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Iridium(III) Sensitisers and Energy Upconversion: The Influence of Ligand Structure upon TTA‐UC Performance
Author(s) -
Elgar Christopher E.,
Otaif Haleema Y.,
Zhang Xue,
Zhao Jianzhang,
Horton Peter N.,
Coles Simon J.,
Beames Joseph M.,
Pope Simon J. A.
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202004146
Subject(s) - iridium , photon upconversion , ligand (biochemistry) , materials science , chemistry , optoelectronics , doping , organic chemistry , catalysis , biochemistry , receptor
Six substituted ligands based upon 2‐(naphthalen‐1‐yl)quinoline‐4‐carboxylate and 2‐(naphthalen‐2‐yl)quinoline‐4‐carboxylate have been synthesised in two steps from a range of commercially available isatin derivatives. These species are shown to be effective cyclometallating ligands for Ir III , yielding complexes of the form [Ir(C^N) 2 (bipy)]PF 6 (where C^N=cyclometallating ligand; bipy=2,2′‐bipyridine). X‐ray crystallographic studies on three examples demonstrate that the complexes adopt a distorted octahedral geometry wherein a cis ‐C,C and trans ‐N,N coordination mode is observed. Intraligand torsional distortions are evident in all cases. The Ir III complexes display photoluminescence in the red part of the visible region (668–693 nm), which is modestly tuneable through the ligand structure. The triplet lifetimes of the complexes are clearly influenced by the precise structure of the ligand in each case. Supporting computational (DFT) studies suggest that the differences in observed triplet lifetime are likely due to differing admixtures of ligand‐centred versus MLCT character instilled by the facets of the ligand structure. Triplet–triplet annihilation upconversion (TTA‐UC) measurements demonstrate that the complexes based upon the 1‐naphthyl derived ligands are viable photosensitisers with upconversion quantum efficiencies of 1.6–6.7 %.