Prominent Electron Transport Property Observed for Triply Fused Metalloporphyrin Dimer: Directed Columnar Liquid Crystalline Assembly by Amphiphilic Molecular Design

摘要

Organic semiconductors have attracted increasing attention in view of their potential for low-cost alternatives to amorphous silicon and design flexibility for elaborate electronic devices. In particular, liquid crystalline (LC) semiconductors composed of large π-con-jugated molecules are attractive in that their columnar assembly could provide an anisotropic electrical pathway for charge carriers. Moreover, LC materials are solution-processable into large-area thin devices. Representative examples include LC assemblies of large jr-conjugated molecules such as triphenylenes, hexabenzocoro-nenes, perylene diimides, porphyrins, and phthalocyanines, where a molecule with a larger π-conjugated core tends to show a higher charge-carrier mobility. Here we report the first LC material of a fused metalloporphyrin dimer (1_(C12/TEG); Chart 1) that displays a top-class intrinsic electron trasport property among those reported for n-type LC semiconductors. Triply fused metalloporphyrin dimers are a new class of extra-large π-conjugated molecules and potentially interesting for organic electronics. However, the reported crystal packing diagrams mostly adopt a T-shaped molecular geometry, which is unfavorable for electrical conduction. According to a common strategy for liquid crystallization, we initially incorporated paraffinic (C_(12)) side chains into the periphery of a triply fused copper porphyrin dimer (1_(C12/C12); Chart 1). However, this strategy failed to give any ordered structures. We then prepared compound 1_(TEG/TEG) having hydrophilic triethylene glycol (TEG) chains and, just for curiosity, amphiphilic 1_(C12/TEG). Quite interestingly, only 1_(C12/TEG) formed a room-temperature columnar liquid crystal.