title: Dynamics of the excited states of [Ir(ppy)2bpy]+ with triple phosphorescence.
abstract: We investigated the relaxation dynamics of bis(2-phenylpyridinato-)(2,2'-bipyridine)iridium(III), [Ir(ppy)(2)bpy](+) using the technique of time-resolved spectroscopy. In the visible emission spectra this molecule exhibits triple phosphorescence: displaying blue, green, and orange bands. From the dependence of spectral shifts with polarity of solvent, decay lifetimes, and the results of calculations using time-dependent density functional theory, we assigned these three emitting states to be triplet interligand charge-transfer ((3)LLCT), metal-to-ligand ppy charge transfer ((3)MLCT(ppy)), and metal-to-ligand bpy charge transfer ((3)MLCT(bpy)) states. The blue states were formed promptly after excitation at wavelength 355 nm; the one lying at higher energy decaying with a time coefficient 0.79-2.56 ns is assigned to be a triplet MLCT, and the other at lower energy decaying in 1.5-2.8 μs is assigned to (3)LLCT(A), A symmetry. This decay time coefficient of (3)LLCT(A) decreases with increasing dielectric constant of the solvent indicating this state mixing of some MLCT character. The green state (3)MLCT(ppy) decays in 0.13-4.8 ns to a nearby intermediate state either (3)MLCT(ppy) or (3)MLCT(bpy). The orange state (3)MLCT(bpy) is coupled to the intermediate state to have a rise time about 0.36-0.84 ns and decays in 425-617 ns. Although many triplet states exist in a small energy range, they couple weakly to display triple emission. All (3)LLCT and (3)MCLT states are coupled to the singlet (1)LLCT manifold directly and/or indirectly and contribute to the emission in the visible range.
authors.affiliation: Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30013, Republic of China.
authors.forename: Shih-Hsiang
authors.initials: SH
authors.lastname: Wu
authors.forename: Jung-Wei
authors.initials: JW
authors.lastname: Ling
authors.forename: Szu-Hsueh
authors.initials: SH
authors.lastname: Lai
authors.forename: Min-Jie
authors.initials: MJ
authors.lastname: Huang
authors.forename: Chien Hong
authors.initials: CH
authors.lastname: Cheng
authors.forename: I-Chia
authors.initials: IC
authors.lastname: Chen
mesh_terms: D015082:2,2'-Dipyridyl / Q000737:chemistry*; D007495:Iridium / Q000737:chemistry*; D049449:Luminescence; D008163:Luminescent Measurements; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet
chemical_list: D009942:Organometallic Compounds; D011725:Pyridines; D007495:Iridium; D015082:2,2'-Dipyridyl