How to Make Fragile Bonds no Longer Fragile Towards Electrons for Robust Organic Optoelectronic Materials
The development of robust organic (opto)electronic devices is mainly hindered by the chemical deterioration of organic materials on service. For organic light-emitting diode (OLED) materials, a key molecular parameter for intrinsic chemical stability is the bond-dissociation energy of the fragile bond (BDEf) with the lowest BDE in the molecule. Although rarely concerned, most OLED molecules have the lowest BDEf in negatively charged states (BDEf(−), ∼1.6−2.5 eV), which would be a fatal short-slab for device stability. Here, we confirmed the close correlation between BDEf(−), intrinsic material stability, and device lifetime. To make fragile bonds no longer fragile towards electrons, we found that introducing strong electron-withdrawing groups with delocalizing structures would be an effective and universal strategy, which was found in typical phosphine-oxide and carbazole module molecules and backed by comparisons in several reported and newly designed molecules. It not only substantially improves BDEf(−) by ∼1 eV, but revives the originally vulnerable building blocks, thus largely enriches available groups for rational design of robust OLED and other organic (opto)electronic materials.