Multicolored Cathodically Coloring Electrochromism and Electrofluorochromism in Regioisomeric Star-Shaped Carbazole Dibenzofurans

Abstract

In this work, a series of fluorescent cathodically coloring electrochromic (EC) small molecules o-, m-, and p-DBFDCz with 3,5-di­(9H-carbazol-9-yl)­benzene (DCz) linked to dibenzofuran (DBF) at different substitutional positions were synthesized and fully characterized. These compounds are electroactive and undergo quasi-reversible two-step single-electron reduction generating radical anions and dianions. The absorptions of o-, m-, and p-DBFDCz in the neutral states lie in the UV region (λonset ≈ 350 nm), showing high transparency, while the absorption of their reduced states can be largely tuned across the visible region through driving voltage and substitutional positions. Initially generated spectroelectrochemically radical anions show absorption in the short-wavelength region of ∼380–500 nm with weak broad absorptions at longer wavelengths. On further reduction, these bands disappear on the cost of growing intense bands from dianions at longer wavelengths of 500–700 nm with some tail absorptions in the shorter-wavelength region. This renders the colors of the EC devices based on these materials, which are changed from green to red, yellow to magenta, and light to deep blue for o-, m-, and p-DBFDCz, respectively, covering four legs of the L*a*b* color space. Besides excellent optical contrast (>90%) and high coloration efficiency (up to 504 cm2 C–1), the fluorescence observed in solution of neutral o-, m-, and p-DBFDCz can be modulated between the fluorescence and quenched states by direct electrochemical redox reactions. Both EC and electrofluorochromic (EFC) processes are reversible on cycling. This research demonstrates the feasibility of developing multifunctional EC/EFC materials with multicolored electrochromism through exploiting electrochemical properties of traditional fluorescent small molecules.

Tuning the UV/Vis Absorption Spectra of Electrochromic Small Molecular Radicals Through Bridge Modulation

“…The electrochemical system comprised of a three‐electrode cell configuration with Pt‐screen as the working electrode, Ag wire as the pseudo‐reference electrode, and Pt‐wire as the counter electrode. The measurement settings adopted here are the same as reported in our previous work [16] . The reference electrode was calibrated versus the ferrocene/ferrocenium redox couple (Fc/Fc + ) ( E 1/2 Fc/Fc + =0.60 V vs .…”

“…It is worth noting that, due to the strong electron-affinity of 1,3,5-triazine, the reduction potentials of these materials are about 0.6 V lower than our previous work which employed a weak acceptor, dibenzofuran. [16] Another improvement in terms of molecular design is that the oxidative polymerization of materials is prevented on the counter electrode due to the carbazole being protected by phenyl groups at the 3-and 6positions, which largely enhances their electrochemical cycle stability. Meanwhile, the ECDs incorporating TACzs as the electrochromic functional materials are fabricated with a sandwich structure.…”

“…The measurement settings adopted here are the same as reported in our previous work. [16] The reference electrode was calibrated versus the ferrocene/ferrocenium redox couple (Fc/Fc + ) (E 1/2 Fc/Fc + = 0.60 V vs. Ag wire) (Figure S13b). The solution of 1.0 mM of TACzs in DMF with 0.1 M of nBu 4 NPF 6 was used in all spectro-electrochemical measurements.…”

Electrochemical Fluorescence Switch of Organic Fluorescent or Fluorogenic Molecules

“…The example of carbazole, a polycyclic aromatic hydrocarbon consisting of two six-membered benzene rings fused on either side of a five-membered nitrogen-containing ring is interesting. When combined with dibenzofuran, the original carbazoledibenzofuran derivatives display both EC and EFC properties [17]. From the EFC point of view, it was shown that the fluorescence intensity of these carbazole-dibenzofuran derivatives can be reversibly modulated from their redox states.…”

Preparation and electrochromic properties of polyamides based on 3,4‐dimethylthieno[2,3‐b]thiophene

“…Triphenylamine series organic electrochromic materials had become a research hotspot in the field of electrochromism because of the high coloring efficiency and polychromatic properties. Nevertheless, in comparison to other color types, electrochromism had many unique advantages, such as low energy consumption, low working voltage, many and high color states, good cycling durability and reversible, reasonable memory effect and so on 5,6 . Therefore, electrochromism had been applied in a variety of commercial applications, such as smart windows, biosensors, display devices, optical communications, glass mirrors and thermal control of spacecraft 1,7 …”