Elastic Organic Crystals of Semiconducting Hydrocarbon Fully π‐Conjugated Molecules for Efficient Flexible Ultra‐Deep‐Blue Amplified Spontaneous Emission Waveguides

Efficient ultra-deep-blue light-emitting elastic organic crystals are promising candidates for flexible optoelectronics owing to their low defect density, regular intermolecular packing, and excellent mechanical stability. However, heteroatom-containing fully π-conjugated molecules (FπCMs) often undergo strong π-π stacking, leading to pronounced intramolecular π-electron hybridization and intermolecular charge-transfer interactions. These effects can induce nonradiative decay and redshifted emission, which are unfavorable for deep-blue device applications. Herein, we report an efficient ultra-deep-blue light-emitting elastic molecular crystal based on hydrocarbon semiconducting fully π-conjugated ter(9,9-diarylfluorene)s (DM3C8; molecular weight > 1300 g/mol), enabling flexible ultra-deep-blue amplified spontaneous emission (ASE) waveguides. Benefiting from the synergistic effects of flexible side chains and bulky steric hindrance, DM3C8 elastic crystals exhibit outstanding ultra-deep-blue emission with CIE coordinates of (0.16, 0.06) and a photoluminescence efficiency of ∼51%. This performance is attributed to single-chromophore emission with suppressed π-π interactions. The unique piezochromic emission behavior of DM3C8 elastic crystals is further investigated, revealing reversible and dynamic intermolecular networks. Finally, DM3C8 elastic crystals function as low-threshold flexible ultra-deep-blue ASE optical waveguides, exhibiting low optical loss coefficients in both straight (α < 0.07 db/mm) and bent (α < 0.08 db/mm) configurations. These results indicate that short-range structural perturbations have minimal impact on optical propagation.