Physical properties of triplet excited states of [Ir(ppy)2bpy](+) in polar solvent and in nonaqueous confined reversed micelle

摘要

The emission properties of the triplet excited states of bis(2-phenylpyridinato-)(2,2'-bipyridine)iridium (III), [Ir(ppy)(2)bpy](PF6) in various solvents and under constrained environment are investigated using technique of time-resolved spectroscopy. This mixed-chelate/ortho-metalate complex has several triplet ligand center and metal-to-ligand charge transfer states in the near ultraviolet to visible range. After 355 nm excitation this triplet emitter exhibits multiple phosphorescent bands in the visible region. Five emission bands are identified, two blue bands with lifetime 1.2-2.1 ns and 1.4-3.1 mu s, respectively assigned to triplet ligand centered charge transfer states (LC)-L-3, two blue-green bands 0.2-0.5 ns and similar to 6 ns assigned to triplet metal-to-ligand charge transfer (MLCTbpy)-M-3 ((3)A) and (MLCTppy)-M-3 (B-3), respectively, and the orange band lying at the lowest energy lifetime 295-620 ns to (MLCTbpy)-M-3 (B-3). These three (MLCT)-M-3 states interact differently in solvent with varied polarity to yield varied features in emission curves. In N,N- dimethylformamide (DMF)/sodium diethylhexyl sulfosuccinate (AOT)/hexane reverse micelle, cavity 1- 3 nm, the (MLCTbpy)-M-3 (B-3) band has shortened lifetime 140-180 ns indicating the polar nature of the environment. In reverse micelle the photoluminescence curve displays broad feature, the blue and green bands with apparent intensity distinct from those in polar solvents. The emission of the orange band (MLCTbpy)-M-3 (B-3) has similar red-shifted feature as that in DMF solution. The other states display large solvatochromic effect in polar cage. Hence, the intense high-energy bands might be because encapsulated in confined environment limits the structural variation of the excited states thus inefficient conversion among them. Relatively less amount of population is cascaded to the lowest energy state (MLCTbpy)-M-3 (B-3). (C) 2015 Elsevier B.V. All rights reserved.