A para-azaquinodimethane integrated quinoidal conjugated microporous polymer

Abstract

Quinoidal compounds own unique properties that make them a promising platform for optoelectronic applications. This has resulted in the development of a plethora of small and one-dimensional (1D) polymers. Surprisingly, there are currently no two-dimensional (2D) analogues available. In this paper, we report the synthesis of a 2D quinoidal-conjugated microporous polymer (Q1) derived from p-azaquinodimethane via Knoevenagel condensation of N,N-diacetyl-piperazine-2,5-dione and tris(4-formylphenyl)amine followed by O-alkylation. The presence of quinoidal p-azaquinodimethane in Q1 improves the π-delocalization within the framework, resulting in a deep red colour, low energy absorption (red edge ∼650 nm) and a bandgap of 1.9 eV. The polymer also enables halochromism to tune the optical bandgap to 1 eV. The p-doped (using iodine vapours) polymer (Q1⁺˙) exhibits high electrical conductivity up to 0.08 s m⁻¹. Most critically, Q1⁺˙ maintains its stability for six days (and beyond) and exhibits stable electrical conductivity, overcoming the low intrinsic stability of such doped materials. This is due to the formation of stable delocalized mixed-valence species assisted by pyrazine formation. This report will spur the development of more quinoidal CMPs and pave the way for overcoming the inherent limitation of poor intra-sheet electron delocalization in 2D polymers.