Liquid Crystalline Metal-free Phthalocyanines Designed for Charge and Exciton Transport

Abstract

A joint theoretical and experimental study of the electronic and structural properties of liquid crystalline\nmetal-free phthalocyanines bearing a strong potential for charge and exciton transport has been performed.\nThe synthesis of such compounds has been triggered by quantum chemical calculations showing that: (i)\nhole transport is favored in metal-free phthalocyanines by their extremely low reorganization energy (0.045\neV) and large electronic splittings; and (ii) the efficiency of energy transfer along the one-dimensional discotic\nstacks is weakly affected by rotational disorder due to the two-dimensional character of the molecules. We\nhave synthesized two metal-free phthalocyanines with different branched aliphatic chains on the gram scale\nto allow for a full characterization of their solid-state properties. The two compounds self-organize in liquid\ncrystalline mesophases, as evidenced by optical microscopy, differential scanning calorimetry, X-ray powder\ndiffraction, and molecular dynamics simulations. They exhibit a columnar rectangular mesophase at room\ntemperature and a columnar hexagonal mesophase at elevated temperature.