Naphthalimide end capped anthraquinone based solution-processable n-channel organic semiconductors: effect of alkyl chain engineering on charge transport

Abstract

Herein, we are reporting the synthesis, characterization and organic field effect transistor characteristics of a new class of 1,8-naphthalimide (NAI) and 9,10-anthraquinone (ANQ) strong electron withdrawing group based n-channel small molecule semiconductors with different branched alkyl chain length, namely NAI-ANQ-NAI (BO), NAI-ANQ-NAI (HD), and NAI-ANQ-NAI (DT). All three small molecules exhibit different solubility behavior based on their alkyl chain length in common organic solvents. NAI-ANQ-NAI (BO), NAI-ANQ-NAI (HD), and NAI-ANQ-NAI (DT) show quite deep LUMO energy levels (around −4.2 eV) which is promising for better air-stable electron transport. Under ambient atmosphere, we found that electron mobilities of solution-processed thin-film transistors based on these small molecules were enhanced when annealing temperature increased from 140 to 200 °C due to better thin film microstructures. At 200 °C, devices exhibited the best performances with the maximum electron mobilities of 2.79 × 10⁻², 2.09 × 10⁻² and 2.40 × 10⁻² cm² V⁻¹ s⁻¹ for NAI-ANQ-NAI (BO), NAI-ANQ-NAI (HD) and NAI-ANQ-NAI (DT), respectively. The spin-coated films of these materials exhibited quite smooth and uniform morphology although these are small molecules forming crystalline structures. These results clearly demonstrate that the fused anthraquinone and naphthalimide are potential functional moieties for constructing solution processable electron transporting materials for organic and printed electronics.