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

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 (P1andP2) and fused (P3andP4) bis-IIDs on the backbone lead to varied conformational flexibility that dominates aggregation, energy levels, and packing of the polymers.P3andP4with a planar backbone exhibit a stronger aggregation and lower bandgap (1.38 eV) thanP1andP2(∼1.8 eV), while their intense non-crystalline aggregation also results in an amorphous structure. Meanwhile, the configurational differences arising from axisymmetric T unit (P1andP3) and centrosymmetric TT unit (P2andP4) spacers is shown to deeply affect the surface morphology and film ductility. The non-planar backbone endowsP1andP3with low surface roughness and high brittleness. The combined low conformation and configuration regularity account for the inferior mobility ofP1. On the contrary,P2-P4exhibit comparable hole mobility ranging from 10⁻²-10⁻³cm²V⁻¹s⁻¹and up to 0.011 cm²V⁻¹s⁻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.