Control Over Topochemical Photopolymerization and Photoisomerization in Azobenzene Tethered Chiral Diacetylenes Toward Tunable Molecular Packing and Conductivity

Abstract

Polydiacetylenes (PDAs) play a pivotal role in sensing and recognition owing to their stimuli-responsive optoelectronic properties. Inducing chirality in polydiacetylenes provides an additional handle for generating tunable chiroptical behavior in materials toward chiral optoelectronics and photonics. A photopolymerizable diacetylene (DA) tethered with chiral (R/S) phenylalanine and an azobenzene photoswitch (1_R/S-DA) is designed, with a suitable control molecule 2_DA devoid of the chiral motif. The designed molecules self-assemble in aqueous and organic solvent systems. The chiral PDAs show better packing efficiency in monolayers and record higher photoisomerization percentages as compared to the achiral analog. Further, higher photoisomerization percentages are observed in the organic solvent system. In both chiral (1_S-PDA) and achiral (2_PDA) polymers, E-Z photoisomerization leads to the weakening of the self-assembly. Microscopic and X-ray scattering investigation suggest excellent birefringence in E-1°_S-PDA owing to better molecular ordering in comparison to Z-1°_S-PDA and E-1^a_S-PDA. Better molecular ordering of the conjugated polymer in organic solvent (E-1°_S-PDA) renders a higher charge storage propensity as compared to the aqueous solvent. Finally, photo-controlled E-Z isomerization in the azobenzene motifs embedded within polymer domains exhibits modulation in conductivity with E-1°_S-PDA having ≈3-fold superior conductivity than Z-1°_S-PDA in solution-processed thin films.