Four novel intensively blue luminescent chromophores were readily synthesized by bromine-lithium exchange borylation-Suzuki (BLEBS) sequence in moderate to good yields. Their electronic properties were studied by absorption and emission spectroscopy and quantum chemical calculations revealing deep-blue emission in solution as well as in the solid state and upon embedding into a PMMA (polymethylmethacrylate) matrix with small FWHM (full width at half maximum) values and CIE y values smaller than 0.1. Moreover, high photoluminescence quantum yields (PLQY), partially close to unity, are found.
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 %.
The Front Cover illustrates the structure of a highly blue luminescent emitter lighting up dark space. The electronic structure of this compound reveals emission from a balanced hybridized local and charge‐transfer (HLCT) excited state as shown by multi‐reference quantum chemical calculations. The emitter was implemented by vacuum deposition in an OLED device that exhibits an EQE (external quantum efficiency) of 2%. More information can be found in the Research Article by Thomas J. J. Müller and co‐workers.
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