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Spectroelectrochemical Approaches to Mechanistic Aspects of Charge Transport in meso-Nickel(II) Schiff Base Electrochromic Polymer
journal contribution
posted on 2017-07-12, 00:00 authored by Kamila Łępicka, Piotr Pieta, Aleksander Shkurenko, Paweł Borowicz, Marta Majewska, Marco Rosenkranz, Stanislav Avdoshenko, Alexey A. Popov, Wlodzimierz KutnerA new
redox conducting polymer, viz. poly[meso-N,N′-bis(salicylidene)-2,3-butanediaminonickel(II)],
poly[meso-Ni(II)-SaldMe], belonging to the Schiff base polymer family,
was electrochemically synthesized. The charge transfer and polymerization
mechanism were unraveled by simultaneous cyclic voltammetry (CV) and
in situ UV–vis, FTIR-ATR, and ex situ low-temperature ESR spectroscopy.
With the latter, a short-living paramagnetic transient form of electro-oxidized
poly[meso-Ni(II)-SaldMe] was detected. This form was identified as
the bisphenolic radical cation. In situ UV–vis and FTIR-ATR
spectroelectrochemistry measurements revealed that the charge transfer
of the polymer involved bisphenolic radical cation formation at the
potential lower than 0.80 V vs Ag/Ag+ and then dication
formation at the potential exceeding 0.80 V. The proposed mechanism
of electropolymerization of meso-N,N′-bis(salicylidene)-2,3-butanediaminonickel(II), meso-Ni(II)-SaldMe,
involves two steps. First, electro-oxidation of the monomer results
in bisphenolic radical cation generation, and then mutual binding
of these radicals at the para positions of aromatic
rings is activated by electron-donating phenol moieties. In this electropolymerization,
the Ni(II) metal center played the role of a template providing planarity
to the monomer molecule. Structures responsible for the charge transfer
in the polymer and formed during electropolymerization were modeled
with quantum chemistry calculations using the DFT method at the PBE
level. The resulting polymer film was highly conducting and stable
with respect to potential multicycling under cyclic voltammetry conditions,
from 0 to 1.3 V vs Ag/Ag+. Under these conditions, it changes
color from yellow through orange to russet for its neutral, bisphenolic
radical cation, and bisphenolic dication form, respectively. High
electrochemical stability and a wide potential range of electroactivity
(0.40–1.30 V vs Ag/Ag+) of the polymer are very
promising for its application as a new electrochromic electrode material
for supercapacitors. That is, an anode composed of poly[meso-Ni(II)-SaldMe]
can serve as an internal charging–discharging indicator in
these supercapacitors.
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Keywords
High electrochemical stabilitybisphenolic dication formcharge transferSchiff base polymer familyPBEelectrochromic electrode materialUVFTIR-ATR spectroelectrochemistry measurementsDFTCVelectropolymerizationcyclic voltammetry conditionsvsquantum chemistry calculationsESRAgelectron-donating phenol moieties
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