TY - JOUR
T1 - Structure-property relationships based on Hammett constants in cyclometalated iridium(iii) complexes
T2 - Their application to the design of a fluorine-free FIrPic-like emitter
AU - Frey, Julien
AU - Curchod, Basile F E
AU - Scopelliti, Rosario
AU - Tavernelli, Ivano
AU - Rothlisberger, Ursula
AU - Nazeeruddin, Mohammad K.
AU - Baranoff, Etienne
PY - 2014/4/21
Y1 - 2014/4/21
N2 - While phosphorescent cyclometalated iridium(iii) complexes have been widely studied, only correlations between oxidation potential EOX and Hammett constant σ, and between the redox gap (ΔEREDOX = EOX - ERED) and emission or absorption wavelength (λabs, λem) have been reported. We present now a quantitative model based on Hammett parameters that rationalizes the effect of the substituents on the properties of cyclometalated iridium(iii) complexes. This simple model allows predicting the apparent redox potentials as well as the electrochemical gap of homoleptic complexes based on phenylpyridine ligands with good accuracy. In particular, the model accounts for the unequal effect of the substituents on both the HOMO and the LUMO energy levels. Consequently, the model is used to anticipate the emission maxima of the corresponding complexes with improved reliability. We demonstrate in a series of phenylpyridine emitters that electron-donating groups can effectively replace electron-withdrawing substituents on the orthometallated phenyl to induce a blue shift of the emission. This result is in contrast with the common approach that uses fluorine to blue shift the emission maximum. Finally, as a proof of concept, we used electron-donating substituents to design a new fluorine-free complex, referred to as EB343, matching the various properties, namely oxidation and reduction potentials, electrochemical gap and emission profile, of the standard sky-blue emitter FIrPic.
AB - While phosphorescent cyclometalated iridium(iii) complexes have been widely studied, only correlations between oxidation potential EOX and Hammett constant σ, and between the redox gap (ΔEREDOX = EOX - ERED) and emission or absorption wavelength (λabs, λem) have been reported. We present now a quantitative model based on Hammett parameters that rationalizes the effect of the substituents on the properties of cyclometalated iridium(iii) complexes. This simple model allows predicting the apparent redox potentials as well as the electrochemical gap of homoleptic complexes based on phenylpyridine ligands with good accuracy. In particular, the model accounts for the unequal effect of the substituents on both the HOMO and the LUMO energy levels. Consequently, the model is used to anticipate the emission maxima of the corresponding complexes with improved reliability. We demonstrate in a series of phenylpyridine emitters that electron-donating groups can effectively replace electron-withdrawing substituents on the orthometallated phenyl to induce a blue shift of the emission. This result is in contrast with the common approach that uses fluorine to blue shift the emission maximum. Finally, as a proof of concept, we used electron-donating substituents to design a new fluorine-free complex, referred to as EB343, matching the various properties, namely oxidation and reduction potentials, electrochemical gap and emission profile, of the standard sky-blue emitter FIrPic.
UR - http://www.scopus.com/inward/record.url?scp=84896459762&partnerID=8YFLogxK
U2 - 10.1039/c3dt52739e
DO - 10.1039/c3dt52739e
M3 - Article (Academic Journal)
C2 - 24345847
AN - SCOPUS:84896459762
SN - 1477-9226
VL - 43
SP - 5667
EP - 5679
JO - Dalton Transactions
JF - Dalton Transactions
IS - 15
ER -