Design, synthesis and characterization of new luminescent crystalline materials

The research project could be divided in two main topics: (i) the structural and thermal characterization and the polymorph screening of a specific class of semiconducting organic materials: the 2,3-thienoimide (TI) based oligothiophenes; (ii) the synthesis and characterization of new luminescent coordination polymers based on d10 metal halides. The crystal structure determination was carried out both by Single Crystal X-ray diffraction and Powder X-ray diffraction. The 2,3-thienoimide (TI) based oligothiophenes present different crystalline forms that can be obtained by changing the solvent of recrystallization or combining deposition and annealing processes, so part of the work was also dedicated to the study of polymorphism and the analysis of the solid state transition between the different crystal phases. These molecules are characterized by a strong luminescence which dramatically changes depending on the polymorph, this behaviour makes the molecule interesting for potential application in OFET, OLET or TTI. The coordination polymers were obtained by solvothermal reaction, synthesis in solution and by direct grinding of the reagents. The mechanochemistry permits to perform the reaction directly in solid state, overcoming the intrinsic low solubility of Cu(I) and Ag(I) halides, and can yield crystal forms that are not obtainable in solution. However, in several cases the 1-D chain is due to the formation of infinite chain of CuI or AgX which make these compounds closer to the hybrid material than to coordination polymers

AgX-based hybrid coordination polymers: mechanochemical synthesis, structure and luminescence property characterization

Hybrid coordination polymers are interesting for their ability to converge the properties of both inorganic and organic systems in one single compound and recently attention has been focused on silver based hybrid coordination polymers due to their luminescence properties. We searched the CSD to establish the propensity of AgXL (X = Cl-, Br- and I-) with L as an organic ligand to form hybrid coordination polymers. About 800 AgXL structures are deposited in the CSD, with huge structural variability: indeed, it is possible to recognize some structural preferences based on the halide nature. The formation of an inorganic polymeric unit is favoured by iodide but it is also possible with the other halides. This research continues with the synthesis of AgX (X = I-, Br-) based coordination polymers with 2-, 3- and 4-picolylamine (n-pica) as ligands. By mechanochemical synthesis five new hybrid coordination polymers and one coordination polymer have been obtained and their structures determined. While [(AgI)(n-pica)](n) are not luminescent, [(AgBr)(n-pica)](n) emit and their profile depends on the crystallinity of the sample

Structural insights into the vapochromic behavior of Pt- and Pd-based compounds

Anionic complexes having vapochromic behavior are investigated: [K(H2O)][M(ppy)(CN)2], [K(H2O)][M(bzq)(CN)2], and [Li(H2O)n][Pt(bzq)(CN)2], where ppy = 2-phenylpyridinate, bzq = 7,8-benzoquinolate, and M = Pt(II) or Pd(II). These hydrated potassium/lithium salts exhibit a change in color upon being heated to 380 K, and they transform back into the original color upon absorption of water molecules from the environment. The challenging characterization of their structure in the vapochromic transition has been carried out by combining several experimental techniques, despite the availability of partially ordered and/or impure crystalline material. Room-temperature single-crystal and powder X-ray diffraction investigation revealed that [K(H2O)][Pt(ppy)(CN)2] crystallizes in the Pbca space group and is isostructural to [K(H2O)][Pd(ppy)(CN)2]. Variable-temperature powder X-ray diffraction allowed the color transition to be related to changes in the diffraction pattern and the decrease in sample crystallinity. Water loss, monitored by thermogravimetric analysis, occurs in two stages, well separated for potassium Pt compounds and strongly overlapped for potassium Pd compounds. The local structure of potassium compounds was monitored by in situ pair distribution function (PDF) measurements, which highlighted changes in the intermolecular distances due to a rearrangement of the crystal packing upon vapochromic transition. A reaction coordinate describing the structural changes was extracted for each compound by multivariate analysis applied to PDF data. It contributed to the study of the kinetics of the structural changes related to the vapochromic transition, revealing its dependence on the transition metal ion. Instead, the ligand influences the critical temperature, higher for ppy than for bzq, and the inclination of the molecular planes with respect to the unit cell planes, higher for bzq than for ppy. The first stage of water loss triggers a unit cell contraction, determined by the increase in the b axis length and the decrease in the a (for ppy) or c (for bzq) axis lengths. Consequent interplane distance variations and in-plane roto-translations weaken the π-stacking of the room-temperature structure and modify the distances and angles of Pt(II)/Pd(II) chains. The curve describing the intermolecular Pt(II)/Pd(II) distances as a function of temperature, validated by X-ray absorption spectroscopy, was found to reproduce the coordinate reaction determined by the model-free analysis.This research has been supported by the short-term mobility program of the National Research Council (CNR) of Italy and by the Spanish Ministerio de Economía y Competitividad (Ministerio de Ciencia Innovación y Universidades)/FEDER (Project PGC2018-094749-B-I00).Peer reviewe

