental for industrial applications. Crystalline structures of nicotinamide·CaCl2·4H2O and anhydrous nicotinamide·CaCl2 were determined by powder diffraction.

Structural Investigation of Poly(ethylene furanoate) Polymorphs

α and β crystalline phases of poly(ethylene furanoate) (PEF) were determined using X-ray powder diffraction by structure resolution in direct space and Rietveld refinement. Moreover, the α’ structure of a PEF sample was refined from data previously reported for PEF fiber. Triclinic α-PEF a = 5.729 Å, b = 7.89 Å, c = 9.62 Å, α = 98.1°, β = 65.1°, γ = 101.3°; monoclinic α’-PEF a = 5.912 Å, b = 6.91 Å, c = 19.73 Å, α = 90°, β = 90°, γ = 104.41°; and monoclinic β-PEF a = 5.953 Å, b = 6.60 Å, c = 10.52 Å, α = 90°, β = 107.0°, γ = 90° were determined as the best fitting of X-ray diffraction (XRD) powder patterns. Final atomic coordinates are reported for all polymorphs. In all cases PEF chains adopted an almost planar configuration.

Anhydrous ionic co-crystals of cyanuric acid with LiCl and NaCl

Anhydrous ionic co-crystals (ICCs) of cyanuric acid (CA) with sodium and lithium chlorides have been prepared by solid state methods and structurally characterized from X-ray powder diffraction data (XRPD). Complete encapsulation of the Li+Cl− ion pair by the organic molecules is observed in CA·LiCl, while the solid-state solvation of piles of Na+ cations in CA·NaCl results in the markedly increased dissolution rate (ca. 5 times) and solubility (ca. 20 times) in water with respect to pure CA.

From isomorphous to "anisomorphous" ionic co-crystals of barbituric acid upon dehydration and return

The isomorphous hydrated ionic co-crystals (ICCs) of barbituric acid (BA) of the formula BA·MBr·2H2O (M = Na, K, Rb) can be easily dehydrated to the corresponding anhydrous ICCs BA·MBr (M = Na, K, Rb). The three anhydrous crystals possess different structures that revert to the isomorphous crystals upon hydration. Only BA·RbBr is stable in air, making it possible to determine its crystal structure from single-crystal X-ray diffraction. BA·NaBr and BA·KBr rapidly absorb water from air and convert to the hydrated form. The crystal structures of BA·NaBr and BA·KBr have been determined by X-ray powder diffraction in sealed capillaries. Solid-state NMR spectroscopy was fundamental in determining the number of independent molecules in the asymmetric unit for the structural determination of the ICC BA·NaBr. The dehydration process was characterized by variable temperature X-ray powder diffraction, DSC and TGA.

Crystal forms of the hydrogen oxalate salt of o-desmethylvenlafaxine.

To prepare new crystalline forms of the antidepressant o‐desmethylvenlafaxine salt as potential new commercial forms and evaluate their physicochemical properties, in particular the dissolution rate.

Crystal Structure and Physicochemical Characterization of Ambazone Monohydrate, Anhydrous, and Acetate Salt Solvate

The crystal structures of the monohydrate and anhydrous forms of ambazone were determined by single-crystal X-ray diffraction (SC-XRD). Ambazone monohydrate is characterized by an infinite three-dimensional network involving the water molecules, whereas anhydrous ambazone forms a two-dimensional network via hydrogen bonds. The reversible transformation between the monohydrate and anhydrous forms of ambazone was evidenced by thermal analysis, temperature-dependent X-ray powder diffraction and accelerated stability at elevated temperature, and relative humidity (RH). Additionally, a novel ambazone acetate salt solvate form was obtained and its nature was elucidated by SC-XRD. Powder dissolution measurements revealed a substantial solubility and dissolution rate improvement of acetate salt solvated form in water and physiological media compared with ambazone forms. Also, the acetate salt solvate displayed good thermal and solution stability but it transformed to the monohydrate on storage at elevated temperature and RH. Our study shows that despite the requirement for controlled storage conditions, the acetate salt solvated form could be an alternative to ambazone when solubility and bioavailability improvement is critical for the clinical efficacy of the drug product.