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Intramolecular π Stacking in Cationic Iridium(III) Complexes with Phenyl‐Functionalized Cyclometalated Ligands: Synthesis, Structure, Photophysical Properties, and Theoretical Studies
Author(s) -
Li Peng,
Shan GuoGang,
Cao HongTao,
Zhu DongXia,
Su ZhongMin,
Jitchati Rukkiat,
Bryce Martin R.
Publication year - 2014
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201400007
Subject(s) - chemistry , iridium , intramolecular force , stacking , cationic polymerization , ruthenium , density functional theory , ligand (biochemistry) , crystallography , octahedral molecular geometry , octahedron , crystal structure , electrochemistry , photochemistry , stereochemistry , computational chemistry , polymer chemistry , catalysis , organic chemistry , biochemistry , receptor , electrode
The syntheses of two new heteroleptic cationic iridium complexes containing 2,6‐diphenylpyridine (Hdppy) and 2,4,6‐triphenylpyridine (Htppy) as the cyclometalated ligands, namely, [Ir(dppy) 2 phen]PF 6 ( 1 , phen = 1,10‐phenanthroline) and [Ir(tppy) 2 phen]PF 6 ( 2 ), are described. The X‐ray crystal structure of 2 reveals a distorted octahedral geometry around the Ir center and close intramolecular face‐to‐face π–π stacking interactions between the pendant phenyl rings at the 2‐position of the cyclometalated ligands and the NN ancillary ligand. This represents a new π–π stacking mode in charged Ir complexes. Complexes 1 and 2 are green photoemitters: their photophysical and electrochemical properties are interpreted with the assistance of density functional theory (DFT) calculations. These calculations also establish that the observed intramolecular interactions cannot effectively prevent the lengthening of the Ir–N bonds of the complexes in their metal‐centered ( 3 MC) states. Complexes 1 and 2 do not emit light in light‐emitting electrochemical cells (LECs) under conditions in which the model compound [Ir(ppy) 2 phen]PF 6 ( 3 ) emits strongly. This is explained by degradation reactions of the 3 MC state of 1 and 2 under the applied bias during LEC operation facilitated by the enhanced distortions in the geometry of the complexes. These observations have important implications for the future design of complexes for LEC applications.