Europium Coordinate and Covalent Derivatives of Phenanthroline for Intramolecular Carrier Dynamics

Based on the same phenanthroline group, a comparative study of carrier dynamics between small molecules and Eu complexes can understand the influence of nonmetallic elements and metal elements on carrier transport. In this research, two 1,10-phenanthroline derivative materials were designed and prepared, of which one is a small molecule and the other is a europium complex. After conducting basic research on the spectroscopic and electrochemical properties, the carrier mobility curves of the two materials were experimentally measured using the impedance spectroscopy method. The hole and electron mobility of Eu(DBM)3Phen both reached the order of magnitude of 10–4 cm2 V–1 s–1, which is the first time that the highest mobility value has been obtained for Eu complexes in a diode structure. On this experimental basis, the reorganization energy, transfer integral, and carrier mobility were investigated with additional assistance from quantum chemical calculations. Because the molecular size of Eu(DBM)3Phen is larger, the molecule undergoes more pronounced transient structural changes during the carrier transport process. In addition, there is energy transfer from Eu3+ ions to organic ligands. These two factors result in the molecule Eu(DBM)3Phen a larger relaxation energy, that is, a higher reorganization energy value. By deliberately controlling that PhenPy2 and Eu(DBM)3Phen have similar intermolecular carrier transport capabilities, the greater reorganization energy of Eu(DBM)3Phen leads to weaker intramolecular carrier transport capability, which is manifested as lower intramolecular carrier mobility. In our limited knowledge, this is also the first study on the effect of molecular structure on intramolecular carrier mobility, particularly for metal ion coordination.