On the crystal forms of NDI-C6: annealing and deposition procedures to access elusive polymorphs

NDI-C6 has been extensively studied for its semiconducting properties and its processability. It is known to have several polymorphs and a high thermal expansion. Here we report the full thermal characterization of NDI-C6 by combining differential scanning calorimetry, variable temperature X-ray powder diffraction, and hot stage microscopy, which revealed two different thermal behaviours depending on the annealing process. The ranking of stability was determined by the temperature and energy involved in the transitions: Form alpha is stable from RT up to 175 degrees C, Form beta is metastable at all temperatures, Form gamma is stable in the range 175-178 degrees C, and Form delta in the range 178-207 degrees C followed by the melt at 207 degrees C. We determined the crystal structure of Form gamma at 54 degrees C from powder. The analysis of the thermal expansion principal axis shows that Form alpha and Form gamma possess negative thermal expansion (X1) and massive positive thermal expansion (X3) which are correlated to the thermal behaviour observed. We were able to isolate pure Form alpha, Form beta, and Form gamma in thin films and we found a new metastable form, called Form epsilon, by spin coating deposition of a toluene solution of NDI-C6 on Si/SiO2 substrates

Polymorph Separation by Ordered Patterning

We herein address the problem of polymorph selection by introducing a general and straightforward concept based on their ordering. We demonstrated the concept by the ordered patterning of four compounds capable of forming different polymorphs when deposited on technologically relevant surfaces. Our approach exploits the fact that, when the growth of a crystalline material is confined within sufficiently small cavities, only one of the possible polymorphs is generated. We verify our method by utilizing several model compounds to fabricate micrometric "logic patterns" in which each of the printed pixels is easily identifiable as comprising only one polymorph and can be individually accessed for further operations

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

From synthesis to device fabrication: elucidating the structural and electronic properties of C7-BTBT-C7

We report the polymorph investigation, crystallographic study and fabrication of organic field-effect transistors (OFETs) in solution-processed thin films of a prototypical organic semiconductor, i.e., 2,7-diheptylbenzo[b]benzo[4,5]thieno[2,3-d]thiophene (C7-BTBT-C7). We found that this molecule self-assembles solely into one type of stable crystal form, regardless of the experimental conditions employed when using conventional and non-conventional methods of crystallization. The integration of blends of C7-BTBT-C7 with polystyrene as active materials in OFETs fabricated using a solution shearing technique led to a field-effect mobility of 1.42 ± 0.45 cm2 V−1 s−1 in the saturation regime when a coating speed of 10 mm s−1 was employed. The intrinsic structural properties control the overlap of the frontier orbitals, thereby affecting the device performance. The interplay between the crystal packing, thin film morphology and uniformity and its impact on the device performance are reported.We acknowledge the Paul Scherrer Institut, Villigen, Switzerland, for the provision of synchrotron radiation beam time at the beamline MS-X04SA of the SLS (ID proposal 20201790). P. P., L. F., N. M., N. T., J. C., P. S., M. M. T., Y. G., E. M., and L. M., contributors of the paper, are the members of the UHMob project. This work has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant no. 811284. G. S. is a FNRS Research Associate (Belgian National Fund for Scientific Research). G. S. acknowledges financial support from the Francqui Foundation (Francqui Start-Up Grant). G. S. thanks the FNRS for financial support through the research project COHERENCE2 (no. F.4536.23). M. M. T. and L. F. also acknowledge MCIN through the project GENESIS PID2019 and the “Severo Ochoa” Programme for Centers of Excellence in R&D (FUNFUTURE CEX2019-000917-S), and the Generalitat de Catalunya (2017-SGR-918).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Development of EULAR recommendations for the reporting of clinical trial extension studies in rheumatology

Objectives: Our initiative aimed to produce recommendations on post-randomised controlled trial (RCT) trial extension studies (TES) reporting using European League Against Rheumatism (EULAR) standard operating procedures in order to achieve more meaningful output and standardisation of reports. Methods: We formed a task force of 22 participants comprising RCT experts, clinical epidemiologists and patient representatives. A two-stage Delphi survey was conducted to discuss the domains of evaluation of a TES and definitions. A ‘0–10’ agreement scale assessed each domain and definition. The resulting set of recommendations was further refined and a final vote taken for task force acceptance. Results: Seven key domains and individual components were evaluated and led to agreed recommendations including definition of a TES (100% agreement), minimal data necessary (100% agreement), method of data analysis (agreement mean (SD) scores ranging between 7.9 (0.84) and 9.0 (2.16)) and reporting of results as well as ethical issues. Key recommendations included reporting of absolute numbers at each stage from the RCT to TES with reasons given for drop-out at each stage, and inclusion of a flowchart detailing change in numbers at each stage and focus (mean (SD) agreement 9.9 (0.36)). A final vote accepted the set of recommendations. Conclusions: This EULAR task force provides recommendations for implementation in future TES to ensure a standardised approach to reporting. Use of this document should provide the rheumatology community with a more accurate and meaningful output from future TES, enabling better understanding and more confident application in clinical practice towards improving patient outcomes