Rational Design of a blue TADF Emitter Family using a Trifluoromethylphenyl Core

Transcription

1 Rational Design of a blue TAD Emitter amily using a Trifluoromethylphenyl Core Ramunas Lygaitis, Paul Kleine, Reinhard Scholz, Ludwig Popp, Olaf Zeika, Simone Lenk, and Sebastian Reineke Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics TU Dresden, Germany Kaunas university of Technology, Lithuania XXII IKSS Krutyn Poland

2 DRESDE old city new technologies

3 Motivation Issues holding back OLEDs, from gaining a major fraction of the world lighting markets: Iridium based blue phosphors are not sufficiently stable Iridium is a unsustainable resource Therefore, new types of emitters, particularly for blue, are required to replace the current iridium complexes olie 3 von XYZ

4 Thermally Activated Delayed luorescence Emitters which show Thermally Activated Delayed luorescence could harvest triplet excitons therefore device efficiency could be comparable to PhOLED Diagram provided by Sebastian Reineke olie 4 von XYZ

5 Thermally Activated Delayed luorescence TAD could originate from: molecules with Intramolecular Charge Transfer (ICT) donor-acceptor complexes in excited state (exciplexes) olie 5 von XYZ

6 Design of molecules or the design of ICT molecules were exploited two strategies: J. Am. Chem. Soc., 2014, 136 (52), pp Those design rules lead to: - Bipolar compounds with spatially separated HOMO and LUMO - Small energy difference between the T and S states (ΔEST); olie 6 von XYZ

7 State of the art example umber, origin and position of the donors influence the emission colour H. Uoyama et al. ature, 492, 234, olie 7 von XYZ

8 Acceptor design ew TAD materials donor: carbazole (or similar) strong acceptor: phenyl-(c)2 H. Uoyama, K. Goushi, K. Shizu, H. omura, C. Adachi, ature 492, 234 (2012) weaker acceptor: phenyl--c3, larger CT gap expected DT calculations: B3LYP/6-31g(d) olie 8 von XYZ

9 Design strategy ew TAD materials donor: carbazole (or similar) strong acceptor (Adachi group): phenyl-(c)2 weaker acceptor: phenyl--c3: larger CT gap expected Time-dependent DT calculations: B3LYP/6-31g(d) olie 9 von XYZ

10 Design strategy - Phenylcarbazoles C3 1Cz4C3 C3 2Cz3C3 C3 C3 3Cz2C3 4Cz1C3 C3 5CzC3 olie 10 von XYZ

11 Synthetic procedure - Phenylcarbazoles C3 C3 1.2 eq Cz, 1 eq OT, K2CO3, DM, RT, 18h C3 5 eq Cz, 1 eq OT, ah, DM, RT, 30 min C3 + 2 eq Cz, 1 eq OT, K2CO3, DM, RT, 18h H 2.7 eq Cz, 1 eq OT, KOH, acetone, reflux, 1h C3 4 eq Cz, 1 eq OT, ah, DM, RT, 20 min C3 olie 11 von XYZ

12 MR spectra of Phenylcarbazoles 19 olie 12 von XYZ

13 2D MR of 5CzC3 olie 13 von XYZ

14 Characterisation by single-crystal XRD 1Cz4C3 2Cz3C3 3Cz2C3 5CzC3 olie 14 von XYZ

15 Characterisation by single-crystal XRD olie 15 von XYZ

16 Characterisation by single-crystal XRD 5CzC3 Projection of the (a,c)-plane in 5CzC3 olie 16 von XYZ

17 Characterisation by single-crystal XRD 5CzC3 Projection of the (a,b)-plane in 5CzC3 olie 17 von XYZ

18 Analysis of XRD data The Hirshfeld surface1,2 of a molecule in a crystal of 5CzC3 - close contacts between neighbour molecules do not exist [1] J.J. McKinnon, M.A. Spackman, A.S. Mitchell, Acta Cryst. B, 2004,60, 627 [2] M.A. Spackman, P.G. Byrom, Chem. Phys. Lett., 1997, 267, 215 olie 18 von XYZ

19 Analysis of XRD data Contributions to the Hirshfeld surface 1Cz4C3 H 2Cz3C3 CC 3Cz2C3 CH 5CzC3 0% HH 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% p-p stacking (C-C contribution) is negligible in 5CzC3 Decrease in number of carbazole units in the molecules lead in increase of p-p stacking amount in the crystal olie 19 von XYZ

20 Characterisation by CV - Phenylcarbazoles olie 20 von XYZ

21 Thermal characterisation by TGA 1Cz4C3 2Cz3C3 3Cz2C3 4CzC3 5CzC3 100 Mass/% 80 Initial decomposition temperatures: 360oC 400oC 460oC o Temperature, C olie 21 von XYZ

22 Photophysical investigation - Emission peakings of toluene solutions 2Cz3C3 C3 464 nm 3Cz2C3 C3 454 nm 4Cz1C3 C3 5CzC3 C3 477 nm 482 nm olie 22 von XYZ

23 Photophysical investigation - absorption by CT states - Broad unstructured 1CT emission - Solvatochromic shift observed for all compounds olie 23 von XYZ

24 Photophysical investigation - Identification of two mono-exponential decay regimes - Strong delayed fluorescence (D) contribution for 5CzC3 - Up-conversion process is assigned to TAD olie 24 von XYZ

25 Photophysical investigation Photophysical data Compound ΦPL ΦP/ ΦD/ /% % % S1/ ev τp/ ns τd/ krisc/ s-1 µs knr/ s-1 ΔEST/ mev Cz4C Cz3C Cz2C CzC CzC olie 25 von XYZ

26 Sky blue OLED olie 26 von XYZ

27 OLED optimization olie 27 von XYZ

28 White OLED olie 28 von XYZ

29 White OLED olie 29 von XYZ

30 Two-colour white Good colour rendering index Correlated colour temperature around 3000 K olie 30 von XYZ

31 Summary Theory-based design of new TAD materials with large gaps D-A type TAD emitters showing blue PL emission from 453 to 490 nm have been synthesized and characterized Time-dependent spectra prove TAD mechanism ΔEST decrease while internal repulsion between D and A units increase breaking HOMO-LUMO conjugation External quantum efficiency in sky blue OLEDs exceeds singlet emitters Colour coordinate of emitter allows for two-colour white OLED 5CzC3, toluene olie 31 von XYZ

32 Acknowledgements Heather Cole (Durham) Marc Etherington (Durham) Andy Monkman (Durham) GA (CEOSeR) P 7 GA (PHEBE) Horizon 2020 Thank you for your attention! olie 32 von XYZ

33 5CzC3 olie 33 von XYZ