Dual luminescence, interligand decay, and nonradiative electronic relaxation of cyclometalated iridium complexes in solution

Fabrizio Messina, Enrico Pomarico, Mahsa Silatani, Braem, Klein, Barranoff, Majed Chergui, Andrea Cannizzo, Fabrizio Messina, Lambert

Risultato della ricerca: Articlepeer review

28 Citazioni (Scopus)

Abstract

Femtosecond broadband photoluminescence studies are presented for Ir(ppy)3 (Ir1), Ir(ppy)2(pic) (Ir2), Ir(ppy)2(bpy)(PF6) (Ir3), Ir(ppz)3 (Ir4), and Ir(ppz)2dipy (Ir5) (where ppy = 2-phenylpyridine, pic = picolinate, bpy = 2,2′-bipyridine, ppz = 1-phenylpyrazole, and dipy = 5-phenyldipyrrinato) in solution. Upon 400-nm excitation of Ir1-Ir3, we observed a prompt population of the lowest MLCT states. The higher states decay on an ultrafast time scale (<100 fs), whereas the lowest 3MLCT state undergoes further vibrational relaxation on a 1-ps time scale. In Ir3, this relaxation is accompanied by an interligand decay from the ppy to the bpy ligand in ∼1.5 ps. For the ppy-containing complexes (Ir1 and Ir2), we found that, at 100 ps, the luminescence is red-shifted with respect to the steady-state emission. This is explained in terms of a time-delayed dual luminescence, which we attribute to a double-well minimum configuration of the lowest emitting triplet states involving the ppy moiety. Ir4 shows a prompt population of the lowest excited state, which then undergoes vibrational relaxation in ∼0.5 ps. Finally, at short times, Ir5 exhibits fluorescence from the lowest 1LC state, which decays in ∼100 fs to the manifold of 3LC states. Overall, this study shows that, although the ultrafast relaxation to the lowest electronic states is quite similar to that of other transition-metal complexes, most of the differences occur at the lowest emissive states, with effects such as time-delayed dual fluorescence, interligand decay, and nonradiative relaxation to the ground or lower-lying metal-centered states. Understanding these effects is crucial for obtaining optimal performances of iridium complexes, calling for further iterations between chemical synthesis and photophysical studies to optimize these complexes.
Lingua originaleEnglish
pagine (da-a)16459-16469
Numero di pagine11
RivistaJOURNAL OF PHYSICAL CHEMISTRY. C
Volume120
Stato di pubblicazionePublished - 2016

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • ???subjectarea.asjc.2100.2100???
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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