Influence of regioisomerism in bis(terpyridine) based exciplexes with delayed fluorescence

A. L. S. acknowledges financial support through a Cusanuswerk scholarship. The authors acknowledge support by the state of Baden-Württemberg through bwHPC and the German Research Foundation (DFG) through grant no INST 40/575-1 FUGG (JUSTUS and JUSTUS 2 cluster). M. C. G. acknowledges support from the Leverhulme Trust (RPG-2016047) and the Alexander von Humboldt Stiftung through the Humboldt-Professorship. A. M. acknowledges support from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 101023743 (PolDev). C. B. acknowledges funding by the BMBF and the Ministry of Culture and Science of the German State of North Rhine-Westphalia (MKW) under the Excellence Strategy of the Federal Government and the Länder.Exciplexes of individual electron donor and acceptor molecules are a promising approach to utilizing otherwise non-emissive triplet states in optoelectronic applications. In this work, we synthesize a series of bis(terpyridine) pyrimidine (BTP) isomers and employ them as electron acceptors in complexes with tris(4-carbazoyl-9-ylphenyl)amine (TCTA). We show that these TCTA : BTP complexes produce thermally activated delayed fluorescence (TADF) by exciplex emission, and we investigate the influence of the nitrogen position in the pyridine on the optical and electronic properties of the exciplex. The molecular arrangement of the complex is studied using scanning tunneling microscopy (STM) as well as classical force field and density functional theory (DFT) simulations. Finally, we fabricate organic light-emitting diodes (OLEDs) with maximum external quantum efficiencies ranging between 0.5% and 2% – depending on the BTP isomer.PostprintPostprintPeer reviewe

Attenuated sensing of SHH by <i>Ptch1</i> underlies evolution of bovine limbs

The large spectrum of limb morphologies reflects the wide evolutionary diversification of the basic pentadactyl pattern in tetrapods. In even-toed ungulates (artiodactyls, including cattle), limbs are adapted for running as a consequence of progressive reduction of their distal skeleton to symmetrical and elongated middle digits with hoofed phalanges. Here we analyse bovine embryos to establish that polarized gene expression is progressively lost during limb development in comparison to the mouse. Notably, the transcriptional upregulation of the Ptch1 gene, which encodes a Sonic hedgehog (SHH) receptor, is disrupted specifically in the bovine limb bud mesenchyme. This is due to evolutionary alteration of a Ptch1 cis-regulatory module, which no longer responds to graded SHH signalling during bovine handplate development. Our study provides a molecular explanation for the loss of digit asymmetry in bovine limb buds and suggests that modifications affecting the Ptch1 cis-regulatory landscape have contributed to evolutionary diversification of artiodactyl limbs