Thermally Activated Delayed Fluorescence and Phosphorescence Quenching in Iminophosphonamide Copper and Zinc Complexes. Issue 61 (1st June 2021)

• Record Type: Journal Article
• Authors: Goswami, Bhupendra; Feuerstein, Thomas J.; Yadav, Ravi; Lebedkin, Sergei; Boden, Pit J.; Steiger, Sophie T.; Niedner‐Schatteburg, Gereon; Gerhards, Markus; Kappes, Manfred M.; Roesky, Peter W.
• Is Part Of: Chemistry. Volume 27:Issue 61(2021)
• Page Start: 15110
• Page End: 15119
• Publication Date: 2021-06-01
• Subjects: copper -- iminophosphonamides -- photoluminescence -- step-scan FTIR -- TADF -- zinc; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.202101247
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The synthesis of copper and zinc complexes of four variably substituted iminophosphonamide ligands is presented. While the copper complexes form ligand‐bridged dimers, the zinc compounds are monomeric. Due to different steric demand of the ligand the arrangement of the ligands within the dimeric complexes varies. Similar to the structurally related iminophosphonamide complexes of alkali metals and calcium, the steady‐state and time‐resolved photoluminescence (PL) of four of the seven compounds studied here as solids in a temperature range of 5–295 K can be described within the scheme of thermally activated delayed fluorescence (TADF). Accordingly, they exhibit bright blue‐green phosphorescence at low temperatures (<100 K), which turns into delayed fluorescence by increasing the temperature. However, unusually, the fluorescence is practically absent in two copper complexes which otherwise still conform to the TADF scheme. In these cases, the excited singlet states decay essentially non‐radiatively and their thermal population from the corresponding low‐lying triplet states efficiently quenches PL (phosphorescence). Three other copper and zinc complexes only exhibit prompt fluorescence, evidencing a wide variation of photophysical properties in this class of compounds. The excited states of the copper complex with especially pronounced phosphorescence quenching were also investigated by low‐temperature time‐resolved infrared spectroscopy and quantum chemical calculations. Abstract : To glow or not to glow : Chiral iminophosphonamide copper and zinc complexes are presented. Some steady‐state and time‐resolved photoluminescence (PL) features studied at low temperatures can be described within the thermally activated delayed fluorescence (TADF) scheme. However, unusually, the fluorescence is nearly absent in two complexes and the low‐lying triplet state quenches PL. Some excited states were further investigated by time‐resolved FTIR spectroscopy and quantum chemical calculations.