Charge Transport in the Mesomorphic Free-Radical Compound Bis(octakis(dodecyloxy)phthalocyaninato)lutetium(III)

We have used the pulse-radiolysis time-resolved microwave conductivity technique (PR-TRMC) to study the charge transport properties of the free-radical sandwich complex bis(octakis(dodecyloxy)phthalocyaninato)lutetium(III), [(C 12 O) 8 Pc] 2 Lu. This compound displays multimesomorphic thermotropic behavior with two columnar liquid crystalline phases, D x and D h, between the freshly precipitated crystalline solid at room temperature, K v, and the isotropic liquid, I, at 196 °C. In contrast with all other discotic materials previously studied using the PR-TRMC technique, the mobility of charge carriers is found to increase markedly at the transition from the K v phase to the first columnar mesophase, D x . The mobility displays a further substantial increase on entering the higher temperature hexagonal columnar phase, D h . The intracolumnar mobility determined just above the D x → D h transition temperature of 90 °C is 0.17 × 10 -4 m 2 /(V s), which is the highest yet determined for a columnar liquid crystalline material. The decay kinetics of the mobile charge carriers show a complex dependence on temperature with a first half-life that increases by orders of magnitude at the K → D x and D x → D h transitions. The results are discussed in terms of both intramolecular and intermolecular structural changes.