Our next manuscript was accepted in Chemistry – A Europan Journal
Star-Shaped Conjugated Molecules with Oxa- or Thiadiazole Bithiophene Side Arms.
Star-shaped conjugated molecules, consisting of a benzene central unit symmetrically trisubstituted with either oxa- or thiadiazole bithiophene groups, were synthesized as promising molecules and building blocks for application in (opto)electronics and electrochromic devices. Their optical (Eg(opt)) as well as electrochemical (Eg(electro)) band gaps depended on the type of the side arm and the number of solubilizing alkyl substituents. Oxadiazole derivatives showed Eg(opt) slightly below 3 eV and by 0.2 eV larger than those determined for thiadiazole-based compounds. The presence of alkyl substituents in the arms additionally lowered the band gap. The obtained compounds were efficient electroluminophores in guest/host-type light-emitting diodes. They also showed a strong tendency to self-organize in monolayers deposited on graphite, as evidenced by scanning tunneling microscopy. The structural studies by X-ray scattering revealed the formation of supramolecular columnar stacks in which the molecules were organized. Differences in macroscopic alignment in the specimen indicated variations in the self-assembly mechanism between the molecules. The compounds as trifunctional monomers were electrochemically polymerized to yield the corresponding polymer network. As shown by UV/Vis-NIR spectroelectrochemical studies, these networks exhibited reversible electrochromic behavior both in the oxidation and in the reduction modes.
Kamil Kotwica, Anastasia Kostyuchenko, Przemyslaw Data, Tomasz Marszalek, Lukasz Skorka, Tomasz Jaroch, Sylwia Kacka, Malgorzata Zakorska, Robert Nowakowski, Andrew Monkman, Alexander Fisyuk, Wojciech Pisula, Adam Pron.
Our next manuscript was accepted in Advanced Science
The Role of Local Triplet Excited States and D-A Relative Orientation in Thermally Activated Delayed Fluorescence: Photophysics and Devices
Here, a comprehensive photophysical investigation of a the emitter molecule DPTZ-DBTO2, showing thermally activated delayed fluorescence (TADF), with near-orthogonal electron donor (D) and acceptor (A) units is reported. It is shown that DPTZ-DBTO2 has minimal singlet–triplet energy splitting due to its near-rigid molecular geometry. However, the electronic coupling between the local triplet (3LE) and the charge transfer states, singlet and triplet, (1CT, 3CT), and the effect of dynamic rocking of the D–A units about the orthogonal geometry are crucial for efficient TADF to be achieved. In solvents with low polarity, the guest emissive singlet 1CT state couples directly to the near-degenerate 3LE, efficiently harvesting the triplet states by a spin orbit coupling charge transfer mechanism (SOCT). However, in solvents with higher polarity the emissive CT state in DPTZ-DBTO2 shifts below (the static) 3LE, leading to decreased TADF efficiencies. The relatively large energy difference between the 1CT and 3LE states and the extremely low efficiency of the 1CT to 3CT hyperfine coupling is responsible for the reduction in TADF efficiency. Both the electronic coupling between 1CT and 3LE, and the (dynamic) orientation of the D–A units are thus critical elements that dictate reverse intersystem crossing processes and thus high efficiency in TADF.
Fernando Dias, Jose Santos, David Graves, Przemyslaw Data, Roberto Noboyasu, Mark Fox, Andrei Batsanov, Tiago Palmeira, Mario Berberan-Santos, Martin Bryce, Andrew Monkman.
XIXth International Krutyn Summer School, Krutyn (Poland) – 15-21.05.2016
This XIXth International Krutyn Summer School – „Aggregation-Induced Emission (AIE): Phenomenon, Principle and Application”- is organized by the Institute of Physical Chemistry of the Polish Academy of Sciences, Poland, The Hong Kong University of Science & Technology, and The South China University of Technology. This Summer School aims at the state-of-the-art training in the form of lectures and consulting sessions designed for Ph.D. students and young researchers seeking to reinforce their knowledge and skills in the field of advanced photonic materials. The school is intended both for people already active in this R&D field, as well as for those new to the field.
