Cyclometalated iridium(III) complexes based on phenyl-imidazole ligand

Research output: Contribution to journalArticlepeer-review


  • Etienne Baranoff
  • Simona Fantacci
  • Filippo De Angelis
  • Xianxi Zhang
  • Rosario Scopelliti
  • Michael Grätzel
  • Md Khaja Nazeeruddin

Colleges, School and Institutes

External organisations

  • Istituto Italiano di Tecnologia
  • Laboratory for Photonics and Interfaces
  • Ecole Polytechnique Federale de Lausanne
  • Istituto CNR di Scienze e Tecnologie Molecolari
  • C/o Dipartimento di Chimica
  • Università di Perugia
  • School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, China.
  • School of Basic Sciences
  • Italian Institute of Technology (IIT)
  • Center for Biomolecular Nanotechnologies
  • Liaocheng University


Phenyl-imidazole-based ligands with various substitution patterns have been used as the main ligand for heteroleptic bis-cyclometalated iridium complexes. Two series of complexes have been prepared and their photophysical and electrochemical properties were studied. The phosphorescence emission maxima range from about 490 to 590 nm, that is, from greenish-blue to orange. The first series is of the form Ir(L)2(acac) (L: a phenyl-imidazole based ligand; acac: acetylacetonate). In the first complex, 1a, L is 1,4,5-trimethyl-2-phenyl-1H-imidazole. Then, methyl groups are replaced with phenyl groups and chlorines are grafted on the cyclometalated phenyl ring. The second series is of the form Ir(4,5-dimethyl-1,2-diphenyl-1H-imidazole) 2(La) (La: ancillary ligand being acetylacetonate, acac, N,N-dimethylamino-picolinate, NPic, picolinate, Pic, or 2-(diphenylphosphino)acetic acid, P). These series show that modifying the substitution pattern on the ligands can alter the photophysical and electrochemical properties of the complexes. Overall, we show that compared to complexes containing phenyl-pyridine ligands, highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) are more delocalized over the entire main ligand in complexes containing phenyl-imidazole. Contrary to expectations, when chlorine atoms are used as strong acceptor substituents on the orthometalated phenyl, a red shift of the emission is observed. This behavior has been rationalized using theoretical calculations on the excited state of the chloro-substituted complex 3a compared to the model 1a.


Original languageEnglish
Pages (from-to)451-462
Number of pages12
JournalInorganic Chemistry
Issue number2
Publication statusPublished - 17 Jan 2011