Negative Charge Management to Make Fragile Bonds Less Fragile toward Electrons for Robust Organic Optoelectronic Materials

Abstract

The operational stability of organic (opto)electronic devices largely depends on the intrinsic stability of organic materials on service. For organic light-emitting diode (OLED) materials, a key parameter of their intrinsic stability is the bond-dissociation energy of the most fragile bond (BDEf). Although rarely involved, many OLED molecules have the lowest BDEf in anionic states [BDEf(-) ∼1.6-2.5 eV], which could be a fatal short-slab for device stability. Herein, we separated BDEf(-) fromother parameters and confirmed the clear relationship between BDEf(-), intrinsic material stability and device lifetime. Based on thermodynamic principles, we developed a general and effective strategy to greatly improve BDEf(-) by introducing a negative charge manager within the molecule. The manager must combine an electron-withdrawing group (EWG) with a delocalizing structure, so that it can firmly confine the negative charge and hinder the charge redistribution toward fragile bonds. Consequently, the use of this manager can substantially promote BDEf(-) by ∼1 eV for various fragile bonds and outperform the effect reported from solely employing EWGs or delocalizing structures. This effect was verified in typical phosphine-oxide and carbazole derivatives and backed up by newly designed molecules with multiple fragile bonds. This strategy provides a new way to transform vulnerable building blocks into robust organic (opto)electronic materials and devices.