Effect of substituting non-polar chains with polar chains on the structural dynamics of small organic molecule and polymer semiconductors

The processability and optoelectronic properties of organic semiconductors can be tuned and manipulated via chemical design. The substitution of the popular alkyl side chains by oligoethers has recently been successful for applications such as bioelectronic sensors and photocatalytic hydrogen evolution. Beyond the differences in polarity, the carbon–oxygen bond in oligoethers is likely to render the system softer and more prone to dynamical disorder that can be detrimental to charge transport for example. In this context, we use neutron spectroscopy as a master method of probe, in addition to characterisation techniques such as X-ray diffraction, differential scanning calorimetry and polarized optical microscopy to study the effect of the substitution of n-hexyl (Hex) chains by triethylene glycol (TEG) chains on the structural dynamics of two organic semiconducting materials: a phenylene–bithiophene–phenylene (PTTP) small molecule and a fluorene-co-dibenzothiophene (FS) polymer. Counterintuitively, inelastic neutron scattering (INS) reveals a general softening of the modes of PTTP and FS materials with Hex chains, pointing towards an increased dynamical disorder in the Hex-based systems. However, temperature-dependent X-ray and neutron diffraction as well as INS and differential scanning calorimetry evidence an extra reversible transition close to room temperature for PTTP with TEG chains. The observed extra structural transition, which is not accompanied by a change in birefringence, can also be observed by quasi-elastic neutron scattering (QENS). A fastening of the TEG chains dynamics is observed in the case of PTTP and not FS. We therefore assign this transition to the melt of the TEG chains. Overall the TEG chains are promoting dynamical order at room temperature, but if crystallising, may introduce an extra reversible structural transition above room temperature leading to thermal instabilities. Ultimately, a deeper understanding of chain polarity and structural dynamics can help guide new materials design and navigate the intricate balance between electronic charge transport and aqueous swelling that is being sought for a number of emerging organic electronic and bioelectronic applications

Role of oxygen within end group substituents on film morphology and charge carrier transport in thiophene/phenylene small-molecule semiconductors

In this study, the end group polarity of (5,5′)-biphenyl-(2,2’)-bithiophenes (PTTPs) was systematically varied from alkyl (1) to alkoxy (2) with one oxygen atom to glycol (3) with two oxygen atoms while the overall length of the end groups is kept constant. Thin films of the three compounds were sublimated at different substrate temperatures and their morphology, crystallinity and charge carrier transport in field-effect transistors was investigated to draw structure-property relationships for the PTTP derivatives. For all three compounds, the effective charge carrier mobility is improved with higher substrate temperatures at which films with higher crystallinity and larger grains are formed. The effective mobility decreases with higher polarity of the end groups from alkyl to alkoxy and glycol. The reliability factor of the alkyl (1) and alkoxy (2) substituted PTTPs decreases with higher substrate temperature, but at the same time this value is enhanced for the glycol substituted molecules (3). The transistors of 3 prepared at higher substrate temperatures also show a reduced threshold voltage and smaller hysteresis in the transfer characteristics. These insights are important for the understanding of the impact of oxygen incorporation into side chain/end group substituents of organic semiconductors and their implementation in organic electrochemical transistors, thermoelectrics and photovoltaics

Mixed Ionic and Electronic Conduction in Small-Molecule Semiconductors.

Small-molecule organic semiconductors have displayed remarkable electronic properties with a multitude of π-conjugated structures developed and fine-tuned over recent years to afford highly efficient hole- and electron-transporting materials. Already making a significant impact on organic electronic applications including organic field-effect transistors and solar cells, this class of materials is also now naturally being considered for the emerging field of organic bioelectronics. In efforts aimed at identifying and developing (semi)conducting materials for bioelectronic applications, particular attention has been placed on materials displaying mixed ionic and electronic conduction to interface efficiently with the inherently ionic biological world. Such mixed conductors are conveniently evaluated using an organic electrochemical transistor, which further presents itself as an ideal bioelectronic device for transducing biological signals into electrical signals. Here, we review recent literature relevant for the design of small-molecule mixed ionic and electronic conductors. We assess important classes of p- and n-type small-molecule semiconductors, consider structural modifications relevant for mixed conduction and for specific interactions with ionic species, and discuss the outlook of small-molecule semiconductors in the context of organic bioelectronics

Die Wirkung psychologischer Spiele auf die mentale Gesundheit in der Erziehung

The percentage of those who have mental health problems is much higher in the group of people who chose supporting occupations (teachers, psychologists, etc.), than in the whole society. Teachers need personal development as psychotherapists do. In Rumania the realisation of such a project would involve many difficulties. Because of a misbelief (education is unidirectional) there is an expectation, indeed a very strong one, that teachers adopt the role of the Rescuer, somebody who tries to solve other people’s problems, even if the other refuses help. Experimental data confirm the tendency of teachers to adopt the role of the Rescuer. Adopting this role can have two negative consequences. 1) It negatively affects the maturation process of the child and 2) it becomes a source of psychological games in which participants make efforts both to suffer and to make others suffer. For prevention, an education for maturation is necessary, which is possible only in assertive conflict solving and in OK–OK life positions. Different psychological schools are analysed. This life position is adopted by humanist psychology and by transactional analysis. The promotion of humanistic psychology or transactional analysis-based pedagogy in Rumania can be helpful, but is not the only solution and is not the solution. The problem is that humanistic Gordon pedagogy is unknown, and there are no certified transactional analysis trainers in Rumania today. Menschen, die mit mentalen Problemen zu kämpfen haben, entscheiden sich häufiger für einen helfenden Beruf (Lehrer, Psychologe etc.). Auch Lehrer benötigen Selbsterfahrung, wie sie für Psychotherapeuten vorgeschrieben ist. Deren Einführung in Rumänien stößt jedoch auf großen Widerstand. Aufgrund des Irrglaubens, Erziehung sei ein unidirektionaler Prozess, stehen die Lehrer unter Druck, die Rolle des Retters zu übernehmen. Ein Retter versucht, nach eigenen Maßstäben die Probleme eines anderen gegen dessen Widerstand zu lösen. Die Ergebnisse von Experimenten bestätigen die Tendenz von Lehrern, als „Retter“ zu handeln. Die Rolle des Retters hat zwei negative Konsequenzen: Sie bremst die Reifung des Kindes und fördert die Entstehung von psychologischen Spielen. Bei diesen Spielen bemühen sich die Partner darum, selbst zu leiden bzw. den Partner leiden zu lassen, daher bedeuten diese eine ernsthafte Gefährdung der mentalen Gesundheit der Schule. Als Vorbeugung wird ein der Reifung des Kindes förderlicher Erziehungsstil verwendet, der nur mit Hilfe des assertiven Umgangs mit Konflikten und einer OK–OK-Haltung möglich ist. Der Autor kommt zu dem Schluss, dass diese Lebenseinstellung inbesondere von der humanistischen Psychologie und der Transaktionsanalyse vertreten wird. Die Einführung einer auf diesen psychologischen Schulen basierenden Pädagogik in Rumänien ist eine verlockende Möglichkeit, aber nicht die einzige und nicht die Möglichkeit. Die Schwierigkeit besteht darin, dass die Gordon-Pädagogik in der rumänischen Fachliteratur unbekannt ist, während die rumänische Transaktionsanalyse noch in den Kinderschuhen steckt