Reversible Charge Trapping in Bis-Carbazole-Diimide Redox Polymers with Complete Luminescence Quenching Enabling Nondestructive Read-Out by Resonance Raman Spectroscopy

Abstract

The coupling of substituted carbazole compounds through carbon–carbon bond formation upon one-electron oxidation is shown to be a highly versatile approach to the formation of redox polymer films. Although the polymerization of single carbazole units has been proposed earlier, we show that by tethering pairs of carbazoles double sequential dimerization allows for facile formation of redox polymer films with fine control over film thickness. We show that the design of the monomers and in particular the bridging units is key to polymer formation, with the diaminobenzene motif proving advantageous, in terms of the matching to the redox potentials of the monomer and polymer film and thereby avoiding limitations in film thickness (autoinsulation), but introduces unacceptable instability due to the intrinsic redox activity of this moiety. The use of a diimide protecting group both avoids complications due to p-diamino-benzene redox chemistry and provides for a redox polymer in which the photoluminescence of the bis-carbazole moiety can be switched reversibly (on/off) with redox control. The monomer design approach is versatile enabling facile incorporation of additional functional units, such as naphthalene. Here we show that a multicomponent carbazole/naphthalene containing monomer (APCNDI) can form redox polymer films showing both p- and n- conductivity under ambient conditions and allows access to five distinct redox states, and a complex electrochromic response covering the whole of the UV/vis–NIR spectral region. The highly effective quenching of the photoluminescence of both components in poly-APCNDI enables detailed characterization of the redox polymer films. The poly-APCNDI films show extensive charge trapping, which can be read out spectroscopically in the case of films and is characterized as kinetic rather than chemical in origin on the basis of UV/vis–NIR absorption and resonance Raman spectroscopic analyses. The strong resonantly enhanced Raman scattering for the various oxidized and reduced states of APCNDI enables nondestructive “read-out” of the state of the polymer, including that in which charges are trapped kinetically at the surface, making poly-APCNDI highly suitable for application as a component in organic nonvolatile memory devices.

Proton-Stabilized Photochemically Reversible E/Z Isomerization of Spiropyrans

“…are highly desirable due to the possibility to tune these physical responses through structural (synthetic) modification. 10 Building such molecular switches into materials can impart responsiveness at the macroscopic level, often amplifying the changes in physical properties ranging from sensing 11 and surface properties 12 to luminescence 13 , 14 and electrochromism. 15 , 16 Photochromes, including dithienylethenes, 17 , 18 azobenzenes, 19 , 20 and spiropyrans, 21 are among the most widely applied, due to their modularity and flexibility toward modification and the possibility to combine them with other responsive units, e.g., multiphotochromes.…”

Electrochemical Polymerization Provides a Function‐Integrated System for Water Oxidation

“…In the first cycle (Figure 1 a), the oxidation peak was observed at approximately 0.278 V (vs. Fc/Fc + ), and the peak was assigned to the oxidation of the cobalt center, Co III 3 Co IV /Co III 4 [13] . Upon further sweeping of the potential to the positive region, a large peak attributed to the oxidation of the carbazole moieties was observed at approximately 0.7 V. In the reverse scan, two new redox waves were observed at 0.323 and 0.601 V. These redox waves were due to the formation of a biscarbazole structure [10] . In the second and subsequent cycles (Figure 1 b), the intensity of the current attributed to the redox couple of biscarbazole ( E 1/2 =0.432 and 0.755 V) was increased, indicating the formation of further biscarbazole moieties upon electrochemical oxidation.…”

Electrochemical Polymerization Provides a Function‐Integrated System for Water Oxidation

“…Carbazole derivatives are known to dimerize under oxidative conditions (Scheme 2 a). [9] In addition, the formed biscarbazole exhibits hole‐transfer ability (Scheme 2 b), [10] which should favor the oxidative catalytic reaction. Therefore, materials with catalytic centers and hole transporters should be accessible ( Poly‐1 , Scheme 1, bottom) by the electrochemical polymerization of 1 .…”