Mechanochromic luminescence (MCL) materials have a high requirement in high-tech applications such as pressure sensors and data storage. Nevertheless, the diversity of these emitters was still rather restricted owing to...

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Scheme 1. The molecular design strategy for B/N nanographenes and their calculated racemization barrier (see text for detail).

Dinuclear Pt­(III) complexes were commonly reported to have short-lived lowest-lying triplet states, resulting in extremely weak or no photo­lumin­escence. To overcome this obstacle, a new series of dinuclear Pt­(III) complexes, named Pt2a-Pt2c, were strategically designed and synthesized using donor (D)–acceptor (A)-type oxadiazole-thiol chelates as bridging ligands. These dinuclear Pt­(III) complexes possess a d7–d7 electronic configuration and exhibit intense phosphorescence under ambient conditions. Among them, Pt2a exhibits orange phosphorescence maximized at 618 nm in degassed dichloromethane solution (Φp ≈ 8.2%, τp ≈ 0.10 μs) and near-infrared (NIR) emission at 749 nm (Φp ≈ 10.1% τp ≈ 0.66 μs) in the crystalline powder and at 704 nm (Φp ≈ 33.1%, τp ≈ 0.34 μs) in the spin-coated neat film. An emission blue-shifted by more than 3343 cm–1 is observed under mechanically ground crystalline Pt2a, affirming intermolecular interactions in the solid states. Time-dependent density functional theory (TD-DFT) discloses the lowest-lying electronic transition of Pt2a-Pt2c complexes to be a bridging ligand–metal–metal charge transfer (LMMCT) transition. The long-lived triplet states of these dinuclear platinum­(III) complexes may find potential use in lighting. Employing Pt2a as an emitter, high-performance organic light-emitting diodes (OLEDs) were fabricated with NIR emission at 716 nm (η = 5.1%), red emission at 614 nm (η = 8.7%), and white-light emission (η = 11.6%) in nondoped, doped (in mCP), and hybrid (in CzACSF) devices, respectively.

The correlation between molecular packing structure and its room-temperature phosphorescence (RTP), hence rational promotion of the intensity, remains unclear. We herein present racemism enhanced RTP chiral chromophores by 2,2-bis-(diphenylphosphino)-1,1-napthalene (rac-BINAP) in comparison to its chiral counterparts. The result shows that rac-BINAP in crystal with denser density, consistent with a long standing Wallach’s rule, exhibits deeper red RTP at 680 nm than that of the chiral counterparts. The cross packing between alternative R- and S- forms in rac-BINAP crystal significantly retards the bimolecular quenching pathway, triplet-triplet annihilation (TTA), and hence suppresses the non-radiative pathway, boosting the RTP intensity. The result extends the Wallach’s rule to the fundamental difference in chiral-photophysics. In electroluminescence, rac-BINAP exhibits more balanced fluorescence versus phosphorescence intensity by comparison with that of photoluminescence, rendering a white-light emission. The result paves an avenue en route for white-light organic light emitting diodes via full exploitation of intrinsic fluorescence and phosphorescence.