MicroRNA (miRNA) are well known to target 3’ untranslated regions (3’UTR) in mRNAs to silence gene expression at post-transcriptional levels. Multiple reports have also indicated the capability of miRNAs to target protein-coding sequences (CDS); however, miRNAs have been generally believed to function in a similar mechanism(s) regardless of the location of their action sites. We herein report a class of miRNA recognition elements (MREs) that exclusively function in CDS regions in humans. Through functional and mechanistic characterization of these “unusual” MREs, we demonstrate that CDS-targeted miRNAs require extensive base pairings in the 3’ side rather than the 5’ seed; cause gene silencing in an Argonaute-dependent, but GW182-independent manner; and repress translation by inducing transient ribosome stalling instead of mRNA destabilization. These findings reveal distinct mechanisms and functional consequences for miRNAs to target CDS versus 3’UTR and suggest that CDS-targeted miRNAs may enlist a translational quality control (QC)-related mechanism to regulate translation in mammalian cells.

A series of bipolar transport host materials: 2,5‐bis(2‐(9H‐carbazol‐9‐yl)phenyl)‐1,3,4‐oxadiazole (o‐CzOXD) (1), 2,5‐bis(4‐(9H‐carbazol‐9‐yl)phenyl)‐1,3,4‐oxadiazole (p‐CzOXD) (2), 2,5‐bis(3‐(9H‐carbazol‐9‐yl)phenyl)‐1,3,4‐oxadiazole (m‐CzOXD) (3) and 2‐(2‐(9H‐carbazol‐9‐yl)phenyl)‐5‐(4‐(9H‐carbazol‐9‐yl)phenyl)‐1,3,4‐oxadiazole (op‐CzOXD) (4) are synthesized through simple aromatic nucleophilic substitution reactions. The incorporation of the oxadiazole moiety greatly improves their morphological stability, with Td and Tg in the range of 428–464 °C and 97–133 °C, respectively. The ortho and meta positions of the 2,5‐diphenyl‐1,3,4‐oxadiazole linked hybrids (1 and 3) show less intramolecular charge transfer and a higher triplet energy compared to the para‐position linked analogue (2). The four compounds exhibit similar LUMO levels (2.55–2.59 eV) to other oxadiazole derivatives, whereas the HOMO levels vary in a range from 5.55 eV to 5.69 eV, depending on the linkage modes. DFT‐calculation results indicate that 1, 3, and 4 have almost complete separation of their HOMO and LUMO levels at the hole‐ and electron‐transporting moieties, while 2 exhibits only partial separation of the HOMO and LUMO levels possibly due to intramolecular charge transfer. Phosphorescent organic light‐emitting devices fabricated using 1–4 as hosts and a green emitter, Ir(ppy)3 or (ppy)2Ir(acac), as the guest exhibit good to excellent performance. Devices hosted by o‐CzOXD (1) achieve maximum current efficiencies (ηc) as high as 77.9 cd A−1 for Ir(ppy)3 and 64.2 cd A−1 for (ppy)2Ir(acac). The excellent device performance may be attributed to the well‐matched energy levels between the host and hole‐transport layers, the high triplet energy of the host and the complete spatial separation of HOMO and LUMO energy levels.

Two series of polyurethanes (P1-P10) containing NLO chromophores as side chains were prepared, in which the size of isolation groups was changed from small atoms to much larger groups such as carbazolyl groups. The polymers were well characterized. The tested NLO properties of the polymers demonstrate that the NLO values and the poling efficiency of the polymers are not always improved with increasing of the size of isolation spacer, and for a given chromophore moiety, there is a suitable isolation group present to boost its microscopic β value to possibly higher macroscopic NLO property efficiently.

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