Investigating the backbone conformation and configuration effects for donor–acceptor conjugated polymers with ladder-type structures synthesized through Aldol polycondensation

Abstract

Aldol reaction is a green approach that is exclusively suitable for developing conjugated polymers (CPs) with ladder-type structures. Herein, electron-deficient non-fused and fused bis-isoindigo (bis-IID) are copolymerized with axisymmetric thiophene (T) or centrosymmetric thieno[3,2-b]thiophene (TT) electron-rich spacers through Aldol polycondensation to prepare four donor–acceptor (D–A) CPs with ladder-type structures. The non-fused (P1 and P2) and fused (P3 and P4) bis-IIDs on the backbone lead to varied conformational flexibility that dominates aggregation, energy levels, and packing of the polymers. P3 and P4 with a planar backbone exhibit a stronger aggregation and lower bandgap (1.38 eV) than P1 and P2 (∼1.8 eV), while their intense non-crystalline aggregation also results in an amorphous structure. Meanwhile, the configurational differences arising from axisymmetric T unit (P1 and P3) and centrosymmetric TT unit (P2 and P4) spacers is shown to deeply affect the surface morphology and film ductility. The non-planar backbone endows P1 and P3 with low surface roughness and high brittleness. The combined low conformation and configuration regularity account for the inferior mobility of P1. On the contrary, P2–P4 exhibit comparable hole mobility ranging from 10⁻²–10⁻³ cm² V⁻¹ s⁻¹ and up to 0.011 cm² V⁻¹ s⁻¹ (P2), due to their better regularity in both conformation and configuration. Collectively, our results provide a new perspective for designing new D–A CPs through Aldol polycondensation.