New paper: Interplay of Fluorescence and Phosphorescence in Organic Biluminescent Emitters

In our recent publication entitled ‘Interplay of Fluorescence and Phosphorescence in Organic Biluminescent Emitters‘ published in the Journal of Physical Chemistry C, we discuss how the population of triplet excitons in emitters which sport efficient phosphorescence at room temperature influence the overall luminescence properties. An important emphasis here is on the exciton dynamics of the fast fluorescence (nanoseconds) and the slow phosphorescence (milliseconds), which span over six orders of magnitude in excited state lifetimes, depending on the respective sample composition. All of these results are obtained at room temperature.

We acknowledge the funding from the German excellence cluster cfaed (TU Dresden) and from European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 679213).


DPG Frühjahrstagung Dresden 2017 starts tomorrow

The DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) will take place from March 19 – 24 in Dresden this year. Below, you find a list of our group’s contributions throughout the week. We are looking forward to an exciting and fruitful week of discussions and exchange. See you there. (There is even a hashtag for the event: #DPGDD17)

Mo, 11:00 CPP 7.1 Two-color warm white hybrid OLEDs from thermally activated delayed fluorescence — Ludwig Popp, Paul Kleine, Reinhard Scholz, Ramunas Lygaitis, Olaf Zeika, Axel Fischer, Simone Lenk, and Sebastian Reineke
Mo, 11:15 CPP 7.2 Conjugation induced thermally activated delayed fluorescence — Paul Kleine, Qiang Wei, Yevhen Karpov, Xianping Qiu, Hartmut Komber, Karin Sahre, Anton Kiriy, Ramunas Lygaitis, Simone Lenk, Brigitte Voit, and Sebastian Reineke
Mo, 12:15 CPP 7.6 Ultrathin metal electrode for bottom-emitting OLEDs on buckled substrates — Yungui Li, Toni Bärschneider, Paul-Anton Will, Yuan Liu, Simone Lenk, and Sebastian Reineke
Di, 15:45 CPP 26.8 Absolute optical sensor based on biluminescence — Caterin Salas Redondo and Sebastian Reineke
Mi, 18:30 CPP 50.13 controlling excitons in exciplex host systems for efficient white OLEDs — Yuan Liu, Simone Lenk, Karl Leo, and Sebastian Reineke
Mi, 18:30 CPP 50.19 Synthesis and characterisation of the new emitters for OLED applications — Ramunas Lygaitis, Olaf Zeika, Reinhard Scholz, Ludwig Popp, Paul Kleine, Simone Lenk, and Sebastian Reineke
Mi, 13:00 DS 29.14 Influence of radiative efficiency and dipole orientation on optimal layer thicknesses of monochrome OLEDs for maximum EQE — Paul-Anton Will, Cornelius Fuchs, Reinhard Scholz, Simone Lenk, and Sebastian Reineke
Mi, 15:15 DS 34.2 Determination of the molecular orientation in absorptive organic thin films — Christian Hänisch, Simone Lenk, and Sebastian Reineke
Mi, 09:30 HL 52.1 Full Range Electrothermal Modeling of Organic Light-emitting Diodes — Axel Fischer, Koen Vandewal, Simone Lenk, and Sebastian Reineke
Mi, 15:00 HL 64.19 Diffuse Transmission and Reflection of Light Scattering Polymer Substrates for Organic Light-emitting Diodes — Pen Yiao Ang, Georg Marks, Abdalla Mahmoud, Axel Fischer, Simone Lenk, and Sebastian Reineke

Ryutaro Komatsu (see below) is currently visiting our group as part of an ongoing exchange program between TU Dresden and Universities from Japan. He is a PhD candidate of Prof. Junji Kido from Yamagata University – good chance to see some of their recent work.

Mi, 18:30 CPP 50.14 Efficient Deep-blue Pyridimidine-based TADF Emitters Using a Highly Twisted Molecular Skeleton — •Ryutaro Komatsu, Tatsuya Ohsawa, Hisahiro Sasabe, Kohei Nakao, Yuya Hayasaka, and Junji Kido


Session Preview: EP1.1 – Organic Light-Emitting Devices

Tomorrow, Tuesday March 29, we start out with the first Session of our Symposium EP1 Organic Excitonic Systems and Devices. The session runs under the title Organic Light-Emitting Devices (OLEDs). So clearly, we are looking to a collection of recent progress on the OLED technology, where the optimization of efficiency is in the central focus. Here are some keywords that will represent the content of tomorrow:

  • Enhanced emission of OLEDs
  • Bright NIR OLEDs based on high mobility polymers
  • Intrinsic degradation mechanisms in UV and blue OLEDs
  • Increased stability of TADF OLEDs
  • 100% triplet harvesting in fluorescent OLEDs
  • Blue phosphorescent OLEDs
  • Absence of triplet up-conversion in anthracene based emitters
  • Afterglow OLEDs (a demonstration of biluminescence in OLEDs)
  • Origin and control of emitter orientation in OLEDs

Our invited speakers for this session are: Mark Thompson, Stephen R. Forrest, and Jang-Joo Kim.


