The Effect of Weak Π-Π Interactions on Single-Molecule Electron Transport Properties of the Tetraphenylethene Molecule and Its Derivatives: a First-Principles Study.

Intramolecular pi-pi interactions are a significant research focus in fields such as chemistry, biology, and materials science. Different configurations of benzene-benzene moieties within a molecule can affect the magnitude of their pi-pi interactions, consequently influencing the electronic transport capabilities of the molecule. In this study, we designed three pi-conjugated molecules, TPEM, TPEEM, and TEEPM, based on tetraphenylethene (TPE). These three molecules exhibit three distinct pi-conjugated structures: linear cis-pi-conjugation, linear trans-pi-conjugation, and cross-pi-conjugation. Thereinto, TPEM and TPEEM molecules share the same TPE core, with identical pi-pi interaction distances, while the TEEPM molecule has acetylene groups between the TPE units, thereby increasing the pi-pi interaction distances between the benzene moieties. Using density functional theory calculations combined with non-equilibrium Green's function (DFT+NEGF), our results reveal that the conductance order of different pi-conjugated structures in TPEM and TPEEM molecules is as follows: cis > cross approximate to trans. Through analysis of transmission spectra, transmission pathways, and the innermost pi orbitals, we find that in TPEM and TPEEM molecules, the cis- and cross-pi-conjugated structures exhibit pi-pi interactions between benzene moieties and provide special through-space electron transport pathways, enhancing their electronic transport capabilities in coordination with the bonded molecular framework, whereas their trans-conjugated structures only allow electron transport along the molecular backbone. In contrast, in TEEPM molecule, due to the absence of pi-pi interactions, the conductance of different pi-conjugated structures is primarily determined by the molecular backbone and follows the order: trans > cis > cross. These findings provide a theoretical basis for designing single-molecule electronic devices with multiple electron channels based on intramolecular pi-pi interactions.