Selective Chirality-Driven Photopolymerization of Diacetylene Crystals.

Crystal engineering of two diacetylene monomers was achieved by branching two chiral groups [R = PhC*MeNH(CO)CH] exhibiting an enantiopure configuration of ,-() and an achiral ,--isomer (). The X-ray structures of and reveal the presence of supramolecular arrangements driven by intermolecular H-bonding. A significant intermolecular closer proximity in than that in is depicted, ultimately resulting in a slow thermal (days) and swift (min) photochemical polymerization of to form , whereas is unreactive. DFT computations indicate that in both cases the lowest energy-excited state is the charge-transfer state [CT; PhC*MeNH(CO) → π*(-C≡C-C≡C-)]. Therefore, this outcome illustrates a drastic selectivity via a settle change in a carbon configuration. Analysis demonstrates that is nonemissive and that its coloration arises from a π → π* excitation of the polymer backbone (DFT computations).