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.
The Raman and infrared spectra of fac-tris(2-phenylpyridinato-N,C2 )iridium(III), Ir(ppy) 3 and surface-enhanced resonance Raman spectra of bis(2-phenyl pyridinato-) (2,2 bipyridine) iridium (III), [Ir(ppy) 2 (bpy)] + cation were recorded in the wavenumber range 150-1700 cm −1 , and complete vibrational analyses of Ir(ppy) 3 and [Ir(ppy) 2 (bpy)] + were performed. Most of the vibrational wavenumbers were calculated with density-functional theory agree with experimental data. On the basis of the results of calculation and comparison of the spectra of both complexes and their analogue [Ru(bpy) 3 ] 2+ , we assign the vibrational wavenumbers for metal-ligand modes; metal-ligand stretching wavenumbers are 277/307 and 261/236 cm −1 for Ir(ppy) 3 , and 311/324, 257/270, 199/245 cm −1 for [Ir(ppy) 2 bpy] + . Surface-enhanced Raman scattering spectra of [Ir(ppy) 2 bpy] 2+ were measured at two wavelengths on the red and blue edges of the low-energy metal-to-ligand charge-transfer band. According to the enhanced Raman intensities for the vibrational modes of both ligands ppy and bpy, the unresolved charge-transfer band is deduced to consist of charge-transfer transitions from the triplet metal to both ligands ppy and bpy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.