“…With the coplanar geometry and excellent p-electron delocalization feature,l adder-type heteroarenes have recently emerged as promising organic semiconductors with excellent device performance. [1,28,29] In this context, we design and synthesize two novel nonfullerene acceptors (M8 and M34 in Scheme 1) based on different heterocycles-based ladder-type heteroheptacenes both of which are free of sp 3 carbon atom. Thet wo pairs of neighboring side chains on the heteroheptacene are used to suppress the immoderate intermolecular aggregation thereby leading to suitable phase separation with optimal domain sizes.M8and M34 share the same A-D-A configuration with the identical side-chains as well as the same ending groups of 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile,b ut they differ in the aromaticity of the central electron-donating core.W ith the larger size of sulfur in the thiophene unit in relative to oxygen in the furan unit, the thiophene heterocycleh as an enhanced resonance energy of 121 kJ mol À1 compared to the furan heterocycle (67 kJ mol À1 ) [30] which may lead to al arger aromatic stabilization energy (increased aromaticity index) of the corresponding electron-donating core based on the thiophene heterocycles.Replacement of the furan heterocycles with the thiophene heterocycles in the heteroheptacene does not affect the molecular orientation and p-p-stacking distance of the resulting nonfullerene acceptors,b ut the replacement leads to hypsochromically shifted absorption, improved charge transport, and molecular orientation change in the blend film.…”