21st June – 9.40 am

Vibrational coupling in thermally-activated delayed fluorescence, how multiple resonant energy states allow you to beat Ir triplet harvesting.

Andrew MonkmanDept. of Physics, Durham University, South Road Durham, UK

Light generation by electroluminescence in the best OLEDs can have 100% internal charge to photon conversionefficiency. This requires very efficient triplet to singlet excited state harvesting, and has been the strict preserve ofelectrophosphorescent heavy metal complex emitters, until now. However, recently it has been discovered thatorganic donor-acceptor (DA) charge transfer molecules can also yield such efficient triplet harvesting and OLEDS with100% internal efficiency fabricated. Here the process of triplet harvesting is by thermally-activated delayedfluorescence, ‘TADF’, i.e. E-type delayed fluorescence. From detailed photophysical measurements of intramolecularcharge transfer (ICT) states especially temperature dependent time-resolved delayed emission and photoinducedabsorption the energy levels involved in the reverse intersystem crossing mechanism were elucidated 1, and throughdetailed quantum chemical modelling, TADF fully understood. Vibronic coupling second order spin orbit interactionsdominate both ISC and reverse ISC (rISC) and we have shown how both D-A-D molecule structure and conformationcontrol TADF 2, leading on to the demonstration of deep blue OLEDs having 22.4% EQE 3. Here I will explain these mostintriguing photophysical processes 4, and describe our latest TADF emitters 5 that seem to break the laws of physics inhaving a PLQY ~1 and rISC rate > 10-7 s-1, i.e. a faster triplet harvesting rate than an Ir complex!

References1. Etherington, M. K., et al. Nature Communications 7, 13680 (2016).2. Gibson, J., Monkman, A. P. & Penfold, T.J. ChemPhysChem 17 2956 (2016).3. dos Santos, P.L. et al, J.Phys.Chem.Lett. 7, 3341 (2016).4. Dias, F. B. et al. Advanced Science 3, 1600080 (2016).5. dos Santos, P.L. et al, Advanced Science 1700989 (2018).

21st June – 10.10 am

Synthesis and characterisation of the new emitters for OLED applications

R.Lygaitis1, D. Gudeika1, O. Zeika2, R. Scholz2, P. Kleine2, L. Popp2, S. Lenk2, Juozas V. Grazulevicius1, S. Reineke2

1 Kaunas University of Technology, Lithuania2 Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden

Organic light-emitting diodes (OLEDs) are a sustainable, low cost light source used in displays and other applications. Quite big stepin progress was made when phosphorescent materials containing Ir(III), Pt(III), or other heavy metals were used in order to harvest both singletand triplet excitons by means of enhanced intersystem crossing. Today, one of the issues which prevent current iridium-based, phosphorescentemitters widely used in the lighting markets, is that iridium is the fourth rarest naturally-occurring element on the planet, so the usage of thiselement in large scales could be very risky. Therefore, new iridium-free emitters harvesting both singlet and triplet excitons are of big interest.

In this talk the synthesis and characterisation of the series of carbazole and acridane-based derivatives containing electronaccepting trifluoromethyl, cyano and sulfonyl groups which support certain intermolecular charge transfer. The newly synthesised derivativeswere characterised by means of absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, and cyclic voltammetry. Thecollected data prove that our new materials could be regarded as potential TADF emitters. As well emission properties of flat structure molecularmaterial 3,8,12-tri-tert-butyl-5H-benzo[6,7]azepine[3,2,1-de]acridin-10(6H)-none were studied choosing three different polymeric matrixmaterials: Zeonex, polymethylmethacrylate and poly(methyl methacrylate-co-ethylene glycol dimethacrylate). Poly (methyl methacrylate-co-ethylene glycol dimethacrylate) was synthesized by photo-polymerization process. Copolymer was characterized by IR spectroscopy. Roomtemperature delayed fluorescence has been observed from mixtures of 3,8,12-tri-tert-butyl-5H-benzo[6,7]azepine[3,2,1-de]acridin-10(6H)-noneand polymers.

21st June – 10.40 am

Ultrastable glass emission layers – a concept to improve phosphorescent OLEDs –

does it work for TADF?

