Asymmetric side-chain engineering of organic semiconductor for ultrasensitive gas sensing

Molecular structure of organic semiconductor plays a critical role in determining the performance and functionality of organic electronic devices, by optimizing the electrical, optical and physicochemical properties. Substituted alkyl chains are fundamental units in tailering the solubility and assemblability, among which the asymmetric properties have been reported as key element for controlling the packing motifs and intrinsic charge transport. Here, we expanded the scope of molecular asymmetry dependent sensing features based on a new series of naphthalene diimides (NDI)-based derivatives substituted with a same branching alkyl chain but various linear-shaped alkyl chains (Cn-). A clear molecular stacking change, from head-to-head bilayer to head-to-tail monolayer packing model, is observed based on the features of anisotropic molecular interactions with the change in the chain length. Most importantly, a unique LUMO level shift of 0.17 eV is validated for NDI-PhC4, providing a record sensitivity up to 150% to 0.01 ppb ammonia, due to the desired molecular reactivity and device amplification properties. These results indicate that asymmetric side-chain engineering opens a route for breath healthcare.