Polarized photoluminescence from nematic and chiral-nematic liquid crystalline films

Polarization control is key to optoelectronics in terms of the processing and display of optical information. In principle, photonic or electronic excitation of anisotropic films should result in polarized light emission. Because of spontaneous molecular self-assembly, liquid crystals are ideal for the exploration of polarized luminescence. Although most studies on polarized luminescence have been based on liquid crystalline fluid films, solid films are preferred in view of morphological stability.;Therefore, the theme of my thesis is the study of polarized luminescence from various fluorescent liquid crystal systems. From the fundamental perspective, a theory modeling the process of polarized photoluminescence was validated using fluorophore doped fluid liquid crystal films. To provide the morphological stability crucial to practical application, polarized fluorescence using vitrifiable and polymeric liquid crystals functionalized with fluorescent moieties was investigated. In addition, liquid crystalline pi-conjugated polymers were synthesized and characterized as a new class of optical polymers. The effect of the emission source on achievable polarization from pyrene and carbazole systems was also elucidated.;The main observations are as follows: (1) The observed degrees of polarization for all fluorescent liquid crystal systems were found to agree with the theories governing polarized fluorescence. (2) Low molar mass vitrifiable and polymeric liquid crystalline cyanoterphenyl and cyanotolane derivatives were found to yield moderate polarized fluorescence. Monomer emission was established as the decay pathway for the precursors and cyclohexane and polymethacrylate derivatives. (3) Ordered solid films from thiophene and p-phenylene pi-conjugated polymers were found to induce significant degrees of polarized fluorescence. (4) Emission from glass-forming pyrenyl derivatives exhibited excimer emission in dilute solution and neat film, whereas in solid hosts it was from monomers. Carbazolyl derivatives exhibited mostly monomer emission in all media. Polarized emission results indicate the ease of pyrenyl alignment presumably because of the favorable regiochemistry and conformational flexibility.