New boron(III) blue emitters for all-solution processed OLEDs: molecular design assisted by theoretical modeling

Luminescent boron (III) complexes have recently been employed as emitters in organic light emitting diodes (OLEDs) with reasonable success. They are easy to prepare and sufficiently stable to be used in such devices, being of great interest as a simple molecular emissive layer. Although emitters for this class with all colors have already been reported, highly efficient and stable blue emitters for applications in solution processed devices still pose a challenge. Here, we report the design, synthesis and characterization of new boron complexes based on the 2-(benzothiazol-2-yl)phenol ligand (HBT), with different donor and acceptor groups responsible for modulating the emission properties, from blue to red. The molecular design was assisted by calculations using our newly developed formalism, where we demonstrate that the absorption and fluorescence spectra can be successfully predicted, being a powerful technique to evaluate molecular photophysical properties prior to synthesis. In addition, density functional theory (DFT) allows to understand the molecular and electronic structure of the molecules in greater detail. The molecules studied here presented fluorescence efficiency as high as Φ = 0.88 and all-solution processed OLEDs were prepared and characterized under ambient atmosphere, after dispersion in the emitting layer. Surprisingly, even considering these rather simple experimental conditions, the blue emitters displayed superior properties compared to present literature, in particular with respect to the current efficiency stability.