P. Data, P. Pander
Our next manuscript was accepted in Chemistry – A Europan Journal
Soluble Flavanthrone Derivatives: Synthesis, Characterization, and Application to Organic Light-Emitting Diodes.
Simple modification of benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine-8,16-dione, an old and almost-forgotten vat dye, by reduction of its carbonyl groups and subsequent O-alkylation, yields solution-processable, electroactive, conjugated compounds of the periazaacene type, suitable for the use in organic electronics. Their electrochemically determined ionization potential and electron affinity of about 5.2 and -3.2 eV, respectively, are essentially independent of the length of the alkoxyl substituent and in good agreement with DFT calculations. The crystal structure of 8,16-dioctyloxybenzo[h]benz[5,6] cridino[2,1,9,8-klmna]acridine (FC-8), the most promising compound, was solved. It crystallizes in space group P (1) over bar and forms pi-stacked columns held together in the 3D structure by dispersion forces, mainly between interdigitated alkyl chains. Molecules of FC-8 have a strong tendency to self-organize in monolayers deposited on a highly oriented pyrolytic graphite surface, as observed by STM. 8,16-Dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines are highly luminescent, and all have photoluminescence quantum yields of about 80%. They show efficient electroluminescence, and can be used as guest molecules with a 4,4′-bis(N-carbazolyl)-1,1′-biphenyl host in guest/host-type organic light-emitting diodes. The best fabricated diodes showed a luminance of about 1900 cdm(-12), a luminance efficiency of about 3 cdA(-1), and external quantum efficiencies exceeding 0.9 %.
Kamil Kotwica, Piotr Bujak, Przemyslaw Data, Wojciech Krzywiec, Damian Wamil, Piotr Gunka, Lukasz Skorka, Tomasz Jaroch, Robert Nowakowski, Adam Pron, Andrew Monkman.
4th Workshop on Organic Electronics and Nanophotonics, WOREN2016, Aussois (France) – 20-25.03.2016
The acronym WOREN was derived from the full name of the conference: „Workshop on Organic Electronics and Nanophotonics”. WOREN provides an interdisciplinary forum for scientists working in the field of molecular and polymeric materials with emphasis on new phenomena in electronics and nanophotonics. The topics covered by subjected contributions are related to phenomena, materials and devices related to structures consisting of thin (submicron) layers of organic materials.
P. Data, R. Motyka, P. Pander
Our next manuscript was accepted in Angewandte Chemie
Dibenzo[a,j]phenazine-Cored Donor-Acceptor-Donor (D-A-D) Compounds as New Efficient Green to Red/NIR Thermally Activated Delayed Fluorescence (TADF) OLED Emitters
A new family of TADF emitters based on U-shaped D-A-D architecture with a novel accepting unit has been developed. All investigated compounds have small singlet-triplet energy splitting (DEST) ranging from 0.02 to 0.20 eV and showed efficient TADF properties. The lowest triplet state of the acceptor unit plays the key role in the TADF mechanism. OLEDs fabricated with these TADF emitters achieved excellent efficiencies up to 16% EQE.
Przemyslaw Data, Piotr Pander, Masato Okazaki, Youhei Takeda, Satoshi Minakata, Andrew Monkman.
Our next manuscript was accepted in Journal of Materials Chemistry C
The key to engineering an efficient TADF emitter is to achieve a small energy splitting between a pair of molecular singlet and triplet states. This work makes important contributions towards achieving this goal. By studying the new TADF emitter 2,7-bis(phenoxazin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DPO-TXO2) and the donor and acceptor units separately, the available radiative and non-radiative pathways of DPO-TXO2 have been identified. The energy splitting between singlet and triplet states was clearly identified in four different environments, in solutions and solid state. The results show that DPO-TXO2 is a promising TADF emitter, having ΔEST = 0.01 eV in zeonex matrix. We further show how the environment plays a key role in the fine tuning of the energy levels of the 1CT state with respect to the donor 3LED triplet state, which can then be used to control the ΔEST energy value. We elucidate the TADF mechanism dynamics when the 1CT state is located below the 3LE triplet state which it spin orbit couples to, and we also discuss the OLED device performance with this new emitter, which shows maximum external quantum efficiency (E.Q.E.) of 13.5% at 166 cd m−2.
