Exploring the Early Time Behavior of the Excited States of an Archetype Thermally Activated Delayed Fluorescence Molecule.

Optical pump-probe techniques allow for an in-depth study of dark excited states. Here, we utilize them to map and gain insights into the excited states involved in the thermally activated delayed fluorescence (TADF) mechanism of a benchmark TADF emitter DMAC-TRZ. The results identify different electronic excited states involved in the key TADF transitions and their nature by combining pump-probe and photoluminescence measurements. The photoinduced absorption signals are highly dependent on polarity, affecting the transition oscillator strength but not their relative energy positions. In methylcyclohexane, a strong and vibronically structured local triplet excited state absorption (3LE → 3LEn) is observed, which is quenched in higher polarity solvents as 3CT becomes the lowest triplet state. Furthermore, ultrafast transient absorption (fsTA) confirms the presence of two stable conformers of DMAC-TRZ: (1) quasi-axial (QA) interconverting within 20 ps into (2) quasi-equatorial (QE) in the excited state. Moreover, fsTA highlights how sensitive excited state couplings are to the environment and the molecular conformation.

Role of Torsional Flexibility in the Film Formation Process in Two π-Conjugated Model Oligomers.

The performance of solution-processed organic semiconductor devices is heavily influenced by the morphology of the active layer. Film formation is a complex process, with the final morphology being the result of the interplay between processing parameters and molecular properties, which is only poorly understood. Here, we investigate the influence of molecular stiffness by using two model oligomers, TT and CT, which differ only in the rotational flexibility of their central building block. We monitor absorption and emission simultaneously in situ during spin coating. We find that film formation takes place in four similar stages for both compounds. However, the time scales are remarkably different during the third stage, where electronically interacting aggregates are created. While this process is fast for the stiff CT, it takes minutes for the flexible TT. By comparing with previously determined aggregation properties in solution, we conclude that even though aggregate formation concurs with a planarization process, a certain amount of backbone flexibility is beneficial for establishing ordered structures during film formation. Here, the elongated time window in the case of the flexible compound can further allow for better processing control.

Setup to Study the in Situ Evolution of Both Photoluminescence and Absorption during the Processing of Organic or Hybrid Semiconductors.

In situ measurement techniques, applied during the solution processing of novel semiconductors such as organic semiconductors or hybrid perovskites, have become more and more important to understand their film formation. In that context, it is crucial to determine how the optical properties, namely photoluminescence (PL) and absorption, evolve during processing. However, until now PL and absorption have mostly been investigated independently, significantly reducing the potential insights into film formation dynamics. To tackle this issue we present the development of a detection system that allows simultaneous measurement of full absorption and PL spectra during solution processing of the investigated film. We also present a spin-coater system attachable to the detection system, where the temperature of the substrate on which the film is processed can be changed. We performed test measurements by spin coating the well-known conjugated polymer P3HT demonstrating the potential of this technique. By considering absorption and corresponding PL, we extract the PL quantum yield (PLQY) during processing, which decreases with substrate temperature. Furthermore, we identify a significant red shift of the PL just prior to the onset of the aggregation process, indicating the importance of chain planarization prior to solid film formation.

Treatment outcome in angle class II, division 1 patients in pre-puberty and puberty after jumping-the-bite appliance.

AIM: The aim of this study was to investigate whether, and if so, to what extent, skeletal and dento-alveolar developments of the stomatognathic system take a different course due to influence of Tränkmann's jumping-the-bite appliance (JTB) in pre-pubertal and pubertal patients in comparison to untreated control groups presenting the same conditions at baseline. We aim to discover whether the results are better when the device is used on prepubertal children, or those in puberty. PATIENTS AND METHODS: Two lateral cephalograms were scanned in treated children presenting Angle Class II, Division 1 malocclusion; they were scanned in untreated children with the same distoclusion at intervals between at least 11 months and at most 25 months. The same procedure was taken in children in pre-puberty (female, min. = 8.6 yrs, max. = 11 yrs; male, min. = 9 yrs, max. = 12.6 yrs) and in puberty (female, min. = 11 yrs, max. = 14 yrs; male, min. = 12.6 yrs, max. = 15 yrs). The cephalometric analysis was made with the orthodontics-PC-program Onyx Ceph (Image Instruments, Chemnitz, Germany) using a modified Bergen/Hasund analysis [7, 8]. RESULTS: The Angle Class II, Division 1 malocclusion of all treated patients evolved into an Angle Class I occlusion via Tränkmann's JTB design. The location of this transformation was mainly dento-alveolar in both pre-puberty and puberty. The differences between the control and JTB groups concerning the development of cephalometric values in pre-pubertal age were unremarkable if one considers the range of reading error. The exception to this was with angleUP1-NA, which increased more in the control group than in the treated group. angleSNB, arB (mm), angleANB and angleML-NSL showed greater change in the targeted direction in the control group than in the JTB group in pubertal patients. The increase in the arA length (mm) was clearly, but not statistically significantly, inhibited by the JTB in puberty. Comparing both treated groups, one can conclude that cephalometric values developed more favorably in the pre-pubertal than in the pubertal patients, with the exception of angleSNA.