Intramolecular hydrogen bonding-induced conformation-locked multifunctional emitters for non-doped OLEDs

Organic multifunctional triplet-harvesting emitters based organic light emitting diodes (OLEDs) are a relatively unexplored area, primarily due to the challenging requirements of achieving high rates of intersystem crossing (ISC; k(ISC) > 10(7) s(-1)), reverse intersystem crossing (RISC; k(RISC) > 10(6) s(-1)), radiative decay (k(r) > 10(7) s(-1)), and low non-radiative decay (k(nr) < 10(6) s(-1)) within non-doped systems. In this study, we synthesized three asymmetric heavy-atom-free (HAF) multifunctional triplet-harvesting emitters. The incorporation of intramolecular hydrogen bonding (IHB) induced conformational locking and distortion, resulting in a quasi-planar structure that effectively reduces reorganization energy (lambda). Consequently, Qx-Py-2DMAC exhibited improved radiative characteristics with high quantum yields (0.94) in neat film state. Significantly, the existence of IHB interactions was confirmed through various methods, including DFT calculations, single-crystal XRD, and 2D-GIWAXD measurements, which verified the effect in both single molecules and solid states. Subsequently, the IHB-induced conformation-locked structure exhibited a preferred orientation with a large coherence length (L-c) for dense packing and efficient emission in aggregated state. Consequently, due to the IHB-induced unique aggregation properties, Qx-Py-2DMAC realized significant multifunctionality of aggregation-induced emission (AIE), mechanochromic luminescence (MCL), thermally activated delayed fluorescence (TADF), and room-temperature phosphorescence (RTP) in solid state. In this regard, non-doped OLEDs were successfully realized.

Automated summary

In this study, three asymmetric heavy-atom-free multifunctional triplet-harvesting emitters were synthesized, and the optimized radiative characteristics were achieved through the incorporation of intramolecular hydrogen bonding. The intramolecular hydrogen bonding also enabled various emission properties, such as aggregation-induced emission, mechanochromic luminescence, thermally activated delayed fluorescence, and room-temperature phosphorescence, in the solid state.