Heteroleptic Cyclometalated Iridium(III) Complexes Supported by Triarylborylpicolinate Ligand: Ratiometric Turn-On Phosphorescence Response upon Fluoride Binding

Abstract

Heteroleptic cyclometalated iridium(III) complexes (C^N)2Ir(Bpic) (4-6) (C^N = dfppy (4), ppy (5), btp (6)) supported by triarylborylpicolinate (Bpic) ancillary ligand were synthesized and characterized. X-ray diffraction study of 5 confirmed N^O chelation of the Bpic ligand to the iridium center forming an (C^N)2Ir-borane conjugate. While the UV/vis absorption bands of 4-6 remained almost unchanged in the low-energy region upon fluoride addition, a ratiometric turn-on phosphorescence response was observed for 4 and 5. In contrast, the phosphorescence of 6 was little affected by fluoride binding. Experimental and theoretical studies suggest that the LUMO in neutral 4 and 5 is dominated by the Bpic ligand, which makes the weakly emissive (3)ML'CT/(3)LL'CT (L = C^N; L' = Bpic) states as the lowest-energy triplet excited state, while the fluoride binding to 4 and 5 induces the highly emissive (3)MLCT/(3)ππ* states centered on the (C^N)2Ir moiety. Thermally induced conversion from the (3)MLCT/(3)ππ* to the (3)ML'CT/(3)LL'CT states is suggested to be responsible for the low-energy weak phosphorescence in 4 and 5.

A unique iridium(III) complex-based chemosensor for multi-signal detection and multi-channel imaging of hypochlorous acid in liver injury

“…Lowest-energy triplet excited state (T 1 ) of Ir-COOH was contributed from HOMO → LUMO, which can be attributed to the emissions of 3 MLCT and 3 LLCT, as has usually been demonstrated in the Ir(III) complexes (Ru et al 2014;Sharma et al 2014;Xiong et al 2010). In contrast, the inefficient luminescence emission of Ir-Fc may be assigned to the 3 ILCT, 3 LMCT and 3 LLCT based on HOMO-1 → LUMO+7 and HOMO → LUMO+9.…”

“…In contrast, the inefficient luminescence emission of Ir-Fc may be assigned to the 3 ILCT, 3 LMCT and 3 LLCT based on HOMO-1 → LUMO+7 and HOMO → LUMO+9. These transitions may be attenuated by the electron transfer from Fc moiety to bpy ligand, leading to the luminescence quenching of Ir-Fc (Sharma et al 2014). This feather of lack of excited state is in parallel with the electrochemical analysis for Ir-Fc.…”

Boron‐Functionalized Phosphorescent Iridium(III) Complexes

“…To advance the design of turn‐on‐type F – probes based on Ir III –boron complexes further, Lee et al designed the TAB‐modified picolinate ligand (Bpic) and synthesized the three heteroleptic Ir III complexes 6 , 7 , and 8 {with dfppy [2‐(4,6‐difluorophenyl)pyridine], ppy, and btp, respectively, as C ^ N ligands; Scheme } . These three complexes showed different emission spectra and F – ‐sensing abilities.…”

Triarylborane Lewis acids with indole or phenol group: B/H hybrid receptors for fluoride

“…The absorption band was almost completely quenched upon addition of one equiv of fluoride. The resulting fluoride binding constant (K) of 1, estimated from the 1:1 binding isotherm [50,62,67,82], was very high and was equal to 4.0 Â 10 7 M À1 in DMSO. To elucidate whether the fluoride binding affinity was enhanced by the presence of an NeH hydrogen bond donor, we compared the fluoride binding properties with those of the Mes 2 BPh (3) compound (Fig.…”