Synthesis, Charge Transport and Photophysical Properties of Novel Disubstituted Silylethyne Acenes

Rubrene has long been the gold standard among molecular organic semiconductors, with champion mobility and unique and exploitable photophysical properties such as facile triplet-triplet annihilation. Like rubrene, the silylethyne acenes are also π-stacked, but do not adopt the unique combination of face-to-face and edge-to-face interactions that minimize short-axis slip and maximize π-stacking interactions. We have explored several simple approaches to minimize short-axis slip issues, and now have set our sights on synthetic modifications to generate soluble, solution-processable acenes and heteroacenes which assemble in rubrene-like motifs. I will show that careful selection and placement of substituents on silylethyne pentacenes cause the backbone to either twist or bow. Surprisingly, these relatively bulky pendant groups still permit strong π-stacking interactions, with the twisted chromophores adopting the 'brickwork' packing common to silylethyne acenes, and the bowed chromophores adopting rubrene-like packing, with similarly limited short-axis offsets. Initial device studies show promising charge transport properties, despite the heavily distorted chromophores. More surprising, these added substituents, even though they are not conjugated to the chromophore, have substantial impact on the molecules' photophysical properties, while simultaneously dramatically improving material stability. Simple, synthetically-scalable approaches to form acene-based singlet fission chromophores with vastly improved stability will also be discussed.