Aggregation induced emission and mechanochromic luminescence by cyanostilbene-based organic luminophores

In this manuscript, we report novel cyanostilbene based luminogens, 1CF3 and 1F2 that exhibit pronounced “aggregation induced emission” (AIE) characteristics and mechanochromic luminescence (MCL) switching in solid state. A poorly emissive methanol solution of 1CF3 or 1F2 can be highly emissive after addition of poor solvent. Our morphological study reveals that the molecules self-assemble to higher crystalline state at during AIE process. When the single crystals of 1CF3 or 1F2 were subjected to mechanical pressure, a prominent mechanochromic switching from greenish yellow emission to red emission was observed. The red emissive material can be switched back to its initial greenish yellow emissive material by solvent vapour fumigation. Powder X-ray diffraction and single crystal X-ray diffraction study revealed that the mechanochromic colour switching is due to the packing change induced by mechanical pressure. The practical applicability of the MCL materials was demonstrated for ink-free writing and solvent vapour erasing.