Paul-Anton Will2, Paulius Imbasas2, Joan Ràfols-Ribé1, Christian Hänisch2, Marta González-Silveira1, Simone Lenk2, Javier

Rodríguez-Viejo1, Sebastian Reineke2

1Group of Nanomaterials and Microsystems, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain

2Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische

Universität Dresden, 01187 Dresden, Germany

Organic light-emitting diodes (OLEDs) have become on of the most promising solid state light sources. For all current and

future applications, these devices need to operate at their best performance with respect to external quantum efficiency and

device lifetime. In recent years, thermally activated delayed fluorescence (TADF) has moved into the central focus of emitter

material design, raising hope for further improved OLEDs. Recently, we have identified a processing scheme involving the

controlled heating of the substrate during layer deposition as a way to improve both efficiency and lifetime of phosphorescent

OLEDs. Here, the optimum is found when the layers are formed as ultrastable glasses, which happens slightly below the glass

transition temperature of the respective materials. We selected TPBi as a host material with comparably high Tg of 122 °C

[2,2',2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)] for four different phosphorescent emitters, i.e. one blue, two

green, and one red Ir-complexes). All devices showed improvement over the respective room temperature control devices.

This presentation will include first results on the application of this concept to TADF emitters, where both device and

photophysical data of the systems of interest are presented.

21st June – 11.35 amPhotophysics of TADF Emitters for Efficient Triplet Harvesting in OLEDs

Roberto S. Nobuyasu1, Jonathan S. Ward2, Jamie Gibson3, Thomas J Penfold3, Martin R. Bryce2, Fernando B. Dias1

1Department of Physics, Durham University, UK; 2Department of Chemistry, Durham University, UK; 3School ofChemistry, Newcastle University, UK

The electrical current used to drive organic light emitting diodes (OLEDs) creates large proportion of non-emissive tripletstates due to the localized nature of excitons in organic molecules. This gives origin to large exchange interactions andformation of excited states with spin 0 (singlet) and spin 1 (triplet) in a ratio of 1:3. A fraction of the singlet states (S1)created upon charge recombination may also be converted to triplet states (T1), due to local hyperfine interactions thataffect the initially created charge transfer state, and due to intersystem crossing (ISC) from S1 to T1, caused by spin-orbitcoupling. Therefore, triplets represent a major loss in the luminescence efficiency of OLEDs, and improving triplet harvestingto contribute to the radiative mechanism is a key process to improve device efficiency. Molecules showing thermallyactivated delayed fluorescence (TADF) have been introduced in recent years as alternative to heavy-metal complexes. TADFsare designed with electron donor (D) and electron acceptor (A) units covalently linked to produce a singlet-triplet energy gapof a few hundred meV. In these conditions, significant population of the triplet state occupies upper vibrational levels andare able to cross back to the singlet manifold due to reverse intersystem crossing (RISC). This process gives origin to delayedfluorescence. OLEDs using TADF emitters show impressive performances in the green region, sometimes with EQEs above25%. However, for emission in the blue and red regions, the performance of TADFs is weaker and further improvement isneeded. In particular, a pronounced roll-off on device efficiency is often observed at high current densities. The causes forthis loss in efficiency are still unclear, but triplet-triplet annihilation and triplet-polaron quenching processes are thought tobe the most probable causes. As the influence of these quenching mechanisms are enhanced by the long luminescencelifetime of TADF emitters, obtaining molecular structures with faster ISC/RISC rates, and thus shorter excited-state lifetimesare in high demand to resolve these drawbacks.Here, we report the investigation of D-A emitters with tailored molecular structure and conformation to promote efficientTADF emission. Here, we show that molecular geometry has profound influence on the TADF performance. Molecules withbulky side substituents in different positions of the D and A units were studied to investigate the effect of moleculargeometry on the energy of the singlet and triplet excited states and TADF efficiency. We found that the energy of the singletstate with charge transfer character (1CT) is increasingly shifted to higher energies with increasing bulkiness of thesubstituent in the D unit, i.e. bulky side groups that increasingly restrict the dynamic rotation around the DA axis stronglydestabilize the 1CT state, but when the substitution occurs in the acceptor unit the effect is much weaker. Remarkably, whenthe bulky side groups are substituted in the donor unit the TADF emission is strongly supressed. This may be due to thecumulative influence of restricted dynamic rocking around the DA axis and changes on molecular conformation andelectronic properties of the substituted molecules.

Fig.1 a) kinetic mechanism for TADF emission. b) The effect of bulky D substituents

on the TADF transients from D-A-D emitters.

