The absorption and emission characteristics of (ppz)2(dipy)IrIII, (ppz)(dipy)PtII and (ppz)(dipy)PdII, where ppz stands for a phenylpyrazole and dipy for a phenyl meso-substituted dipyrrin ligand, have been investigated by theory and experiment.
Quantum chemical studies employing combined density functional and multireference configuration interaction methods suggest five excited electronic states to be involved in the prompt and delayed fluorescence emission of TpAT-tFFO. Three...
Emitters for organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) require small singlet (S1)‐triplet (T1) energy gaps as well as fast intersystem crossing (ISC) transitions. These transitions can be mediated by vibronic mixing with higher excited states Sn and Tn (n=2, 3, 4, …). For a prototypical TADF emitter consisting of a triarylamine and a dicyanobenzene moiety (TAA‐DCN) it is shown that these higher states can be located energetically by time‐resolved near‐infrared (NIR) spectroscopy.
What prompted you to investigate this topic?The relevance of electronic excitation reaches from photobiology to molecular electronics, such as organic light emitting diodes (OLEDs). We are interested in studying intersystem crossing (ISC) in molecules and in the modulation of ISC by variation of the chemical structure and of the molecular environment. Therefore, we synthesize novel diphenylamino terphenyl emitters with increased distance between donor and acceptor moieties to study their electronic properties collaboratively within the research training group RTG 2482.
What is the most significant result of this study?The designed fluorophore shows high solubility and intense blue to yellow emission in solution revealing photoluminescence quantum yields close to unity. Multi-reference quantum chemical calculations indicate a balanced hybridized local and charge-transfer excited state. Furthermore, the calculations reveal the strong involvement of the ligating p-phenylene
In this work, we perform an in‐depth investigation of the optoelectronic properties of a blue emitter (4’’‐(diphenylamino)‐2’’‐methyl‐[1,1’:4’,1’’‐terphenyl]‐4‐carbonitrile), which was reported earlier. Lippert–Mataga analysis of the emission spectra obtained in solvents of varying polarity reveal charge transfer (CT) contributions to the first singlet excited state, S1. Multi‐reference quantum chemical calculations clearly show a balanced local excitation (LE) and CT character of the S1 state and suggests the presence of a LE triplet state, T2, in its energetic vicinity. Finally, organic light emitting diodes (OLED) revealed blue emission at 451 nm and an external quantum efficiency (EQE) of 2 %, corresponding to an internal quantum efficiency (IQE) of circa 10 %.
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