Electro‐oxidative Polymerization and Spectroscopic Characterization of Novel Amide Polymers Using Diphenylamine Coupling

Abstract

We have electropolymerized 1,1 from CH3CN, tetrahydrofuran (THF), and CH5CI5 to form an alternating main chain polymer of diphenylbenzidine and ferrocene. As a comparison, we have electropolymerized 1,4 which lacks the electrochemical response of the ferrocene group. In nonaqueous solvents, the diphenylbenzidine group shows two reversible 1e oxidations. The second 1e oxidation of the diphenylbenzidine overlaps with the 1e oxidation of the ferrocene group at 0.88 V vs. Ag/AgCl in CH,C12. The electrochemistry of the polymer film in aqueous acid shows two 1e waves consistent with oxidation of the diphenylbenzidine group to the cation and then the dication. The spectroelectrochemsitry of both polymer films show broad, lowenergy, near-IR bands in aprotic solvents such as CH5C12, THF, and CH3CN and aqueous solutions with pH < 3. We assign these bands to intermolecular it stacking of the protonated diphenylbenzidinium cations. The electrochemistry of both materials is chemically reversible and forms the basis for electrochromic and redox applications.Ferrocene has many interesting properties related to its chemical and electrochemical reversibility, unusual protonation, and electrophilic substitution. Polymers in which ferrocene units are either in the main chain or in the side chains have been synthesized and studied extensively.1 The reversibility of this redox couple makes these systems ideal for chemically based device applications where long-term stability is important. Ferrocene-polymer-based modified electrodes have been extensively studied.2'3 Peerce and Bard reported that poly(vinylferrocene)-coated platinum electrodes can be used as a reference electrode in acetonitrile.4 This has been proposed as a standard reference electrode for nonaqueous electrochemical systems. Hickman et al.5 used a ferrocene-based polymer as an internal reference on a microelectrode array and showed that a voltammetric microsensor can have the reference and the sensor fimctions on the same "chip." Electrodes modified with ferrocene-based compounds have been suggested for biosensor applications.5 The ferrocene-modified enzyme electrode can determine the glucose concentration with ferrocene mediating the electron transfer.7' Ferrocene polymers have been used in the photoelectrochemical reduction of halocarbons and in solar applications." Self-assembled monolayers with ferrocene termini have helped elucidate the nature of charge transfer at interfaces.'2'4 Ferrocenebased charge-transfer complexes have been reported for applications requiring only moderate conductivity15 Conjugated conducting polymers based on ferrocene have been reported.'6'17 Ferrocene has been used as one component of ferromagnetic organic materials and as a group in secondorder, nonlinear optical materials. '8'19 Recently, our group has been interested in studying polymers with the structural motif of (-R-X-R-),,, where R is the polymerizable end group.2' X can be electroactive and can have a different set of redox and optical properties than R. The monomers are eas...

Coronene Diimide Containing Redox Active Electrochromic Polymer Film via Electropolymerization of Diphenylamine End Groups

“…The oxidative redox couples correspond to the presence of electroactive DPB in the polymer chain producing two radical cations, DPB + and DPB 2+ consistent with previous work done in our group. [7][8][9][10][11][12][13] Also linear dependence the peak current dependence on the scan rate confirmed that the polymer film was surface confined ( Figure 3). The electrochemical behavior of DPB group in non-halogenated solvents is different.…”

“…Our research group has focused on synthesizing new monomers containing a central redox active moiety flanked by two electropolymerizable functional groups and subsequently, studying the mechanism of this process as well as their optical and electronic properties. [7][8][9][10][11][12][13] Perylene diimides have been reported as electron-transport materials with high electron mobility as well as having good chemical, thermal and photochemical stability. [14][15][16][17][18][19][20] Coronene derivatives have shown columnar discotic liquid-crystalline (LC) mesophases making them important candidates for organic electron transport materials due to extensive molecular ordering.…”

“…Similar results have been reported in case of electropolymerization of monomers containing naphthalene diimide, ferrocene, and perylene diimides. [7][8][9][10][11][12][13] As the first reverse scan (negative direction) of DCTD exhibits no reduction peak corresponding to 1.05 V oxidation peaks, the two new reduction peak were assigned for the reduction of newly formed diphenylbenzidine (DPB) cations (one for DPB + and the other for DPB 2+ ). The proposed polymer structure is shown in Scheme 2, based on previous work on numerous perylene, naphthalene and benzene diimide diphenylamine polymers.…”

“…Upon further oxidation, an intense absorption band appeared at 602 nm indicating oxidation to DPB 2+ with concommitant decrease in the intensity of the 900 nm band, indicating that the dication formation in the polymer chain reduces the π-stacking interaction. [7][8][9][10]12,13 Upon reduction of the polymer films at −1.0 V vs Ag/AgCl, a radical anion is formed with new absorption bands at 620 and 982 nm. Also the absorption bands between 400 to 513 nm dramatically decrease in intensity.…”

“…Upon further oxidation, the color changes to blue which is consistent with the previous results. 7,9,12 A cathodic change in potential results in a color change from yellow to violet to green, i.e. the two reduced states of polymer showed two different colors.…”