Yersin, Hartmut and Czerwieniec, Rafal and Shafikov, Marsel Z. and Suleymanova, Alfiya F. (2017) TADF Material Design: Photophysical Background and Case Studies Focusing on Cu-I and Ag-I Complexes. WILEY-V C H VERLAG GMBH, WEINHEIM.
Full text not available from this repository. (Request a copy)Abstract
The development of organic light emitting diodes (OLEDs) and the use of emitting molecules have strongly stimulated scientific research of emitting compounds. In particular, for OLEDs it is required to harvest all singlet and triplet excitons that are generated in the emission layer. This can be achieved using the so-called triplet harvesting mechanism. However, the materials to be applied are based on high-cost rare metals and therefore, it has been proposed already more than one decade ago by our group to use the effect of thermally activated delayed fluorescence (TADF) to harvest all generated excitons in the lowest excited singlet state S-1. In this situation, the resulting emission is an S1S0 fluorescence, though a delayed one. Hence, this mechanism represents the singlet harvesting mechanism. Using this effect, high-cost and strong SOC-carrying rare metals are not required. This mechanism can very effectively be realized by use of Cu-I or Ag-I complexes and even by purely organic molecules. In this investigation, we focus on photoluminescence properties and on crucial requirements for designing Cu-I and Ag-I materials that exhibit short TADF decay times at high emission quantum yields. The decay times should be as short as possible to minimize non-radiative quenching and, in particular, chemical reactions that frequently occur in the excited state. Thus, a short TADF decay time can strongly increase the material's long-term stability. Here, we study crucial parameters and analyze their impact on the TADF decay time. For example, the energy separation E(S-1-T-1) between the lowest excited singlet state S-1 and the triplet state T-1 should be small. Accordingly, we present detailed photophysical properties of two case-study materials designed to exhibit a large E(S-1-T-1) value of 1000cm(-1) (120meV) and, for comparison, a small one of 370cm(-1) (46meV). From these studiesextended by investigations of many other Cu-I TADF compoundswe can conclude that just small E(S-1-T-1) is not a sufficient requirement for short TADF decay times. High allowedness of the transition from the emitting S-1 state to the electronic ground state S-0, expressed by the radiative rate k(r)(S1S0) or the oscillator strength f(S1S0), is also very important. However, mostly small E(S-1-T-1) is related to small k(r)(S1S0). This relation results from an experimental investigation of a large number of Cu-I complexes and basic quantum mechanical considerations. As a consequence, a reduction of (TADF) to below a few s might be problematic. However, new materials can be designed for which this disadvantage is not prevailing. A new TADF compound, Ag(dbp)(P-2-nCB) (with dbp=2,9-di-n-butyl-1,10-phenanthroline and P-2-nCB=bis-(diphenylphosphine)-nido-carborane) seems to represent such an example. Accordingly, this material shows TADF record properties, such as short TADF decay time at high emission quantum yield. These properties are based (i)on geometry optimizations of the Ag-I complex for a fast radiative S1S0 rate and (ii)on restricting the extent of geometry reorganizations after excitation for reducing non-radiative relaxation and emission quenching. Indeed, we could design a TADF material with breakthrough properties showing (TADF)=1.4s at 100% emission quantum yield.
| Item Type: | Other |
|---|---|
| Uncontrolled Keywords: | LIGHT-EMITTING-DIODES; ACTIVATED DELAYED FLUORESCENCE; CYCLOMETALATED IRIDIUM COMPLEXES; LIGAND CHARGE-TRANSFER; 3-COORDINATE COPPER(I) COMPLEXES; TRANSFER RADICAL-ADDITION; TRIPLET-SINGLET EMISSION; EXCITED-STATE PROPERTIES; TIME-RESOLVED SPECTRA; ELECTROCHEMICAL-CELLS; copper(I) complexes; high fluorescence rates; silver(I) complexes; singlet harvesting; thermally activated delayed fluorescence |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Chemistry III - Physical Chemistry (Molecular Spectroscopy and Photochemistry) > Prof. Dr. Hartmut Yersin |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 14 Dec 2018 13:18 |
| Last Modified: | 11 Feb 2019 14:47 |
| URI: | https://pred.uni-regensburg.de/id/eprint/1684 |
Actions (login required)
 |
View Item |
