Singlet harvesting with brightly emitting Cu(I) and metal-free organic compounds

Yersin, Hartmut; Czerwieniec, Rafał; Hupfer, A.

doi:10.1117/12.921372

Cited by 36 publications

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“…Therefore, this mechanism is termed "singlet harvesting". 5,6,24,25 The problem of the molecular flattening upon electronic excitation is addressed by the use of ligands with high steric demands. For instance, sterically demanding groups on the 2 and 9 positions of 1,10-phenanthroline can effectively hamper the flattening tendency in homo-and heteroleptic diimine Cu(I) complexes.…”

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“…2, can be interpreted in terms of a three state kinetic model involving the electronic ground state S 0 , the lowest triplet state T 1 , and the singlet state S 1 . Under the assumption of a fast thermalization between the T 1 and S 1 states (assuming temperature-independent decay rates), the decay time at a given temperature can be expressed by 5,6,24,25 τðTÞ…”

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“…Accordingly, a thermally activated delayed S 1 → S 0 fluorescence 22 (TADF; compare also ref. 5,6, 13,[21][22][23][24][25] occurs and the overall emission decay time becomes much shorter than that of the T 1 → S 0 phosphorescence. With respect to electroluminescent applications, this mechanism can thus also be used to harvest all triplet and singlet excitons for light generation, though in the excited † Electronic supplementary information (ESI) available: X-ray crystallographic data files (CIF), instrumentation, experimental procedures, synthesis details, crystal structures of [Cu(dmp)(R p -phanephos)](PF 6 ) and [Cu(dmp)(S p -phanephos)] (PF 6 ), lowest electronic transitions according to TD-DFT calculations, and estimation of the radiative decay rate of the S 1 → S 0 electronic transition ( prompt fluorescence) from an analysis of the absorption spectrum.…”

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Highly efficient thermally activated fluorescence of a new rigid Cu(i) complex [Cu(dmp)(phanephos)]+

2013

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The rigid [Cu(dmp)( phanephos)] + complex displays a high luminescence quantum yield of 80% at ambient temperature. In contrast to the long-lived phosphorescence of 240 µs at T < 120 K with a radiative rate of k r = 3 × 10 3 s −1 , the ambient-temperature emission represents a thermally activated delayed fluorescence (DF) with a decay time of only 14 μs and a radiative rate of k r (DF) = 6 × 10 4 s −1 . Evidence for the involvement of the excited singlet state in the emission process is presented. This material has high potential to be applied in efficient OLEDs taking advantage of the singlet harvesting mechanism.In the past decade, substantial investigations were carried out to develop novel materials for organic light emitting diodes (OLEDs), 1 in particular, to increase the device efficiency. In this respect, luminescent materials and excitation mechanisms play a crucial role. A breakthrough was reached by applying organometallic complexes based on the 3rd-row transition metals iridium and platinum. 2-6 These substances frequently display high phosphorescence quantum yields approaching even 100% and short emission decay times of a few μs. 7 Of special importance is the fact that by an electroluminescent excitation all triplet and singlet excitons formed in the emissive layer of an OLED can be utilized for light generation, whereby the emission stems from the lowest triplet state. This mechanism, representing the triplet harvesting effect, 8,9 is based on the properties of the organometallic compounds. It allows one to achieve much higher OLED efficiencies than obtainable with typical organic fluorescent (singlet) emitters by which only 25% of the total number of excitons can be exploited. However, the triplet emitters are based on high-cost platinum group metals. Therefore, alternative materials, such as Cu(I) complexes, 5,6,10-14 came into the focus of research. At first sight, Cu(I) complexes seem to exhibit substantial problems with regard to OLED applications: (1) compared to Ir or Pt, Cu as a 1st row transition metal induces much weaker spin-orbit coupling.15 As a consequence, transitions between the excited triplet state and the singlet ground state are largely forbidden. Thus, long phosphorescence decay times of several 100 μs are found. 5,6 Therefore, in an OLED, strong saturation effects would result. (2) Cu(I) complexes with reducible ligands, i.e. with energetically low-lying π* orbitals, such as aromatic diimines, often display distinct low-energy metal-toligand charge-transfer (MLCT) transitions in the visible part of the spectrum. With this type of electronic excitation, a flattening distortion of the molecular structure takes place.13a, [16][17][18] Such structural rearrangements are usually connected with an increase of non-radiative deactivation or even quenching of the emission due to an increase of the Franck-Condon factors that couple the excited state and the ground state. 19,20 This is especially distinct in non-rigid environments. 21This contribution presents a new, adequately designe...