ERC Starting Grant awarded – Project BILUM

Exciting news: The ERC has just announced the 291 young researchers, who were awarded a 2015 ERC Starting Grant, where one funding slot was reserved for my proposal. The project is called BILUM and runs under the title ‘Novel applications based on organic biluminescence’. The project will start with April 2016 and will last for 5 years; the host institution is the Technische Universität Dresden.

The project is all about the investigation and utilization of a recently discovered phenomena called biluminescence, which is unique to organic molecules. In these molecules, two differently excited states can be formed giving rise to completely different emission properties. The key here is that both states can emit photons efficiently, typically with different color, turning these molecules into dual-state emitters – hence: biluminophores.

BILUM Scheme

BILUM has many objectives that span from fundamental research to the quest to discover novel applications. Especially, we are interested in:

    • the structure-property relationships that lead to efficient biluminescence,
    • the exciton dynamics of these dual state emitter systems,
    • the photo-stability of such compounds,
    • the compatibility of biluminophores with known processing techniques (solution and vacuum processing),
    • the quantum chemical and synthetic pathways to novel biluminophores with improved performance,
    • excitonic and photonic concepts that make use of the unique spectral and temporal characteristics of biluminescence,
    • the ratio between fluorescence and phosphorescence and ways to alter it,
    • and many more…

The project abstract reads:

Organic semiconducting molecules often make for very good luminescent materials. Fundamental excitations are localized on single molecules, which is in stark contrast to inorganic semiconductors, such that exchange interactions lead to energetically distinct singlet and triplet states. The singlet-excited state is the origin of conventional fluorescence. However, once an excitation is in the molecular triplet state, emission of photons is very unlikely, because spin conservation needs to be broken. Here, non-radiative recombination outcompetes the radiative. Recent research efforts led to the discovery of highly efficient biluminescence. Here, in addition to the fluorescence from the singlet state, the phosphorescence (triplet state emission) is unlocked by suppression of non-radiative channels at room temperature. The dynamics of both states is vastly different with nanosecond fluorescence and millisecond phosphorescence. If both channels are highly luminescent, then there is no room for loss channels. Within BILUM, the virtually unexplored phenomenon of biluminescence will be the central point: On the basic science side, efforts will be focused on the detailed understanding of structure-property relationships that are key for efficient dual state emission. At the same time, with a curiosity driven engineering approach, known bilumophores will be carefully tested in different scenarios to set the ground for future applications. Biluminescence has the potential to access non-radiative triplet states that are in many cases system limiting, to serve as ultra-broadband emitters, to introduce persistent (ultra long-lived) emission, to store photonic energy, and to allow optical sensing with internal reference emission – all on the molecular level. New bilumophores will be identified through systematic screening that will employ quantum chemical calculations and developed through organic synthesis.

For the interested reader, here are some links to our recent research publications on the matter:

– C. Salas Redondo and S. Reineke, ‘Simultaneous fluorescence and phosphorescence from organic molecules‘, SPIE newsroom (2015). DOI

– S. Reineke and M. A. Baldo, Sci. Rep. 4; DOI: 10.1038/srep03797 (2014). DOI

– S. Reineke, N. Seidler, S. R. Yost, F. Prins, W. A. Tisdale, and M. A. Baldo, Appl. Phys. Lett. 103, 093302 (2013). DOI

Below, find a short video that demonstrates the biluminescence of one example molecule at room temperature. You see a solid sample (thin film) at room temperature that is repetitively excited with a UV flashlight. Whenever the excitation source is turned off, the persistent phosphorescence remains as afterglow.

Only 5 more days until MRS Spring 2016 end of abstract submission

Just a brief reminder: The deadline for the abstract submission of the MRS Spring 2016 Meeting in Phoenix is approaching. It will close on October 15, 2016 (11:59 p.m. ET). If you are interested in organics, excitonics, systems, devices, etc., we would be happy if you consider our Symposium EP1: Organic Excitonic Systems and Devices. Please find the Call for Papers here. We have a great line-up if invited speakers covering broadly many exciting topics.

SPIE newsroom: ‘Simultaneous fluorescence and phosphorescence from organic molecules’

When all non-radiative channels of deactivation are effectively shut off, organic molecules turn into dual state emitters, giving rise to biluminescence. Here, only the effective mixing via intersystem crossing (ISC) and reverse ISC determine, which overall emission spectrum the molecules have. In an highlight article for the SPIE newsroom, Caterin Salas Redondo and I summarize what it takes to qualify as an efficient biluminophore.

Biluminescence featured in ‘Advances in Engineering’

Our work on highly efficient biluminescent organic emitters at room temperature is featured in Advances in Engineering. Find the appropriate direct link here. The work describes an organic molecule, namely (BzP)PB that shows highly efficient fluorescence and phosphorescence at room temperature. Here, the intermixing between singlet and triplet manifold only determines the relative shares of fluorescence and phosphorescence, turning this emitter into a dual state emitter, where intercombination from one spin manifold to another does not represent an internal loss channel.