Siloxane tethered perylene diimide: from monotropic phase structures to tunable photoconductivity

Abstract

A novel perylene diimide derivative bearing siloxane moieties (PDI-TTMSS) was synthesized by a simple one-step reaction. By the combination of spectroscopic, microscopic and scattering experiments, we have demonstrated that PDI-TTMSS exhibits peculiar monotropic phase transition behaviors originated from the flexible siloxane substituents. The PDI-TTMSS sample cooled from isotropic melt possesses a nematic columnar structure (Φ_N) with good processability, but its charge-carrier mobility is too low to be detected due to the lack of close π stacks. After annealing above the temperature of cold crystallization, the liquid crystalline structure Φ_N can transform to an ordered crystalline structure (Φ_K) with close π–π stacking of the PDI cores, endowing PDI-TTMSS with enhanced charge-carrier mobility. It is hoped that our results concerning the structure–property relationship can evoke some investigations on controlling the photoelectric properties of conjugated materials by different processing sequences or simple thermal treatments.