Solid solution polymorphs afford two high-soluble co-drug forms of tolbutamide and chlorpropamide

The search for solid solutions of class-two insulin secretagogues, tolbutamide and chlorpropamide, reveals a rare case of monotropic polymorphism for the mixed crystals. At any stoichiometry, two crystal forms are isolated that are kinetically stable at room temperature from a few months to over a year. Dissolution tests certify the solubility advantage of the solid solutions over the pure drugs as well as their physical mixture, suggesting a potential application as a highly soluble co-drug formulation.</p

One Molecule, Four Colors: Discovering the Polymorphs of a Thieno(bis)imide Oligomer

The crystallization of 2,2\u2032-(5,5\u2032-(ethyne-1,2-diyl)bis(thiophene-5,2-diyl))bis(5-hexyl-4H-thieno[2,3-c]pyrrole-4,6(5H)-dione), hereafter NTA, in different solvents and/or conditions yielded the identification of five different polymorphs which are characterized by impressive differences in their photophysical behavior. Phase I, phase II, phase III, and phase IV are characterized by a yellow, green, red, and orange emission under illumination with 365 nm light. The crystal structures of phase II and III were determined by single-crystal X-ray diffraction. Phase II is characterized by the elongated molecules that lie parallel to each other in layers and hence by the presence of a long axis in the cell parameters. The two thienoimide-thiophene systems do not lie in the same plane which is consistent with the higher energy emission. In phase III, the NTA molecules pile up and form columns with strong \u3c0-\u3c0 interactions. The packing is consistent with the presence of red emission and the absence of a long axis in the cell parameters. The thermal characterization revealed that phase I, II, and III converts into phase IV, which, upon melting, recrystallizes in the elusive phase V. Quantum-chemical studies were carried out to investigate optical and charge transport properties. Promising charge transport properties with a dominant n-type character were predicted; however, the role of internal conformational disorder could influence the efficiency of charge transport. \ua

AgX-based hybrid coordination polymers: mechanochemical synthesis, structure and luminescence property characterization

Hybrid coordination polymers are interesting for their ability to converge the properties of both inorganic and organic systems in one single compound and recently attention has been focused on silver based hybrid coordination polymers due to their luminescence properties. We searched the CSD to establish the propensity of AgXL (X = Cl−, Br− and I−) with L as an organic ligand to form hybrid coordination polymers. About 800 AgXL structures are deposited in the CSD, with huge structural variability: indeed, it is possible to recognize some structural preferences based on the halide nature. The formation of an inorganic polymeric unit is favoured by iodide but it is also possible with the other halides. This research continues with the synthesis of AgX (X = I−, Br−) based coordination polymers with 2-, 3- and 4-picolylamine (n-pica) as ligands. By mechanochemical synthesis five new hybrid coordination polymers and one coordination polymer have been obtained and their structures determined. While [(AgI)(n-pica)]n are not luminescent, [(AgBr)(n-pica)]n emit and their profile depends on the crystallinity of the sample. © 2023 The Royal Society of Chemistry.</p

Co-crystalline solid solution affords a high-soluble and fast-absorbing form of praziquantel

Praziquantel (PZQ) is a chiral class-II drug, and it is used as a racemate for the treatment of schistosomiasis. The knowledge of several cocrystals with dicarboxylic acids has prompted the realization of solid solutions of PZQ with both enantiomers of malic acid and tartaric acid. Here, the solid form landscape of such a six-component system has been investigated. In the process, two new cocrystals were structural-characterized and three non-stoichiometric, mixed crystal forms identified and isolated. Thermal and solubility analysis indicates a fourfold solubility advantage for the newly prepared solid solutions over the pure drug. In addition, a pharmacokinetic study was conducted in rats, which involved innovative mini-capsules for the oral administration of the solid samples. The available data indicate that the faster dissolution rate of the solid solutions translates in faster absorption of the drug and helps maintain a constant steady-state concentration.</p

Tuning polymorphism in 2,3-thienoimide capped oligothiophene based field-effect transistors by implementing vacuum and solution deposition methods

We report on the investigation of the influence of the molecular packing and film morphology on the field-effect charge mobility in 2,3-thienoimide-based oligothiophenes semiconductors (Cn-NT4N). Organic field-effect transistors are realized by implementing both vacuum and solution methods in order to control the solid-state phase of the active layer. Thermal sublimation in a high vacuum chamber and supersonic molecular beam deposition were used as vacuum-based fabrication approaches for preparing thin films, while lithographically controlled wetting was used, as a solution-deposition technique, for the fabrication of the microstructured films. Thermal sublimation leads to thin films with a phase packing showing ambipolar behaviour, while supersonic molecular beam deposition enables, by varying the deposition rate, the formation of two different crystal phases, showing ambipolar and unipolar field-effect behaviours. On the other hand, lithographically controlled wetting enables the formation of Cn-NT4N microstructured active layers and their implementation in field-effect transistors