Fluorescent and charge transport properties of columnar phases made of mono and bi-phenazine derivatives

Abstract

Mesogenic dibenzophenazine derivatives have been synthesized and their liquid crystalline, fluorescent and electrochemical properties have been studied. All compounds form the Col_hd phase, one of them (4-hydroxyphenyl 2,3,6,7-tetrakisoctyloxy-dibenzo[a,c]phenazine-11-carboxylate, 4) additionally shows an unusual columnar structure with p2mg symmetry, which is a partially lamellarized columnar phase. The emission spectra exhibit a huge Stokes shift that is due to the different molecular conformation in ground and excited states. The non-dispersive hole transport current under UV laser illumination was observed and the charge mobility in the range 10⁻⁴–10⁻³ cm² V⁻¹ s⁻¹ was determined with the time of flight (ToF) method. The measurements have been interpreted according to the Gaussian disorder model, providing material parameters that reflect the energetic distribution of localized states (diagonal disorder, σ) and distribution of coupling parameters between transport sites (off-diagonal disorder, Σ).