Redox-Responsive Chiral Dopant for Quick Electrochemical Color Modulation of Cholesteric Liquid Crystal

Abstract

Here, we report the first redox-active chiral dopant D, which electrically alters its helical twisting power (HTP) for a cholesteric liquid crystalline (LC) medium and quickly changes the reflection color.D is composed of an axially chiral binaphthyl unit in conjunction with a redox-active ferrocene unit. A cholesteric LC phase of 4'-pentyloxy-4-cyanobiphenyl, doped with D (3.0 mol %), developed a blue reflection color. When nitrosyl tetrafluoroborate, a one-electron oxidant, was added to this cholesteric LC phase,D was oxidized to decrease its original HTP value by 13%, so that a green reflection color was developed. In the presence of a supporting electrolyte, the reflection color was electrochemically modulated using a sandwich-type glass cell with indium tin oxide electrodes. In quick response to the applied voltage of +1.5 V, the reflection color changed from blue to green within 0.4 s. When 0 V was applied, the reflection color returned to its original blue color. The D-doped cholesteric LC is characterized by its fastest electrochemical response and lowest operating voltage among those reported for electrically driven cholesteric LC devices.

Electrothermal Color Tuning of Cholesteric Liquid Crystals Using Interdigitated Electrode Patterns

“…Besides the above-mentioned electrically responsive LC systems, an electric field can also act as an indirect stimulus, generating a second stimulus that distorts the pitch length. Some of the latest progress on color-tunable devices has been demonstrated by using an electrochemical, [25,26] electromechanical [27,28] or electrothermal [29][30][31] response in combination with (transparent) conductive substrates.…”

Recent Advances on Stimuli‐Responsive Smart Materials and their Applications

“…The addition of 3.0 mol% Fc D results blue reflection colour observed however addition of nitrosyltetrafluoroborate (NOBF 4 ) leads colour change to green colour and decrease in HTP from 116 μm −1 to 101 μm −1 . Subsequently, electrochemical properties performed highlighted the changes in reflection colours from blue to green at 1.5 V and attain the initial state at 0 V in 0.4 and 2.7 s. Thus, the design of novel redox‐active chiral dopant permit fast electrochemical response in cholesteric LC devices at low voltage find applications in electrochromic display devices (Figure ) …”

“…Subsequently, electrochemical properties performed highlighted the changes in reflection 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 colours from blue to green at 1.5 V and attain the initial state at 0 V in 0.4 and 2.7 s. Thus, the design of novel redox-active chiral dopant permit fast electrochemical response in cholesteric LC devices at low voltage find applications in electrochromic display devices ( Figure 8). [47] Recently, our group studied the effect of voltage on free base and metallated porphyrin appended ferrocene units (H 2 TTP-Fc and ZnTTP-Fc). The bulk electrolysis performed at constant potential of 1.4 V on both derivatives result enhanced current and charge generation of 37 mC and 4.5 μA exclusively for ZnTTP-Fc compared to H 2 TTP-Fc.…”

“…Molecular structures of voltage responsive systems. References[43][44][45][46][47][48][49][50][51][52][53][54][55][56][57].…”

A Comparative Study of the Semiconductor Behavior of Organic Thin Films: TCNQ-Doped Cobalt Phthalocyanine and Cobalt Octaethylporphyrin

“…Thus, it is particularly important to select an appropriate stimulus, when inducing alteration in terms of molecular conformations, symmetry, optoelectronic properties and crystalline phase transitions [15][16][17][18][19]. In this context, voltage is one of the most significant stimuli, as this influences electronic properties instantaneously and enhances generation of the current in device technology [20][21][22][23]. Another feature that alters electronic properties is the electron-donating or electron-accepting function performed by the Pc and the porphyrin, which form active layers inside optoelectronic devices.…”