Once more, the effects appears to be less prominent when the substitutionoccurs in the acceptor unit, but still the influence on the reverse intersystemcrossing mechanism and contribution of TADF to the overall emission isnoticed. We then discuss the influence of the energy alignment between localtriplet excited states (3LE) and the 1CT state on the observation of efficientTADF.1. F. B. Dias et al., Methods Appl. Fluoresc. 5, 12001 (2017). 2. F. B. Dias et al. Adv. Sci. 3, 1–10 (2016).

21st June – 12.05 am

21st June – 12.35 am

Deep Blue Organic TADF Emitters for Electroluminescent Devices

Eli Zysman-ColmanOrganic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrewswww.zysman-colman.com

The first generation OLEDs were based on organic fluorescent emitters. Their efficiency was intrinsically capped at 25% due to only being able to recruit singlet excitons. The second generation OLEDs have employed organometallic phosphorescent emitters, which harvest both singlet and triplet excitons for emission due to the enhanced intersystem crossing mediated by the heavy metals such as iridium(III) and platinum(II). These metal complexes possess very desirable optoelectronic properties and lead to very efficient OLED devices. However, the rarity of these metals, their high cost and their toxicity are important detracting features that inhibit large-scale, worldwide adoption of OLED technology, particularly for lighting where, unlike displays, low cost devices are crucial to market growth. The third generation OLEDs are based on small organic compounds emit via a thermally activated delayed fluorescence (TADF) mechanism. As with phosphorescent emitters, OLEDs using these emitters can recruit 100% of the excitons. In this presentation, we present our recent efforts towards blue emitter in electroluminescent devices

21st June – 2.30 pm

Spectroscopy Techniques for ISC quantum yield determination

João Avó1, João C. Lima2, Fernando B. Dias3, Mário N. Berberan-Santos1

1 CQFM-IN and IBB-Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal2 LAQV-REQUIMTE, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Portugal3 Department of Physics, Durham University, United Kingdom

Of the factors that determine the applicability of TADF emitters in OLED devices, rISC quantum yield (φrISC) is of utmostimportance.[1] In the absence of reliable methods for its determination, photophysicists often rely on the determination of ISCquantum yield (φISC) to measure the ability of an emitter to undergo a change in spin configuration, since the two processes areintrinsically related.[2] Over the last century, several methodologies for this quantification have been developed and, even afterdecades of technological evolution, most of them are still useful today.[3,4] In this talk, some of these methods will be overviewed,and their applicability in the photophysical characterization of TADF emitters will be discussed. The advantages and limitations of eachmethod will be highlighted through demonstration of case studies involving novel TADF emitting organic molecules.

[1] – F.B. Dias, T.J. Penfold, A.P. Monkman, Methods Appl.Fluoresc., 2017, 5, 012001[2] – T. Palmeira, M.N. Berberan-Santos, J. Phys. Chem. C, 2017, 121, 701[3] – I. Carmichael, G.L. Hug, J. Phys. Chem. Ref. Data, 1986, 15, 1[4] – B. Amand, R. Bensasson, Chem. Phys. Lett., 1975, 34, 44

21st June – 3.00 pm

Improving OLED outcoupling efficiency using oriented emitters

Caroline Murawski1, Arko Graf2, Chris Elschner3, Simone Lenk3, Sebastian Reineke3, Jana Zaumseil2, andMalte C. Gather1

Organic Semiconductor Centre, SUPA, School of Physics and Astrononomy, University of St Andrews,North Haugh, St Andrews, KY16 9SS, UKInstitute for Physical Chemistry, Universität Heidelberg, 69120 Heidelberg, GermanyDresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for AppliedPhysics, Technische Universität Dresden, Nöthnitzer Str. 61, 01187 Dresden, Germany

While the internal quantum efficiency of organic light-emitting diodes can reach up to 100%, lightoutcoupling still remains a major bottleneck, which reduces the external quantum efficiency to around25% in a standard device architecture. In order to improve light outcoupling, the use of emitters withhorizontally oriented transition dipoles bears great potential. Here, we present our recent investigationson emitter orientation in heteroleptic and homoleptic iridium compounds. Furthermore, wedemonstrate infrared OLEDs based on carbon nanotubes that provide extreme horizontal transitiondipole orientation and, thus, boost the outcoupling efficiency to 49%.

