Cross-dipole π-π stacking of crossed perylene diimides with D-A-D structures by crystal engineering towards ambipolar charge transport performance and aggregation-induced emission

Abstract

A cross-dipole π-π close-stacking of 1,7-diphenylazophenol (AZO) perylene diimides (PDI, AZO-PDIs) formed in a single-crystal integrating good ambipolar charge transport and aggregation-induced emission (AIE) behaviors has been unveiled. The weak electron donating and moderate steric hindrance of AZOs endows AZO-PDIs with crossed Donor-Acceptor-Donor (D-A-D) structures, which facilitates the charge injection of both electrons and holes and a distinct cross-dipole π-π close-packing with the distance of only 3.29 Å. Accordingly, the wave function overlaps and electronic coupling of PDI cores are significantly enhanced to provide a quasi-1D charge transport channel, resulting in ambipolar performance with the hole and electron mobility of 6.74 cm2 V−1 s−1 and 5.96 cm2 V−1 s−1 respectively. The average conductivity of 0.5 S m−1 has further confirmed the good charge transport properties of the single crystals. Moreover, it also exhibits AIE behaviors due to the weak transition dipole resonance induced by the cross-dipole stacking of a large rotation angle (79.8°) and restriction of intramolecular rotation of the bulk AZOs. This work initially provides a promising strategy for achieving both charge transport and AIE performance on account of D-A-D molecules with crossed conformations at the molecular level and efficient π-overlaps induced by cross-dipole stacking at the supramolecular level.