Observation of ultrafast electrons in pendant-embedded conducting two-dimensional polymers

Conducting two-dimensional polymers (C2Ps) are appealing for their extended π-conjugation over the second dimension, yet the exploration of C2Ps with fused aromatic linkages is hindered by strong stacking between adjacent layers. Here, we report a C2P equipped with bulky pendant groups to suppress the interlayer stacking and increase solubility of growth intermediates, resulting in outstanding electrical conductivity after p-type doping. Remarkably, magnetotransport measurements revealed that coherent multi-carrier transport with finite n-type carriers show exceptionally high mobility over 3,200 cm2 V−1 s−1 and long phase coherence length surpassing 100 nm, in stark contrast to hole-carrier transport with 25,000 times lower mobility at low temperatures. This dramatic disparity between electron and hole-carrier transport is attributed to spatially separated electronic states near the Fermi level, which consists of dispersive and flat bands. Our findings highlight the pivotal role of bulky pendant groups in achieving high solubility, Dirac band engineering, and conduction pathway design.