21st June – 3.30 pmReverse Intersystem Crossing in Aromatic Carbonyls – Before and After rISC2016

C. Torres Ziegenbein, K. Thom, P. Gilch

Institut für Physikalische Chemie, HHU Düsseldorf, Universitätsstr. 1, 40225 Düsseldorf, Germany

Before. Textbooks on organic photochemistry devote much space to aromatic carbonyls (see e.g. ref.1). Thesecommonly undergo efficient intersystem crossing (ISC) and the resulting triplet excitations are often precursors ofphotoproducts. Seeking deeper understanding of these ISC processes we conducted femtosecond spectroscopy on somearomatic carbonyls (xanthone (X) and thioxanthone (TX))2-5. These studies revealed that in certain solvents the primarilyexcited singlet state of TX (a 1* one) undergoes ISC in few picoseconds (see Figure, top). The ISC process populates anupper triplet state of 3n* character. This state is nearly isoenergetic with the singlet state resulting in an equilibrium ofthe two states. Surprisingly, the equilibrium persists for nanoseconds, i.e. the internal conversion to the lowest triplet(3*) is slow.

After. A corollary of this kinetic scheme is that population of the upper triplet state ought to result in fluorescenceemission. In other words, TX ought to act as a triplet harvester. During the rISC 2016 workshop the Monkman and mygroup agreed to join forces and give experimental evidence for that6. In the experiment a sensitizer (1,4-dichlorobenzene, DCB) was brought to its triplet state by photo-excitation. In a diffusion limited process it transfers itsenergy to TX (time constant ~ 100 ns). As shown by time resolved emission spectroscopy this transfer results influorescence of TX. TX indeed acts as a triplet harvester. Because of its small fluorescence quantum yield TX itself is notsuited for OLED applications. As will be outlined in the talk other aromatic carbonyls are much more promising.

1. Turro, N. J.; Ramamurthy, V.; Scaiano, J. C., Modern molecular photochemistry of organic molecules. University Science Books: Sausalito, Calif., 2010.2. Heinz, B.; Schmidt, B.; Root, C.; Satzger, H.; Milota, F.; Fierz, B.; Kiefhaber, T.; Zinth, W.; Gilch, P., Phys. Chem. Chem. Phys. 2006, 8 (29), 3432-3439.3. Wöll, D.; Laimgruber, S.; Galetskaya, M.; Smirnova, J.; Pfleiderer, W.; Heinz, B.; Gilch, P.; Steiner, U. E., J. Am. Chem. Soc. 2007, 129, 12148-12158.4. Villnow, T.; Ryseck, G.; Rai-Constapel, V.; Marian, C. M.; Gilch, P., J. Phys. Chem. A 2014, 118 (50), 11696-11707.5. Mundt, R.; Villnow, T.; Ziegenbein, C. T.; Gilch, P.; Marian, C.; Rai-Constapel, V., Phys. Chem. Chem. Phys. 2016, 18 (9), 6637-6647.6. Torres Ziegenbein, C.; Fröbel, S.; Glöß, M.; Nobuyasu, R. S.; Data, P.; Monkman, A.; Gilch, P., ChemPhysChem 2017, 18 (17), 2314–2317.

22nd June – 8.30 am

The Theory of Molecules Exhibiting Thermally Activated Delayed Fluorescence

Thomas J Penfold*

*Chemistry-School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.E-mail: tom.penfold@ncl.ac.uk

Thermally Activated Delayed Fluorescence (TADF) has become a core focus for the development of 3rd generation heavy metal free OLEDs. However, despite the intense interest, the details of the fundamental processes involved are only now starting to emerge. Much of this understanding has been achieved using a range of theoretical and computational approaches [1]. In this talk I will present our work focusing upon the role of molecular vibrations [2] on reverse intersystem crossing [3]and the activation energy for TADF [4]. Subsequently, the role of the density of excited electronic states and conical intersections is discussed as ways to enhance the rate by directly modifying Fermi’s Golden Rule [5]. Subsequently, the involvement of multiple excited states is discussed in the context of solid states solutions [6] and the interplay between emission width and efficient TADF [7]. Combined, all of these aspects provide the hope for high-level first principles design.

