ABSTRACT
Property optimization through orientation control of metal-organic framework (MOF) crystals that exhibit anisotropic crystal structures continues to garner tremendous interest. Herein, an electric field is utilized to post-synthetically control the orientation of conductive layered Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) crystals dispersed in an electronically insulating poly(ethylene glycol) diacrylate (PEGDA) oligomer matrix. Optical and electrical measurements are performed to investigate the impact of the electric field on the alignment of Cu3(HHTP)2 crystals and the formation of aggregated microstructures, which leads to an ≈5000-fold increase in the conductivity of the composite. Notably, the composite thin-films containing aligned Cu3(HHTP)2 crystals exhibit significant conductivity of ≈10-3 S cm-1 despite the low concentration (≈1 wt.%) of conductive Cu3(HHTP)2. The use of an electric field to align Cu3(HHTP)2 crystals can rapidly generate various desired patterns that exhibit on-demand tunable collective charge transport anisotropy. The findings provide valuable insights toward the manipulation and utilization of conductive MOFs with anisotropic crystal structures for various applications such as adhesive electrical interconnects and microelectronics.
ABSTRACT
Developing inorganic-organic composite polymers necessitates a new strategy for effectively controlling shape and optical properties while accommodating guest materials, as conventional polymers primarily act as carriers that transport inorganic substances. Here, a universal approach is introduced utilizing mesoporous liquid crystal polymer particles (MLPs) to fabricate inorganic-organic composites. By leveraging the liquid crystal phase, morphology and optical properties are precisely controlled through the molecular-level arrangement of the host, here monomers. The controlled host material allows the synthesis of inorganic particles within the matrix or accommodation of presynthesized nano-inorganic particles, all while preserving the intrinsic properties of the host material. This composite material surpasses the functional capabilities of the polymer alone by sequentially integrating one or more inorganic materials, allowing for the incorporation of multiple functionalities within a single polymer particle. Furthermore, this approach effectively mitigates the drawbacks associated with guest materials resulting in a substantial enhancement of composite performance. The presented approach is anticipated to hold immense potential for various applications in optoelectronics, catalysis, and biosensing, addressing the evolving demands of the society.
ABSTRACT
Metal-organic frameworks (MOFs) represent crystalline materials constructed from combinations of metal and organic units to often yield anisotropic porous structures and physical properties. Postsynthetic methods to align the MOF crystals in bulk remain scarce yet tremendously important to fully utilize their structure-driven intrinsic properties. Herein, we present an unprecedented composite of liquid crystals (LCs) and MOFs and demonstrate the use of nematic LCs to dynamically control the orientation of MOF crystals with exceptional order parameters (as high as 0.965). Unique patterns formed through a facile multidirectional alignment of MOF crystals exhibit polarized fluorescence with the fluorescence intensity of a pattern dependent on the angle of a polarizer, offering potential use in various optical applications such as an optical security label. Further, the alignment mechanism indicates that the method is applicable to numerous combinations of MOFs and LCs, which include UV polymerizable LC monomers used to fabricate free-standing composite films.
