Time-of-flight study of electrical charge mobilities in liquid-crystalline zinc octakis(β-octoxyethyl) porphyrin films

Abstract

Time-of-flight measurements performed on micron-thick films of liquid-crystalline zinc octakis(β-octoxyethyl) porphyrin indicated that charge carriers possess significantly high drift mobilities, attaining approximately 0.01 cm2 V−1s −1 and 0.008 cm2 V−1s −1 for holes and electrons, respectively, at room temperature. Upon heating the samples from 300 to 420 K, causing the porphyrin to go from the solid-crystalline to the discotic mesophase, the mobilities did not decrease drastically, and remained at values slightly larger than half those observed at room temperature. Charge transport in this material conformed to the Scher–Montroll model, which attributes a distribution of hopping times to the propagation of the initially formed charged carrier packet. Analysis of the “universal” plots prescribed by this model yielded a dispersion factor of 0.5 for both charge carriers.

Aging continuous time random walks

“…What is clear is that on a phenomenological level, one can use the Scher-Montroll approach to fit behaviors of charge currents in a large number of experiments in very different systems. For example, transport of charge carriers in: organic photo-refractive glasses [57], nano-crystalline T i O 2 electrodes [58], conjugated polymer system poly pphenylene [59,60], and liquid crystalline xinc octakis [61]. Scher and Montroll model such transport processes using non-equilibrium biased CTRW theory with an effective waiting time distribution.…”

“…At this time it is still an open question if ACTRWs can be used to describe aging in real systems. Further it is not clear if aging in the above mentioned systems [57,58,59,60,61] is measurable, and if so do these very different systems exhibit any common aging effects in their transport?…”

Synthesis and characterization of a new unsymmetrical porphyrin liquid crystal and its lanthanide complexes

“…There has been increasing interest in designing and synthesizing discotic liquid crystals due to their potential application in fields like charge-transfer processes [7], photoconductivity [8], thermal switching [9] and organic electroluminescence [10]. Most discotic liquid crystals have a molecular structure that consists of a flat central core with several alkyl chains placed around the outside edge of the core [11].…”

Hole mobility and lifetime in a smectic liquid crystalline photoconductor of a 2-phenylnaphthalene derivative

“…Since high hole mobilities over 10 −3 cm 2 / V s in a triphenylene derivative of discotic liquid crystals 1 and a 2-phenylbenzothiazole derivative of smectic liquid crystals 2 were discovered in 1990s, they have been reported in many different types of liquid crystals including perylenes, 3 porphilines, 4 benzocoronens, 5 2-phenylnaphthalenes, 6 benzothienobenzothiophenes, 7 and terthiphenes 8 and even in polymeric liquid crystals such as polyfluorenes. 9 Thus, liquid crystals have become recognized as a new type of quality organic semiconductor exhibiting self-organization.…”