Influence of Substituted Pyridine Rings on Physical Properties and Electron Mobilities of 2‐Methylpyrimidine Skeleton‐Based Electron Transporters

Abstract

Abstract A series of 2‐methylpyrimidine skeleton‐based electron‐transporting derivatives (BPyMPM) are designed and synthesized to investigate the influence of substituted pyridine rings on the physical properties and electron mobilities ( μ e ). The only structural difference is the position of substituted pyridine rings. The melting point ( T m) of B4PyMPM is estimated to be ca. 50 °C higher than that of B3PyMPM, and ca. 120 °C higher than that of B2PyMPM. The ionization potential is observed to increase in the order B2PyMPM (6.62 eV) < B3PyMPM (6.97 eV) < B4PyMPM (7.30 eV), measured using ultraviolet photoelectron spectroscopy. Furthermore, time‐of‐fight measurements of vacuum‐deposited films demonstrate that the μ e at 298 K of B4PyMPM is 10 times higher than that of B3PyMPM and 100 times higher than that of B2PyMPM. To extract the charge transport parameters, the temperature and field dependencies of μ e are investigated. Using Bässler's disorder formalism, the degree of energetic disorder is estimated to decrease in the order B2PyMPM (91 meV) > B3PyMPM (88 meV) > B4PyMPM (76 meV), and the positional disorder is 2.7 for B2PyMPM, and < 1.5 for B3PyMPM and B4PyMPM.