High-Throughput Screening and Automated Data-Driven Analysis of the Triplet Photophysical Properties of Structurally Diverse, Heteroleptic Iridium(III) Complexes

Abstract

Steady state emission spectra and excited state lifetimes were measured for 1440 distinct heteroleptic [Ir­(C^N)2(N^N)]+ complexes prepared via combinatorial parallelized synthesis; 72% of the complexes were found to be luminescent, and the emission maxima of the library spanned the visible spectrum (652–459 nm). Spectral profiles ranged from broad structureless bands to narrow emissions exhibiting vibrational substructure. Measured excited state lifetimes ranged between ∼0.1–14 μs. Automated emission spectral fitting with successive Gaussian functions revealed four distinct measured classes of excited states; in addition to well understood metal–ligand to ligand-charge transfer (3MLLCT) and ligand-centered (3LC) excited states, our classification also identified photophysical characteristics of less explored mixed 3MLLCT/3LC states. Electronic structure features obtained from DFT calculations performed on a large subset of these Ir­(III) chromophores offered clear insights into the excited state properties and allowed the prediction of structure/luminescence relationships in this class of commonly used photocatalysts. Models with high prediction accuracy (R2 = 0.89) for emission color were developed on the basis of experimental data. Furthermore, different degrees of nuclear reorganization in the excited state were shown to significantly impact emission energy and excited state lifetimes.

Luminescence properties of [Ir(C^N)2(N^N)]+ complexes: relations between DFT computation results and emission band-shape analysis data

“…In nice agreement with the literature data, [82][83][84][85][86][87][88][89] the presence of different C^N and N^N ligands in the [Ir(C^N) 2 (N^N)] + structures differentiates to some extent their UV-Vis absorption spectra. The effects, however, are relatively small as it can be clearly seen in the representative examples depicted in Fig.…”

“…À salts according to literature procedures. [82][83][84][85][86][87][88][89] The obtained reaction products were further puried by means of column chromatography on (silica gel with CH 2 Cl 2 as the eluent, changing next to acetone : CH 2 Cl 2 1 : 30 or 1 : 10 v/v). The…”

“…Some of these chelates have been already tested as potential materials for OLED devices and their luminescence were reported in the literature. [82][83][84][85][86][87][88][89] Whereas the [Ir(ppz) 2 (N^N)] + complexes [82][83][84][85][86] exhibit typically the MLCT emission, their [Ir(dfppz) 2 (N^N)] + counterparts [87][88][89] display, for some of the N^N ligands, the 3 *N^N ligand centred LC emission. From this point of view, one can regard the mentioned Ir 3+ chelates as particularly well designed model systems allowing testing the raised hypothesis for similar as well as different enough emitters.…”

Fluorescence Imaging and Photodynamic Inactivation of Bacteria Based on Cationic Cyclometalated Iridium(III) Complexes with Aggregation‐Induced Emission Properties

“…[ 29 ] The triplet state (T 1 )‐to‐ground state (S 0 ) radiative decay (i.e., phosphorescence centered at ≈650 nm) is either originated from an entirely triplet ligand‐centered lowest‐lying excited state ( 3 LC) or a mixed 3 MLLCT/ 3 LC excited state after an internal conversion, in which the T 1 composition nature is dependent of the relative energies of both 3 MLLCT and 3 LC excited states. [ 25 ]…”

“…The specific diimine co‐ligand was chosen to lower the energy levels of LUMO among the metal complexes, hence reducing the HOMO–LUMO gap (i.e., equivalent to increasing UV–Vis absorption wavelength) of the metal complexes due to the substituted electron‐withdrawing phosphonate esters. [ 25 ] In addition to the fundamental understanding of the photophysical properties and photochemistry, these three red photosensitizers were minutely examined in fluorescence imaging and visible light photodynamic inactivation of bacteria.…”