Design, synthesis and single-molecular conductivity of isomeric naphthalene diimides

Abstract

Two isomeric 4-methylthiophenylethynyl substituted 1,4,5,8-naphthalene diimide (1,4,5,8-NDI) and 1,2,5,6-naphthalene diimide (1,2,5,6-NDI) derivatives 1 and 2 were designed and synthesized. The physicochemical properties of 1 and 2 were studied by means of UV-vis spectra, electrochemical measurements and DFT calculations. The structural differences between 1 and 2 led to their different physicochemical properties and single-molecule device performance. Compound 1 based on 1,4,5,8-NDI has lower HOMO/LUMO energy levels and narrower band gap, is more conducive to electron transport relative to compound 2 with 1,2,5,6-NDI core. The single molecular junctions of 1 and 2 were prepared by Scanning Tunneling Microscope-Break Junctions (STM-BJ) technique, and their conductive behaviors were studied. When the potential of 0.1 V was applied in the ionic liquid BMIPF6, the conductance of single molecular junctions of 1 and 2 were 10 -3.70 G 0 (15.5 nS) and10 -3.90 G 0 (9.8 nS), respectively, and the single-molecule device based 1 has a better conductivity