Polarized Photoluminescence of a Liquid Crystalline Monosubstituted Polyacetylene upon Photoexcitation with an Ultraviolet Laser

Despite the general belief that monosubstituted polyacetylenes are unpromising candidates for luminescent materials, we synthesized a highly luminescent poly(1-alkyne) with liquid crystalline pendants. Upon excitation by an ultraviolet laser line of 325 nm, strong deep-blue photoluminescence (PL) at ~400 nm was detected in its dilute solutions. The calculated band structures indicate that the blue PL originates from the mesogenic pendants. In a more concentrated solution (1.13*10-2 M), the blue PL exhibits electrically controllable angular dependence. Dramatic changes both in spectral shape and in emission intensity were observed at and above a threshold field of 3.2*10^5 V/m. Our results reveal that the molecular alignment induced by the polarized ultraviolet laser plays a key role in its polarized PL emission.