The effect of non-covalent conformational locks on intra-molecular charge transport of OPV units

Although organic photovoltaic (OPV) molecules containing non-covalent conformational locks (NCLs) are demonstrated with superior device scale charge transport, the NCLs' working mechanism at the molecular level has not been directly addressed or revealed. Herein, three widely used OPV building blocks DT-BT, DT-FBT, and DT-OBT were prepared and comparatively researched for their intra-molecule charge transport (ICT) based on single molecular conductance measurements and theoretical calculation. The measured conductance (G) of the three molecules displays an order of GDT-BT < GDT-FBT < GDT-OBT, contradicting the conductivity order predicted by tunnelling theory. Further research demonstrated that this change was mainly caused by NCLs embedded in DT-FBT and DT-OBT, resulting in more efficient charge transporting pathways, evidenced by their HOMOs showing hyper-conjugation characteristics.