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A new class of carbene–anilido boron complexes have been designed and synthesized. The complexes show intense fluorescence with large Stokes shift because of their charge-transfer excited states, different from typical BODIPY dyes. By using a chiral 1,1′-bi(2-naphthol) ligand, dyes exhibiting circularly polarized luminescence can also be facilely developed. [ABSTRACT FROM AUTHOR]

Although phosphorescent Pt(II) complexes have shown great potential for organic light-emitting diodes (OLEDs), red phosphorescence with a high photoluminescence quantum yield (PLQY) and a short emission lifetime is still scarce because of the limitation on the radiative decay rate. Transition metal complexes have proved advantageous for emitting thermally activated delayed fluorescence (TADF), but TADF Pt(II) complexes have rarely been reported. Herein, we describe the design and synthesis of two red TADF Pt(II) complexes, namely Pt-tCzDBPZ (Pt1) and Pt2-tCzDBPZ (Pt2). By using a donor–acceptor type monodentate ligand, the complexes have metal-perturbed intraligand charge-transfer (MPICT) excited states featuring small singlet–triplet energy gaps (0.086–0.089 eV) and a moderately large spin–orbit coupling matrix element (∼10 cm−1). The complexes exhibit red TADF emissions (ca. 630 nm) with high PLQYs of 82–92% and delayed fluorescence lifetimes of 1.51–1.63 μs. The vacuum-deposited red OLEDs based on Pt-tCzDBPZ show high external quantum efficiencies of up to 35.6% and small roll-offs. In spite of the significant heavy atom effect of Pt for facilitating phosphorescence, this study demonstrates a feasible design of Pt(II)–TADF emitters which can enable them to outperform phosphorescent Pt(II) complexes. [ABSTRACT FROM AUTHOR]

"Carbene–metal(I)–amide" (CMA) complexes have garnered significant attention due to their remarkable properties and potential TADF applications in organic electronics. However, the atomistic working mechanism is still elusive. Herein, we chose two CMA complexes, i.e., cyclic (alkyl)(amino) carbene–copper[gold](I)–carbazole (CAAC–Cu[Au]–Cz), and employed both DFT and TD-DFT methods, in combination with radiative and nonradiative rate calculations, to investigate geometric and electronic structures of these two complexes in the ground and excited states, including orbital compositions, electronic transitions, absorption and emission spectra, and the luminescence mechanism. It is found that the coplanar or perpendicular conformations are coexistent in the ground state (S0), the lowest excited singlet state (S1), and the triplet state (T1). Both the coplanar and perpendicular S1 and T1 states have similar ligand-to-ligand charge transfer (LLCT) character between CAAC and Cz, and some charge-transfer character between metal atoms and ligands, which is beneficial to minimize the singlet–triplet energy gaps (ΔEST) and increase the spin–orbit coupling (SOC). An interesting three-state (S0, S1, T1) model involving two regions (coplanar and perpendicular) is proposed to rationalize the experimental TADF phenomena in the CMA complexes. In addition to the coplanar ones, the perpendicular S1 and T1 states also play a role in promoting the repopulation of the coplanar S1 exciton, which is a primary source for the delayed fluorescence. [ABSTRACT FROM AUTHOR]