Silole derivatives: relationships between molecular arrangement and OLED efficiency.

The goal of the present study is to underline the relationships that may exist between the molecular arrangement in thin films and the OLED efficiency. For this purpose, we have synthesized three new silole derivatives with incrementally flexible structure to tune their packing ability. Moreover, these siloles were especially designed to possess both electron-and hole-transporting properties in order to be used in single-layer OLEDs. This architecture was chosen since the absence of organic layers interfaces allows a better evaluation of the role of the molecular arrangement in the active layer. The examination of the EL properties gives evidences of the prominent role of the molecular organization on the OLED efficiency. A crystalline-like organization of the molecules allows high current density but low luminance efficiency since an excessive electron current flow is involved compared to the hole one, and the recombination rate is poor. On the contrary, disordered assemblies of molecules allows better performances by avoiding unfavorable p-stacking, while keeping good intermolecular orbital overlaps to support charge carrier transport. Thus single-layer devices based on silole 9 exhibit luminance efficiency as high as 0.75 Cd/A associated with both good chemical and film stabilities that are very promising applications for long life OLED application.