Multinuclear 2-(Quinolin-2-yl)quinoxaline-Coordinated Iridium(III) Complexes Tethered by Carbazole Derivatives: Synthesis and Photophysics

Abstract

Five mono/di/trinuclear iridium­(III) complexes (1–5) bearing the carbazole-derivative-tethered 2-(quinolin-2-yl)­quinoxaline (quqo) diimine (N^N) ligand were synthesized and characterized. The photophysical properties of these complexes and their corresponding diimine ligands were systematically studied via UV–vis absorption, emission, and transient absorption (TA) spectroscopy and simulated by time-dependent density functional theory. All complexes possessed strong well-resolved absorption bands at <400 nm that have predominant ligand-based 1π,π* transitions and broad structureless charge-transfer (1CT) absorption bands at 400–700 nm. The energies or intensities of these 1CT bands varied pronouncedly when the number of tethered Ir­(quqo)­(piq)2 + (piq refers to 1-phenylisoquinoline) units, π conjugation of the carbazole derivative linker, or attachment positions on the carbazole linker were altered. All complexes were emissive at room temperature, with 1–3 showing near-IR (NIR) 3MLCT (metal-to-ligand charge-transfer)/3LLCT (ligand-to-ligand charge-transfer) emission at ∼710 nm and 4 and 5 exhibiting red or NIR 3ILCT (intraligand charge-transfer)/3LMCT (ligand-to-metal charge-transfer) emission in CH2Cl2. In CH3CN, 1–3 displayed an additional emission band at ca. 590 nm (3ILCT/3LMCT/3MLCT/3π,π* in nature) in addition to the 710 nm band. The different natures of the emitting states of 1–3 versus those of 4 and 5 also gave rise to different spectral features in their triplet TA spectra. It appears that the parentage and characteristics of the lowest triplet excited states in these complexes are mainly impacted by the π systems of the bridging carbazole derivatives and essentially no interactions among the Ir­(quqo)­(piq)2 + units. In addition, all of the diimine ligands tethered by the carbazole derivatives displayed a dramatic solvatochromic effect in their emission due to the predominant intramolecular charge-transfer nature of their emitting states. Aggregation-enhanced emission was also observed from the mixed CH2Cl2/ethyl acetate or CH2Cl2/hexane solutions of these ligands.

Amplifying Photoluminescence of Lanthanide-Doped Nanoparticles by Iridium Phosphonate Complex

“…When NaYF 4 :Nd@ Ir1 and NaYF 4 @ Ir1 were excited by 355 nm light, similar transient absorption spectra, with a broad absorption band mainly centred at ∼388 nm and a negative band centered at ∼565 nm, were obtained (Figure b and Figure S25). The absorption and negative bands can be assigned to the triplet absorption of Ir1 and the stimulated emission from Ir1 , respectively. − The transient absorption spectra and decay of the excited-state absorption at different wavelengths (Table S4), together with the luminescence decay of Ir1 (Figure a), reveal that the excited-state absorption and luminescence of Ir1 , observed under our conditions, should arise from the same triplet excited state. Notably, taking the decay of the excited-state absorption of Ir1 at 388 nm as an example, we observed a much shortened lifetime in NaYF 4 :Nd@ Ir1 when compared with that in NaYF 4 @ Ir1 (Figure c and Table S4), which is in agreement with the luminescence lifetimes of Ir1 in the same samples (Figure a and Table S4).…”

Combined Machine Learning, Computational, and Experimental Analysis of the Iridium(III) Complexes with Red to Near-Infrared Emission

“…In contrast, the choice of applied functional strongly impacts the optical spectra. For example, long-range corrected functionals, such as wB97XD, usually exhibit over-blue-shifted absorption bands compared to related experimental spectra. − Therefore, we have chosen the hybrid PBE0 functional for our calculations, because it shows a good compromise in the accuracy of the ground- and excited-state calculations, as evidenced by comparison with experimental data. ,,,− …”

Functionalized C3-Symmetric Building Blocks—The Chemistry of Triaminotrimesic Acid

“…[ 5 ]). The applications range from discotic liquid crystals [ 6 , 7 ]; mesogens [ 8 ]; OLED emitters featuring thermally-activated delayed fluorescence; [ 9 , 10 , 11 ] gels; [ 12 ] metal-organic frameworks (MOFs) (trimesic acid/BTC: MOF-177 [ 13 ]; MOF-199; 2D-covalent organic frameworks (COFs) [ 14 , 15 ]; hole-transporting materials for photovoltaics; [ 16 ] materials for second harmonic generation/non-linear optics by generating octopoles [ 17 , 18 , 19 ]; hydrogels [ 20 , 21 ] and many more [ 22 ]. Noteworthy in this context are functionalized truxenes [ 23 , 24 ] such as truxenones [ 25 , 26 , 27 ], or triazatruxenes [ 28 , 29 ] (e.g., D, Figure 1 ), which exhibit outstanding photophysical properties [ 30 , 31 , 32 , 33 ].…”