Liquid Crystalline Oligofluorenes

Monodisperse glassy liquid crystalline conjugatedoligomer films are promising for application inoptics, photonics and electronics. This research hasfurnished fundamental understanding of the origin ofchiroptical effects in glassy-cholestericoligofluorene films and new insight into thephotoalignment of glassy-nematic oligofluorene films.Specifically, cholesteric films, which emerged uponthermal annealing of spin-cast films of chiraloligofluorenes, showed an order-of-magnitude increasein circular dichroism and a handedness reversal incircularly polarized fluorescence compared to theamorphous pristine films. The oligomer chain lengthplayed an important role in solid morphology. Theorientation of monodisperse glassy-nematicoligofluorenes was characterized on photoalignmentlayers comprising a polymethacrylate backbone withcoumarin pendants. A transition from a parallel to aperpendicular orientation with reference to thepolarization axis of UV-irradiation was observed at ahigh extent of coumarin dimerization. A kinetic modelwas used to interpret the photodimerization ofcoumarin and to evaluate the relative importance ofthe factors affecting the crossover behavior.

Autorentext

PhD and MS in Chemical Engineering, University of Rochester, Rochester, New York; MS in Materials/Polymer Science and BS Chemical Engineering, Sts Cyril and Methodius University, Skopje, Macedonia. Her research interests include multi-functional materials for optics and photonics, as well as novel methods for liquid crystal alignment.

Klappentext
Monodisperse glassy liquid crystalline conjugated oligomer films are promising for application in optics, photonics and electronics. This research has furnished fundamental understanding of the origin of chiroptical effects in glassy-cholesteric oligofluorene films and new insight into the photoalignment of glassy-nematic oligofluorene films. Specifically, cholesteric films, which emerged upon thermal annealing of spin-cast films of chiral oligofluorenes, showed an order-of-magnitude increase in circular dichroism and a handedness reversal in circularly polarized fluorescence compared to the amorphous pristine films. The oligomer chain length played an important role in solid morphology. The orientation of monodisperse glassy-nematic oligofluorenes was characterized on photoalignment layers comprising a polymethacrylate backbone with coumarin pendants. A transition from a parallel to a perpendicular orientation with reference to the polarization axis of UV-irradiation was observed at a high extent of coumarin dimerization. A kinetic model was used to interpret the photodimerization of coumarin and to evaluate the relative importance of the factors affecting the crossover behavior.