Packing-dependent polymorphism: A stimuli-responsive macrocyclic diketopyrrolopyrrole

Abstract

In the present work, a 12C-long-alkyl ring substituted diketopyrrolopyrrole (DPP), namely compound 1, was prepared. According to the differently oriented rings, there are two enantiomers 1a and 1b. Compound 1 is found to have reversible mechano- and thermochromism, with a drastic fluorescence quantum yield switch between 61% and 3%, making it an ideal candidate for stimuli-responsive materials. Further investigation has evidenced that, compound 1 exists in two polymorphic forms and the molecules in both forms take nearly the same conformation. The chromism is thus triggered by molecular packing alternation corresponding to those two polymorphs upon mechano- or thermo-stimulus. This is a rare example of chromic phenomenon caused by different packing of two enantiomers rather than their conformational difference.