Premium
Bis(pyrazol‐1‐yl)methane as Non‐Chromophoric Ancillary Ligand for Charged Bis‐Cyclometalated Iridium(III) Complexes
Author(s) -
Meng Sheng,
Jung Il,
Feng Jie,
Scopelliti Rosario,
Di Censo Davide,
Grätzel Michael,
Nazeeruddin M. Khaja,
Baranoff Etienne
Publication year - 2012
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.201200197
Subject(s) - chemistry , iridium , ligand (biochemistry) , steric effects , photochemistry , excited state , density functional theory , bipyridine , crystallography , stereochemistry , computational chemistry , catalysis , crystal structure , organic chemistry , biochemistry , physics , receptor , nuclear physics
New charged cyclometalated iridium(III) complexes [Ir(ppy) 2 (L)](PF 6 ) [ppy = 2‐phenylpyridine; L = bis(pyrazol‐1‐yl)methane (for 1 ); L = bis(3,5‐dimethylpyrazol‐1‐yl)methane (for 2 )] were synthesized and their electrochemical and photophysical properties studied. These complexes with non‐π‐electron‐conjugated ancillary chelates exhibit significantly blueshifted emission relative to those of commonly used derivatives with NN ancillary ligands such as bipyridine or phenanthroline. Both X‐ray and theoretical analysis based on time‐dependent density functional theory (TD‐DFT) reveal that the binding of Ir to the bis(pyrazol‐1‐yl)methane ancillary ligand is much weaker than that to the phenylpyridine main ligand; the effect is enhanced in the excited state. As a result, the ancillary ligand does not participate in low‐energy excitations and triplet emission, and the electronic transitions are concentrated on the main chromophoric ligands. The blueshift feature is attributed to emission originating from the main cyclometalated ligands, in contrast to emitters with the NN chromophoric ancillary ligand. In addition, complex 2 exhibits a one order of magnitude higher non‐radiative decay rate than complex 1 , which is attributed to the steric hindrance of the methyl groups that leads to a more loosely bound ancillary ligand.