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

ABSTRACT 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.