Charge-carrier Transport in Nematic 2-(p-Decyloxybenzylideneamino)-9-Fluorenone

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Abstract
2-(p-Decyloxybenzylideneamino)-9-nuorenone (DBAF), with a large π-electronic group, showed a transient photocurrent induced by the strongly-absorbed light from a N2 gas laser in the nematic, monotropic smectic, and isotropic liquid states. This photocurrent seemed to be due to the space-charge-limited current. The drift mobilities of the positive and negative charge carriers (μp and μn respectively) were determined from the peak time. The μn was ten times larger than μp, while the activation energies were identical. The modified Walden rule was valid in the nematic state ranging from 90 °C to 135 °C. The nematic mixtures of DBAF and N-(p-methoxybenzylidene)-p-butylaniline also showed a similar transient photocurrent, the magnitude of which increased significantly with an increase in the DBAF content. The mobilities were independent of the DBAF content and were nearly equal to those in nematic DBAF at the same viscosity, η: that is, μn=3×105, and μp=2.5×10−6 cm2/V s at η=0.026 Pa s. These facts indicate that the nature of the carrier transport of the photoconduction is not electronic, but ionic. The O2− and the cation radical of DBAF are proposed as the ionic carrier species for both nematic DBAF and the nematic mixtures.

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