Selective Chirality-Driven Photopolymerization of Diacetylene Crystals.

Crystal engineering of two diacetylene monomers was achieved by branching two chiral groups [R = PhC*MeNH(CO 2 )CH 2 ] exhibiting an enantiopure configuration of S , S -( DA2 ) and an achiral R , S - meso -isomer ( DA4 ). The X-ray structures of DA2 and DA4 reveal the presence of supramolecular arrangements driven by intermolecular H-bonding. A significant intermolecular closer proximity in DA4 than that in DA2 is depicted, ultimately resulting in a slow thermal (days) and swift (min) photochemical polymerization of DA4 to form PDA5 , whereas DA2 is unreactive. DFT computations indicate that in both cases the lowest energy-excited state is the charge-transfer state [CT; PhC*MeNH(CO 2 ) → π*(-C≡C-C≡C-)]. Therefore, this outcome illustrates a drastic selectivity via a settle change in a carbon configuration. Analysis demonstrates that PDA5 is nonemissive and that its coloration arises from a π → π* excitation of the polymer backbone (DFT computations).