Electrochemical Polymerization of Pyrrole–Perimidine Hybrids: Low-Band-Gap Materials with High n-Doping Activity

Malgorzata Czichy,Halina Zhylitskaya,Mieczyslaw Lapkowski,Maksim Navakouski,Marcin Stępień,Pavel Chulkin,Pawel Zassowski,Patryk Janasik

doi:10.1021/acs.jpcc.0c03002

Abstract

Conductive π-conjugated polymers were electrochemically generated from a variety of donor–acceptor pyrroles containing fused perimidine subunits. Alternating oxidative and reductive polarization of these precursors induces multidirectional coupling involving both perimidine and acenaphtho[1,2-c]pyrrole moieties, producing cross-linked polymeric structures. Chemical oxidation experiments and computational analyses of spin densities in the charged pyrrole intermediates indicate that the formation of inter-perimidine linkages occurs prior to pyrrole–pyrrole couplings. In the resulting polymers, a very stable dication state is achievable with the positive charge located on the bis-perimidine linker. These polymers do not show any stable neutral state and can be easily reduced. Cationic and anionic states of these electrogenerated films were investigated in the solid state by UV–vis–NIR and EPR spectroelectrochemistry, assisted by DFT calculations.

Highlights

Electron-transporting and ambipolar materials are essential components of organic electronic devices such as organic lightemitting diodes (OLEDs),[1] photovoltaic cells (PVCs),[2−5] and organic field-effect transistors (OFETs).[6]
The dication of 1 is a diradical with a triplet ground state (q = +2, m = 3), with the spin density distributed on both parts of the molecule, notably at the 4, 6, 7, and 9 positions of perimidine and at the 7 and 9 positions of acenaphtho[1,2-c]pyrrole (Figure 2, Table S4)
An increase of the spin density is observed for the radical anion and diradical dianion at the 2, 5, 7, and 9 positions of acenaphtho[1,2-c]pyrrole and in the adjacent ring

Summary

Introduction

Electron-transporting and ambipolar materials are essential components of organic electronic devices such as organic lightemitting diodes (OLEDs),[1] photovoltaic cells (PVCs),[2−5] and organic field-effect transistors (OFETs).[6]. The mechanism of ambipolar conductivity is complex and only partly understood, and there are no general methods of achieving this phenomenon in organic materials. Charge carriers in organic semiconductors are trapped by extrinsic species, such as oxygen or water.[12] In addition, the injection of electrons from metals to the organic layer is difficult due to large energetic barriers. These points, do not mean that hole conduction is intrinsically dominant in organic materials. Donor−acceptor systems[13] have been investigated to provide information on charge generation,[14] mechanism of injection, and ambipolar charge transport[15] and to eventually yield materials with increased stability.[16]

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Conclusion