Bipolar Alq3-based complexes: Effect of hole-transporting substituent on the properties of Alq3-center

Two bipolar Alq3-based complexes, tris{5-[(carbazole-9ʹ-yl)methyl]-8-hydroxyquinoline} aluminum (Al(CzHQ)3) and tris{5-[(phenothiazine-9ʹ-yl)methyl]-8-hydroxyquinoline} aluminum (Al(PHQ)3), involving an Alq3-center and three hole-transporting substituents (carbazole or phenothiazine), were prepared and characterized. Effects of hole-transporting substituent on the properties of Alq3-center were investigated in detail. It is found that the two complexes have improved hole-transporting performance and appropriate thermal stability (the 5%-weight-loss temperatures T5%>260 oC). Photoluminescence (PL) spectra indicate that both energy transfer and electron transfer can take place simultaneously in the PL process of these complexes. Both thermodynamics and dynamics of the electron transfer were studied and corresponding parameters were calculated. Energy transfer is favorable for the PL of Alq3-center, while electron transfer is unfavorable for the PL of Alq3-center. These results will be useful to explore novel OLEDs material with increased efficiency.