Photophysical and photoconductive properties of a carbazolyl derivative with a mesogen group of alkoxycyanobiphenyl in mesophases
4-Cyano-4′-(1-(N-carbazolyl)-n-octyloxy)biphenyl (8OCBCz), where the hydrogen atom of a well-known mesogen 4-cyano-4′-n-octyloxybiphenyl (8OCB) is substituted with one carbazolyl (Cz) chromophore, was synthesized, and the photophysical and photoconductive properties of its neat form and its binary mixtures with 4-cyano-4′-n-decyloxybiphenyl (10OCB) were investigated. The 8OCBCz exhibited intermolecular exciplex fluorescence in concentrated solutions. When 8OCBCz was quenched from its molten state, it formed an amorphous state, which exhibited exciplex fluorescence and transient photocurrent signals of both the positive and negative charge carriers. However, their mobilities could not be determined because of the strongly dispersive signals. The mixtures exhibited smectic A (Sm A) and nematic (N) mesophases. These mesophases and the isotropic phase exhibited exciplex as well as monomer fluorescence. The exciplex formation mechanism in the Sm A mesophase differed from those in the N and isotropic phases. The transient photocurrent signals for both the positive and negative charge carriers were also observed for the binary mixtures. Ionic conduction was suggested for the N and isotropic phases, whereas electronic conduction was suggested for the Sm A mesophase. The ionic carrier species were proposed.
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 189, Issue 1, 10 June 2007, Pages 55–64