References1. T. J. Penfold et al., Chem. Commun., 54: 3926 - 3935 (2018).2 T. J. Penfold et al. Spin-Vibronic Mechanism for Intersystem Crossing., Chem. Rev., DOI: 10.1021/acs.chemrev.7b00617 (2018).3. J. Gibson et al. ChemPhysChem 17 2956–2961 (2016).4. J Gibson and TJ Penfold et al. Phys. Chem. Chem. Phys. 19:8428 (2017)5 P. L. dos Santos, et al. Adv. Sci., DOI:10.1002/advs.201700989 (2018).6. T. Northey, et al. J. Mater Chem. C 5:11001-11009 (2017).

7. T. Northey and T. J. Penfold, The intersystem crossing mechanism of an ultrapure blue organoboron emitter., Org. Electron., 59:45 (2018).

22nd June – 9.00 am

Multi-reference configuration interaction calculations including spin–orbit coupling havebeen employed to investigate the photophysical properties of various linear NHC-Cu(I)-pyridine complexes with the aim of designing performant thermally-activated delayedfluorescence (TADF) emitters for use in organic light emitting diodes (OLEDs). Ourtheoretical results indicate that this structural motif is very favourable for generatingexcited triplet states with high quantum yield. The first excited singlet (SMLCT) and thecorresponding triplet state (TMLCT) are characterized by 𝑑𝜎 → 𝜋𝑃𝑦 metal-to-ligand charge-

transfer (MLCT) excitations. Efficient intersystem crossing (ISC) and reverse ISC (RISC)between these states is mediated by a near-degenerate second triplet state (TMLCT=LC)with large 𝑑𝜎 → 𝜋𝑃𝑦 contributions. Spin-vibronic coupling is strong and is expected to play

a major role in the (R)ISC processes. The calculations reveal that the luminescence iseffectively quenched by locally excited triplet states if the NHC ligand carries twodiisopropylphenyl (DIPP) substituents. By replacing DIPP with 1-adamantyl residues, thisquenching process is suppressed and TADF is predicted to proceed at a rate of about 1/μs.Introduction of +I substituents on the carbene and -M substituents on the pyridine makes itpossible to tune the emission wavelength from the UV to the blue-green or green spectralregion.

Computer-Aided Design of Luminescent Linear NHC Cu(I) Pyridine Complexes

Christel M. Marian1, Jelena Föller1

1Institute of Theoretical and Computaional Chemistry, Heinrich-Heine-University Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany

22nd June – 9.30 am

One-way and two-way TADF

Tiago Palmeira and Mário Berberan-Santos

CQFM and IBB, Instituto Superior Tecnico, Universidade de Lisboa, Portugal

The kinetics of photoexcited TADF was formulated in terms of excited-state cycles [1], a process wecalled two-way TADF [2]. Recently, a second type of TADF, possible in electroluminescence, wasidentified: One-way TADF [2,3]. For a given efficiency, one-way TADF allows lower rates of reverseintersystem crossing. Graphical and quantitative indicators of singlet-triplet interconversion andphotophysical efficiency will be presented and described with specific examples.

[1] Baleizão C.; Berberan-Santos, M. N., Thermally activated delayed fluorescence as a cycling processbetween excited singlet and triplet states. Application to the fullerenes, J. Chem. Phys. 2007, 126,204510.[2] Palmeira, T; Berberan-Santos, M. N., Kinetic criteria for optimal thermally activated delayedfluorescence (TADF) in photoluminescence and in electroluminescence, J. Phys. Chem. C 2017, 121,701-708.[3] Palmeira, T.; Berberan-Santos, M.N., TADF kinetics and data analysis in photoluminescence andelectroluminescence, in Highly Efficient OLEDs: Materials Based on Thermally Activated DelayedFluorescence, H. Yersin ed., pp. xx-xx, Wiley-VCH, 2018.

22nd June – 10.25 amDesign and Synthesis of All-Organic Small Molecules and Polymers for TADF-OLEDs

Martin R. Bryce

Department of Chemistry, Durham University, Durham, DH1 3LE, UK

This lecture will give an overview from a chemistry perspective of the molecular design criteria for achieving efficientthermally activated delayed fluorescence (TADF) in all-organic donor–acceptor type molecules. Selected examplesfrom the literature will be presented, with particular reference to new molecules synthesised in Durham.[1-7] Keybuilding blocks include functionalised carbazole, phenothiazine, dibenzothiophene-S,S-dioxide and 9,9-dimethylthioxanthene-S,S-dioxide. These molecules probe the importance of the molecular conformation and asmall singlet-triplet energy gap. The photophysical and computational studies on these molecules have provided newinsights into the complexity of the reverse intersystem crossing (RISC) mechanism which leads to efficient TADF insolution and in the solid state. The materials have yielded efficient green, blue and white OLEDs. Polymeric TADFemitters which give solution-processed OLEDs will also be discussed. Representative molecules include:

