Thermochromic and highly tunable color emitting Bis-tolane based liquid crystal materials for temperature sensing devices

Abstract The luminescent compounds based on the D-π-A system consisting of substituted pyrrole as acceptor, π conjugated bis-tolane and -OMe, -N(CH3)2, -N(Ph)2 at termini acting as donors have been synthesized. On heating, all the compounds exhibited distinct mesomorphic behavior depending upon donating groups and substituents at the acceptor unit. These luminescent liquid crystals exhibited emission from blue, green to reddish orange with high quantum efficiency in solid as well in solutions state. We discovered the rarely reported three membered ring interactions between the Br at alpha position of pyrrole and acetylene bond and their impact on luminescence efficiency via single crystal structure of 2Br-CN-N(CH3)2 and 2Br-CN-N(Ph)2. Furthermore, the thermochromic behavior of these LLCs compounds has been explored, especially CN-N(Ph)2, its reddish orange emission changed to blue at 240 °C to 250 °C in pure state, while in dimethyl silicone polymer (PDMS) film, it switched to blue at 200 °C and completely vanished at 240 °C. These simple and highly emissive compounds display outstanding thermochromic properties above 200°C, thus will be potentiality valuable for high temperature sensing devices.