Photo‐controlled alignment and helical organization in main‐chain liquid crystalline alternating polymers

Abstract

Materials with highly ordered nanoscale structures can translate molecular processes to macroscopic function. Here we report on the photo‐controlled organization of achiral alternating copolymers composed of discrete length blocks showing well‐defined sub‐10 nm morphologies. These alternating copolymers consist of main‐chain azobenzene building blocks alternating with discrete oDMS blocks of various precise lengths. Remarkably, we demonstrate the imprinting of a stable helical molecular arrangement in spin‐casted thin films by irradiation with circularly polarized light, without chiral dopant or plasticizer required. By following the out‐of‐equilibrium photo‐switching process over irradiation time, the mechanism of molecular reorganization is unraveled and rationalized with the nature of the morphology. Linear photo‐organization is preferentially reached with flexible and symmetric cylindrical structures while helical photo‐organization is most easily obtained with robust but rotatable lamella structures. These findings suggest that precision in the synthesis and assembly of alternating copolymers can lead to complete control over molecular organization and main‐chain motion.

Photo‐Imprinting of the Helical Organization in Liquid‐Crystal Networks Using Achiral Monomers and Circularly Polarized Light

“…The LD and CD signals were maintained even after heating to 200 °C, indicating the strong propensity of the LCNs obtained to maintain the order imprinted by light (Figure 3a, b). The g abs of CPL‐irradiated RM‐AzoSi 3 films was too small to find clear features in grazing‐incidence small‐angle scattering, but based on previous work, [7, 25] the helix axis orients perpendicular to the surface.…”

“…They assemble into well‐defined phase‐segregated structures with sub‐10 nm feature sizes. The role of discrete siloxanes provides both the well‐defined ordering of the photoswitches by phase separation and the flexibility of the polymer chains to improve segmental mobility [24, 25] . Hence, we envision that nano‐segregated mesogens combining azobenzenes and discrete oDMS will allow the alliance of nanoscale properties and flexibility in LC materials [26–29] and could offer a strategy to prepare cholesteric LCN by CPL irradiation.…”

Photo‐Imprinting of the Helical Organization in Liquid‐Crystal Networks Using Achiral Monomers and Circularly Polarized Light

“…The LD and CD signals were maintained even after heating to 200 °C, indicating the strong propensity of the LCNs obtained to maintain the order imprinted by light (Figure 3 a, b). The g abs of CPL‐irradiated RM‐AzoSi 3 films was too small to find clear features in grazing‐incidence small‐angle scattering, but based on previous work,[ 7 , 25 ] the helix axis orients perpendicular to the surface.…”

“…The role of discrete siloxanes provides both the well‐defined ordering of the photoswitches by phase separation and the flexibility of the polymer chains to improve segmental mobility. [ 24 , 25 ] Hence, we envision that nano‐segregated mesogens combining azobenzenes and discrete oDMS will allow the alliance of nanoscale properties and flexibility in LC materials[ 26 , 27 , 28 , 29 ] and could offer a strategy to prepare cholesteric LCN by CPL irradiation.…”

Charge transport in liquid crystal network of terthiophene-siloxane block molecules

“…Early examples are phasesegregated LCs, 16,17 while more recent examples are based on discrete length block co-oligomers with one block consisting of discrete oligodimethylsiloxane (oDMS). [18][19][20][21][22][23] These materials assemble into well-defined phase-segregated structures with sub-10 nm feature sizes. The discrete nature of both the siloxanes and the complementary block promotes phase separation.…”