ReferencesDias, F.B.; Bourdakos, K.N.; Jankus, V.; Moss, K.C.; Kamtekar, K.T.; Bhalla, V.; Santos, J.; Bryce, M.R.;Monkman, A.P., Adv. Mater. 2013, 25, 3707-3714. DOI: 10.1002/adma.201300753.Ward, J.S.; Nobuyasu, R.S.; Batsanov, A.S.; Data, P.; Monkman, A.P.; Dias, F. B; Bryce, M.R., Chem. Commun.2016, 52, 2612-1615. DOI: 10.1039/c5cc09645f.dos Santos, P.L.; Ward, J.S.; Bryce, M.R.; Monkman, A.P., J. Phys. Chem. Lett. 2016, 7, 3341-3346. DOI:10.1021/acs.jpclett.6b01542.Dias, F.B.; Santos, J.; Graves, D.; Data, P.; Nobuyasu, R.S.; Fox, M.A.; Batsanov, A.S.; T. Palmeira, T.; Berberan-Santos, M.N.; Bryce, M.R.; Monkman, A.P. Adv. Sci. 2016, 3, 1600080. DOI: 10.1002/advs.201600080.dos Santos, P.L.; Ward, J.S.; Congrave, D.G.; Batsanov, A.S.; Eng, J.; Stacey, J.E.; Penfold, T.J.; Monkman, A.P.;Bryce, M.R. Adv. Sci. 2018, 1700989. DOI: 10.1002/advs.201700989.Ren, Z.; Nobuyasu, R.S.; Dias, F.B; Monkman, A.P.; Yan, S.; Bryce, M.R., Macromolecules 2016, 49, 5452-5460.DOI: 10.1021/acs.macromol.6b01216.Li, C.; Nobuyasu, R.S.; Wang, Y.; Dias, F.B.; Ren, Z.; Bryce, M.R.; Yan, S. Adv. Opt. Mater. 2017, 1700435. DOI:10.1002/adom.201700435.

22nd June – 10.55 amDESIGN AND SYNTHESIS OF CIRCULARLY POLARIZED THERMALLY ACTIVATEDDELAYED FLUORESCENCE EMITTERS

Grégory Pietersa

a SCBM, CEA, Université Paris Saclay, 91191Gif-sur-Yvette Cedex, France

The differential emission of right- and left-circularly polarized light by a chiral molecule is known as circularly polarized luminescence (CPL). Molecules exhibiting CPL properties can be used for the construction of avant-garde photonics devices such as 3D displays, information storage and processing or spintronic-based devices.[1] Such chiralcompounds are also centerpieces in the design of Circularly Polarized Organic Light Emitting Diodes (CP-OLED) where they are used as emissive dopants. Recently, the development of CP-OLED has received renewed attention as a potential direction for increasing the energy efficiency and the contrast of conventional OLED displays in which 50% of the light emitted is suppressed through the use of a polarizer and a quarter-wave plate to reduce the external light reflection.[2] This high energy loss can be overcome using CP-OLED because the circularly generated electroluminescence can pass these filters without any attenuation, resulting in a strong increase of display performances. So far, combining a high polarization of electroluminescence with state-of-the-art OLED performances in terms of luminance and efficiency remains a considerable scientific challenge. In this context, we have developed a class of purely organic luminophores that combines CPL with TADF in a modular design, and exhibits attractive photophysical properties.3 This presentation will disclose the concept, preparation, and properties of this new class of molecules, and present their application in OLED devices. Structure-properties relationships have also been explored and will be discussed.

