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Figure 1
Chemical structures (i), (ii) and (iii) of the compounds (1), molecular crystals of the three individual compounds illuminated under UV (2), their qualitative deformation behaviour upon mechanical action (3), and mechanochromic luminescence behaviour of the crystals upon smearing (4). In column 4, (a), (d) and (g) show the UV (365 nm) emission colour of initial powder films prepared by gently grinding single crystals of the three samples using a mortar and pestle. Images (b), (e) and (h) correspond to the films after firmly scratching the initial films with a pestle, resulting in a colour change from cyan to yellow for BF2dbm(tBu)2 and green to yellow for BF2dbm(OMe)2 while no colour change was observed for BF2dbmOMe at room temperature (h), respectively. For both BF2dbm(tBu)2 and BF2dbm(OMe)2 compounds, the films recover to the parent colour shown in (c) and (f) after a few minutes of heating with a hot-air gun. In the case of BF2dbmOMe the ML experiments were repeated at −98°C by immersing the mortar into frozen methanol by cooling wth liquid N2 (g), but no significant colour change was observed in (h) and (i).

Volume 2| Part 6| September 2015| Pages 611-619
ISSN: 2052-2525