Influence of aggregation on the phosphorescence of iridium complex in poly(methyl methacrylate) matrix

In this study, novel phosphorescent compound of iridium(III)bis(2,3‐diphenylquinoxaline)2‐(benzoimidazol‐2‐yl)pyridine (IrQB) was prepared and the emission study suggests the solid form of IrQB has less phosphorescence intensity than its solution in tetrahydrofuran (THF). To avoid the potential aggregation of IrQB in the concentrated state, poly(methyl methacrylate) (PMMA) was intentionally added as isolator to make solutions of different concentrations in THF and then solid films of IrQB/PMMA of different compositions after THF removal. Films of IrQB/PMMA prepared from dilute solutions exhibit two emission bands centered at 540 and 640 nm, respectively, which is in contrast to the sole 640‐nm emission band observed for films prepared from semidilute solutions. The 540‐ and 640‐nm bands show progressive variations of the intensity with temperature. Emission band at 540 nm is derived from the polarized optical microscope and is attributed to the IrQB aggregates, whose life‐time indicates it is phosphorescent in nature. This aggregate formation is strongly affected by the applied concentrations of IrQB and PMMA in the preparative solution state. Model to postulate the mechanism of aggregate formation in the solution and the derived film states is thereby presented in this study. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 631–639, 2008