References[1]: a) Brandt, J. R.; Salerno, F.; Fuchter, M. J. Nat. Rev. Chem. 2017, article 00452017; b) Sánchez-Carnerero, E. M.; Agarrabeitia, A. R.; Moreno, F.; Maroto, B. L.; Muller, G.; Ortiz, M. J.; de la Moya, S. Chem. - Eur. J. 2015, 21, 13488 ; c) Kumar, J.; Nakashima, T.; Kawai, T. J. Phys. Chem. Lett. 2015, 6, 3445.[2]: a) Brandt, J. R.; Wang, X.; Yang, Y.; Campbell, A. J.; Fuchter, M. J. J. Am. Chem. Soc. 2016, 138, 9743; b) Zinna, F.; Giovanella, U.; Di Bari, L. Adv. Mater. 2015, 27, 1791-1795; c) Li, T.-Y.; Jing, Y.-M.; Liu, X.; Zhao, Y.; Shi, L.; Tang, Z.; Zheng, Y.-X.; Zuo, J.-L. Sci. Rep. 2015, 5, 14912; d) Yang, Y.; da Costa, R. C.; Smilgies, D.-M.; Campbell, A. J.; Fuchter, M. J. Adv. Mater. 2013, 25, 2624[3] Feuillastre, S.; Pauton, M.; Gao, L.; Desmarchelier, A.; Riives, A. J.; Prim, D.; Tondelier, D.; Geffroy, B.; Muller, G.; Clavier G.; Pieters, G. J. Am. Chem. Soc. 2016, 138, 3990

22nd June – 11.25 am

Synthesis and Properties of New Helicene-Based Thermally ActivatedDelayed Fluorescence Molecules.

A. Klimash1, P. Pander2, F. B. Dias2, P. J. Skabara1

1School of Chemistry, University of Glasgow, Glasgow, UK 2Department of Physics, Durham University, Durham, UK

Thermally activated delayed fluorescence (TADF) in purely organic materials has emerged as the alternative way toachieve the internal quantum efficiency in organic materials close to 100%1. TADF characteristics are highly dependenton molecule’s structure, therefore the design and synthesis of appropriate compounds as well as the betterunderstanding of structure-property relationships are required. For example, despite the significant amount of TADFmaterials reported up to date, only few studies are dedicated to the behavior of TADF emitters in pure solid state.Helicenes belong to a family of polycyclic aromatic hydrocarbons (PAHs). Their non-planar chiral structure is the resultof the intramolecular steric repulsion, as they consist of several ortho-fused aromatic rings. Recently helicenes wereconsidered as suitable materials for OLEDs2,3.Here we present two new donor-acceptor and donor-acceptor-donor TADF molecules H1- and H2-PXZ based onmono- and diaza[5]helicene cores4, and discuss how the photophysical properties of these emitters are influenced bytheir crystal structure.

AcknowledgementsThis work was performed in the framework of the EXCILIGHT project, funded by the European Union Horizon 2020research and innovation programme under the Marie Sklodowska-Curie grant agreement No 674990.

1. Endo, A. et al. Appl. Phys. Lett. 98, 83302 (2011).2. Sahasithiwat, S., Mophuang, T., Menbangpung, L., Kamtonwong, S. & Sooksimuang, T. Synth. Met. 160, 1148–1152 (2010).3. Hua, W. et al. RSC Adv 5, 75–84 (2015).4. Waghray, D. et al. J. Org. Chem. 77, 10176–10183 (2012).

22nd June – 11.55 am

Electrochemical characterization of organic materials for optoelectronic applications

Sandra Pluczyk, Pawel Zassowski, Mieczyslaw Lapkowski

Faculty of Chemistry, Silesian University of Technology, Poland,

The determination of redox properties is one of the basic, however crucial task during the evaluation of new electroactivematerials for the wide range of application. In this terms, the electrochemistry is a suitable method, providing a number of valuableinformation about redox properties, stability, the conversion and storage of energy, etc. It also allows to determine the electronaffinity and ionization energy of investigated compounds, parameters which are correlated with energies of HOMO and LUMOlevel, which need to be determined if materials are investigated towards optoelectronic applications. The analysis ofelectrochemical results allows also to make preliminary conclusions about electronic coupling in molecule, especially when theseries of materials are investigated to define the relationship between the chemical structure and properties. The combine theelectrochemistry with spectroscopic techniques gives even deeper insight into processes which investigated materials undergounder influence of applied voltage. It makes possible to characterize species which are formed as intermediates or as products ofredox processes as well as to investigate generation and the dynamics of formed charge carriers. Moreover, it is helpful inelucidation mechanism of electrode reactions.

The basics and examples of electrochemical and spectroelectrochemical analysis of bipolar organic materials will be presented. Inthis regard such techniques as e.g. cyclic and differentials pulse voltammetry as well as UV-Vis-NIR and electron paramagneticresonance spectroelectrochemistry applied to investigations of new materials will be discussed.