Rational utilization of intramolecular and intermolecular hydrogen bonds to achieve desirable electron transporting materials with high mobility and high triplet energy

Three new pyrimidine-containing star-shaped compounds, namely, 1,3,5-tri(3-(pyrimidin-5-yl)phenyl)benzene (TPM-TPB), 2,4,6-tris(3-(pyrimidin-5-yl)phenyl)-1,3,5-triazine (TPM-TAZ) and 3,5,6-tris(3-(pyrimidin-5-yl)phenyl)-1,2,4-triazine (TPM-i-TAZ), were synthesized and characterized. These new compounds exhibited favorable electronic affinity (E_a >2.81 eV) and the triplet energy levels (E_T) up to ∼2.83 eV. X-ray diffraction analysis of the compounds revealed that the intramolecular and intermolecular C-H·N hydrogen bonds of TPM-TAZ resulted in high electron mobility up to 2.0 × 10^-3 cm² V^-1 s^-1. Using these compounds as the electron transporting materials, the blue phosphorescent organic light-emitting devices showed good performance, with a very low turn-on voltage of 2.4 V, a maximum current efficiency of 26.4 cd A^-1, and a maximum power efficiency of 26.9 lm W^-1.