(161ao) Exploring the Synthesis-Structure-Property of Dye Incorporated Liquid Crystalline Polymers within Unique Polymeric Templates

Stimuli-responsive dyes are in great demand due to their tunable optical properties upon application of mechanical force/pressure, heat or UV light. Among these, mechanochromic dyes possess color changing properties as a result of applied force and can be very useful for mechanical damage sensing, pressure sensors, crack detection and testing mechanical system failure applications. Coupling these dyes with structural photonic polymers can create a new platform of tunable optical hybrid materials. Cholesteric liquid crystalline polymers are known to be thermally responsive where their optical properties can be tuned with temperature. To further expand the functional capabilities of cholesteric polymers, we have synthesized mechanochromic dye incorporated cholesteric liquid crystalline polymers to achieve both mechanochromic and thermochromic response. Molecular engineering of mechanochromic monomers is the key to couple mechanochromic and thermochromic response. Synthesis-structure-property investigation of the dye incorporated liquid crystalline polymers reveals the importance of (1) alkyl spacer length used to tether the dye to the monomer and (2) number and points of attachment of polymerizable unit onto the dye. Two-sided attachment of the polymerizable group to the mechanochromic dye moiety (bifunctional monomers) result in crosslinked polymer network structures that are responsible for the mechanochromic behavior. The precise tailoring of the mechanochromic dye monomer within the liquid crystalline polymer framework allows the unique synergistic and cooperative interactions between liquid crystalline cholesteric phase (N* phase) and mechanochromic dye molecules. Thus, a multi-functional elastomeric system with tunable optical emission as a result of both mechanochromic and thermochromic response can be envisioned for mirrorless lasing, actuators, thermal sensors and photonic applications.