Unusual Doping of Donor–Acceptor-Type Conjugated Polymers Using Lewis Acids

Conjugated polymers that can undergo
unusual nonoxidative doping
were designed. A series of polymers based on donor–acceptor–donor
(DAD) moieties 2,1,3-benzoselenadiazole, 2,1,3-benzothiadiazole, 2,1,3-benzoxadiazolebenzo­[2,1,5]­oxodiazole,
and 2-hexylbenzotriazole as acceptor fragments and 3,4-ethylenedioxyselenophene
(EDOS) and 3,4-ethylenedioxythiophene (EDOT) as donor fragments was
prepared. When the studied polymers were reacted with Lewis acids
and bases, notable optical switching and conductivity changes were
observed, evidencing the exceptional case of efficient nonoxidative
doping/dedoping. Remarkably, in previously reported works, coordination
of Lewis acids causes band gap shift but not doping of the conductive
polymer, while in the present study, coordination of Lewis acid to
highly donating EDOT and EDOS moieties led to polymer doping. The
polymers show remarkable stability after numerous switching cycles
from neutral to doped states and vice versa and can be switched both
electrochemically and chemically. The reactivity of the prepared polymers
with Lewis acids and bases of different strengths was studied. Calculation
studies of the Lewis acid coordination mode, its effect on polymer
energies and band gap, support the unusual doping. The reported doping
approach opens up the possibility to control the conjugation, color
change, and switching of states of conjugated polymers without oxidation.