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Highly efficient thermally activated fluorescence of a new rigid Cu(i) complex [Cu(dmp)(phanephos)]+

2013

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“…Compared with normal fluorescence, where the excited-state lifetime is in the order of ns, the excited-state lifetime is longer, often in the order of μs or more-the term TADF accounts for these observations. Occasionally, the term singlet harvesting [14][15][16]46 is used, because all excitons are harvested via the singlet state S 1 . 13 A typical TADF emitter is tetrakis-N-carbazoyl-isophthalonitrile (4CzIPN; Fig.…”

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Review of organic light-emitting diodes with thermally activated delayed fluorescence emitters for energy-efficient sustainable light sources and displays

Volz

2016

J. Photon. Energy

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Daniel Volz, "Review of organic light-emitting diodes with thermally activated delayed fluorescence emitters for energy-efficient sustainable light sources and displays," J. Photon. Energy 6(2), 020901 (), doi: 10.1117/1.JPE.6.020901. Abstract. Thermally activated delayed fluorescence (TADF) is an emerging hot topic. Even though this photophysical mechanism itself has been described more than 50 years ago and optoelectronic devices with organic matter have been studied, improved, and even commercialized for decades now, the realization of the potential of TADF organic light-emitting diodes (OLEDs) happened only recently. TADF has been proven to be an attractive and very efficient alternative for phosphorescent materials, such as dopants in OLEDs, light-emitting electrochemical cells as well as potent emitters for chemiluminescence. In this review, the TADF concept is introduced in terms that are also understandable for nonchemists. The basic concepts behind this mechanism as well as state-of-the-art examples are discussed. In addition, the future economic impact, especially for the lighting and display market, is addressed here. We conclude that TADF materials are especially helpful to realize efficient, durable deep blue and white displays.

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TADF Material Design: Photophysical Background and Case Studies Focusing on Cu(I) and Ag(I) Complexes^a

Yersin

Czerwieniec

Shafikov

et al. 2018

Highly Efficient OLEDs

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Singlet harvesting with brightly emitting Cu(I) and metal-free organic compounds

Cited by 36 publications

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Highly efficient thermally activated fluorescence of a new rigid Cu(i) complex [Cu(dmp)(phanephos)]+

Highly efficient thermally activated fluorescence of a new rigid Cu(i) complex [Cu(dmp)(phanephos)]+

Review of organic light-emitting diodes with thermally activated delayed fluorescence emitters for energy-efficient sustainable light sources and displays

TADF Material Design: Photophysical Background and Case Studies Focusing on Cu(I) and Ag(I) Complexes^a

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Singlet harvesting with brightly emitting Cu(I) and metal-free organic compounds

Cited by 36 publications

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Highly efficient thermally activated fluorescence of a new rigid Cu(i) complex [Cu(dmp)(phanephos)]+

Highly efficient thermally activated fluorescence of a new rigid Cu(i) complex [Cu(dmp)(phanephos)]+

Review of organic light-emitting diodes with thermally activated delayed fluorescence emitters for energy-efficient sustainable light sources and displays

TADF Material Design: Photophysical Background and Case Studies Focusing on Cu(I) and Ag(I) Complexesa

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TADF Material Design: Photophysical Background and Case Studies Focusing on Cu(I) and Ag(I) Complexes^a