Paloma Santos*, Jonathan Ward, Przemyslaw Data, Andrei Batsanov, Martin Bryce, Fernando Dias, Andrew Monkman.
Our third manuscript was accepted in the Journal of Physical Chemistry C
Organic electronics, mainly due to advancements in OLED (Organic Light Emitting Diode) technology, is a fast developing research area having already revolutionized the displays market. This direction presents the use of exciplex emitters and thermally activated delayed fluorescence (TADF) in OLEDs, to give efficient, stable emitters that do not use scarce and expensive materials such as iridium. Here, it is shown for the first time several diketopyrrolopyrrole (DPP) derivatives that could be used as emitters in OLED devices. We were able to improve the of efficiency DPP materials by forming exciplex enhanced OLED devices. These organic materials were also characterized by electrochemical and spectroscopic methods in order to elucidate each molecule’s interaction and decreasing the photoluminescence efficiency.
Przemyslaw Data*, Aleksandra Kurowska, Sandra Pluczyk, Pawel Zassowski, Piotr Pander, Rafal Jedrysiak, Michal Czwartosz, Lukasz Otulakowski, Jerzy Suwinski, Mieczyslaw Lapkowski, Andrew Monkman.
Our second manuscript was accepted in Advanced Optical Materials
Rational design of TADF polymers using a donor–acceptor monomer with enhanced TADF efficiency induced by the energy alignment of charge transfer and local triplet excited states.
The photophysics of thermally activated delayed fluorescence (TADF) in phenothiazine-dibenzothiophene-S,S-dioxide (PTZ-DBTO2) molecule is investigated in detail. First, it is shown that the proximity of local triplet excited states (3LE), e.g., 3D or 3A, above or below the DA charge transfer states (CT) is crucial for the efficiency of the TADF mechanism in PTZ-DBTO2. This TADF emitter is then used as a monomer unit to design polymer materials with efficient TADF. The reverse intersystem crossing mechanism (RISC) that supports TADF is able to compete with internal conversion and triplet–triplet annihilation (TTA) in the polymer chains and generates efficient TADF emission in the polymer pristine films. Prototype devices with PTZ-DBTO2 dispersed in 4,4′-bis(N-carbazolyl)-2,2′-biphenyl (CBP) host give excellent performance with EQE of ≈22% at low luminance (<100 cd m−2), for 100 cd m−2 the EQE is 19.4%. In the case of solution processed devices, using the novel TADF polymers, the performance is much lower, EQE ≈3.5% at 100 cd m−2, which is still the highest value for a polymer TADF system at useful brightness, yet reported. This results from a combination of weak charge transport properties in these materials and device fabrication methods that require further improvement. Nevertheless, these results pave the way to explore TADF in polymer light emitting diodes (PLEDs), using less costly deposition methods, such as spin-coating and inkjet printing, which are more appropriate for large area deposition.
Roberto Nobuyasu, Zhongjie Ren, Gareth Gryffiths, Andrei Batsanov, Przemyslaw Data, Andrew Monkman, Martin Bryce, Shouke Yan, Fernando Dias.
Our first manuscript was accepted in Chemistry Communications
The interplay of thermally activated delayed fluorescence (TADF) and room temperature organic phosphorescence in sterically-constrained donor–acceptor charge-transfer molecules.
A series of phenothiazine–dibenzothiophene-S,S-dioxide charge-transfer molecules have been synthesized. Increasing steric restriction around the donor–acceptor bond significantly alters contributions from TADF and phosphorescence. Bulky substituents on the 1-(and 9) position(s) of the phenothiazine result in no TADF in the solid state; instead strong phosphorescence is observed at ambient temperature.
Jonathan Ward, Roberto Nobuyasu, Andrei Batsanov, Przemyslaw Data, Andrew Monkman, Fernando Dias, Martin Bryce.*