Substitution of 1,3,6,8-tetraethynylpyrene with sterically bulky trimethylsilyl groups enabled four modes of molecular packing, two polymorphs (triclinic system (Y-form) and "loose" crystal Col ho (O K -form)), a "rigid" liquid crystalline phase Col ho (O C -form), and an amorphous phase (O A -form), which emitted fluorescence at different wavelengths under UV light. The four phases could be interconverted by physical stimuli such as heating, grinding by mortar and pestle, and exposing to the vapor of organic solvents.
Lewis acid La(OTf) 3 -catalyzed chemoselective cyclization of hydroxyl substituted ethylenediamine derivatives with aldehydes has been described for the first time, which provides efficient access to diversely functionalized 1,3-imidazolidines and 3,1-benzoxazines in generally good yields only by adjusting the position of the methylene group within hydroxyl substituted ethylenediamines. The reaction is suitable to aromatic aldehydes and aliphatic ones. Plausible mechanisms are also proposed to explain the observed reaction modes, wherein the nucleophilicity of nitrogen and oxygen atoms plays an important role in controlling the chemoselectivity.
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