An Electrochromic Nanostructured Liquid Crystal Consisting of π-Conjugated and Ionic Moieties

Abstract

A new electrochromic molecule comprised of pi-conjugated and ionic moieties has been designed and synthesized. It forms a nanosegregated smectic phase in which ion-conductive layers of imidazolium salts are located between hole transport layers of phenylterthiophene moieties. Electrochromism is observed in the bulk liquid crystal state of this compound without an electrolyte solution. In this nanosegregated smectic phase, an electrical double layer is formed rapidly at the electrode. Consequently holes are injected from the electrode, resulting in oxidation of the pi-conjugated moieties.

Electrofluorochromism in π-conjugated ionic liquid crystals

“…Here an electrochromic response in the bulk LC phases is observed in electron acceptor p-conjugated ionic liquid crystals (ILCs), while a similar behaviour has been reported only by Kato and colleagues for hole-conducting ILCs self-segregating in SmA phases 26,27 .…”

“…As previously suggested by Kato and colleagues, electrochromism in p-conjugated ILCs is possible because of the coupling of electronic and ionic functions in the nanosegregated structure of ILCs 26,27 . Electron injection at the cathode causes the reduction of the thienoviologen dication and the reduced species is transferred to the anode by electron hopping via p-p intermolecular interaction through the film.…”

“…Supplementary Figure 3 displays a representative impedance spectrum of 1 at 120°C where a high frequency relaxation process ( relaxation frequency B400 Hz) and an incomplete low frequency one can be seen. The first process is attributed to the bulk resistance of the material (R b ) while the latter is associated with the charge transfer resistance of the interface between sample and electrode [26][27][28][29] . Ionic conductivity (s) was calculated using the equation (1):…”

“…where K cell is the cell constant given by the ratio between cell gap and electrode area [26][27][28][29] . R b was obtained from the semicircle diameter on the real axis (Z 0 ) ( Supplementary Fig.…”

Integration of electro-active π-conjugated units in nanosegregated liquid-crystalline phases

“…Phenylterthiophene derivatives bearing an imidazolium unit exhibit nanosegregated smectic phases in which hole-transporting redox-active layers and ion-conductive layers are integrated separately. 25,26 As shown in Figure 1, the DC bias application induces the formation of an electrical double layer that promotes hole injection from the anode to the redox active layers. This coupling of the electronic function of the π-conjugated units with the ionic conductivity causes anodic oxidation, resulting in electrochromism without an electrolyte solution.…”