Strategic Synthetic Color Tuning of Oxadiazole Based Luminescent Organoboron Compounds

Abstract

Many organic dopants have been created for use in SMOLED displays, but few are composed of a family of compounds that spans large portions of the visible spectrum. Through careful design, a small family of simple oxadiazole based tetra-coordinated organoboron compounds of the type B(N,O)X has been developed with emission that spans the visible spectrum from violet to green. Oxadiazole based ligands were designed and utilized for their potential for heteroatomic substitution as well as their excellent electron transport properties. Significant changes in fluorescence were observed based on the isomeric substitution of the naphthalene substituent. Minimal bathochromic emission shifts were observed when the oxadiazole ligand was chelated with BPh2, as well as minimal hypsochromic shifts when chelated to BF2. This evidence suggests the emission of the complex is affected by the isomeric position and subsequent resonance of the oxadiazole ligand. Boron clearly forms a dative bond with the lone pair from the nitrogen on the oxadiazole ring. The data shows that this coordination is susceptible to hydrolysis even with the addition of hydrophobic phenyl groups, due to the oxadiazole ring’s inherent electron deficiency and affinity for hydrogen bonding. This is evident especially in the boron trifluoride complex, in which the LCMS data shows the presence of only one fluoride atom.