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Two multifunctional emissive molecules (QBP‐DMAC and QBP‐PXZ) with a novel accepting unit (5,6‐dihydropyrrolo[2,1‐a]isoquinoline‐1,3‐diyl)bis(phenylmethanone) (QBP) are designed and synthesized. Both emitters exhibit thermally activated delayed fluorescence (TADF) and aggregation‐induced emission characteristics, and QBP‐DMAC shows multicolor mechanochromic luminescent (MCL). Intriguingly, crystal structure of QBP‐DMAC reveals loose molecular packing mode and slipped π–π intramolecular interactions between DMAC moieties, which are identified as the underlying mechanism for its MCL behavior. Moreover, the QBP‐DMAC‐based organic light‐emitting diode device achieves high external quantum efficiencies up to 18.8%, which is among the highest efficiencies for the MCL‐active TADF emitters.