“Hot exciton” fluorescence and charge transport of fine-tuned twistacenes: theoretical study on substitution effect and intermolecular interactions

Abstract

New twistacene 1 and its CH₃, OH, OCH₃, NH₂, F, CN and NO₂ derivatives were simulated and their photoelectronic and charge transport properties investigated via theoretical calculations. All compounds exhibit blue emission peaks, except 1-NO₂, which emits green/yellow light. Moreover, all compounds, except 1-CN and 1-NO₂, exhibit small singlet–triplet energy gaps, small reorganization energies and large reverse intersystem crossing rate constants between S1 and T2 states, indicating their potential as pure blue “hot exciton” thermally activated delayed fluorescent molecules and sensitizers. In addition, all the twistacenes can be used as n-type transport materials due to their larger intramolecular electron mobilities compared with hole mobilities, regardless of the substituents. Furthermore, all the compounds tend to assemble faster along the L stacking direction due to stronger van der Waals interactions, which has little effect on the UV-visible spectra and makes them stable fluorescent materials. On the other hand, the OH and NH₂ derivatives exhibit good n-type transport properties along the P stacking direction because of higher electron mobilities caused by the intermolecular hydrogen bonds, while the CN and NO₂ derivatives exhibit the largest electron mobilities, along the P1 stacking mode, implying good n-type semiconducting properties. This work demonstrates that the desired optical and conductive properties of twistacenes can be achieved by meticulous simulation of molecular substituents and molecular packing, and thus provides a valuable reference for subsequent molecular design.