Photophysical, optical and luminescent characteristics of heterocyclic-substituted coumarins and their application in OLED-devices

   The development of organic electronics stimulates the search for new materials. The priority task is to find compounds with high brightness, efficiency and stability of luminescence. Coumarin derivatives are considered as promising candidates for solving this problem. This paper presents the results of a study of organic light-emitting diodes in the emission layer of which a number of coumarin dyes with pronounced donor-acceptor properties are used.

   The aim of the study was to identify the influence of the structure of synthesized molecules on the photophysical characteristics as well as on the emission efficiency of LEDs based on them.

   A series of organic compounds of the coumarin series has been synthesized: (E)-3-(3-(anthracene-9-yl)acryloyl)coumarin (compound 1), 4-hydroxy-3-(5-(4-methoxyphenyl)-1-(p-tolyl)-4,5-dihydro-1H-pyrazol-3-yl)coumarin (compound 2), 3-(1-acetyl-5-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-3-yl)-4-hydroxycoumarin (compound 3), ethyl 7-(diethylamino)Coumarin-3-carboxylate (compound 4) as well as the well-known laser dye Coumarin 6 (3-(benzo[d]thiazole-2-yl)-7-(diethylamino)coumarin) used as a reference compound. The LEDs were produced by vacuum thermal spraying and spin-coating. The fluorescence and electroluminescence spectra were studied using an Ocean Optics Maya 200 PRO spectrometer. A photomultiplier was used to obtain the luminescence decay curves, PicoQuant PMA-C 192-N-M. Spectral data (absorption, photoluminescence) as well as time-resolved measurements (fluorescence attenuation time) indicate the key role of donor-acceptor interactions as well as spatial effects in the formation of electronic transitions. The current-voltage characteristics confirmed the presence of conduction modes limited by spatial charge and conduction limited by carrier capture processes. The study of the voltage-brightness characteristics showed that compound 2 demonstrates brightness comparable to the reference compound Coumarin 6, which makes it the most promising for further optimization of organic light-emitting diodes. In addition, it is shown that compound 4 in the device provides white emission with chromaticity coordinates close to daylight, which makes it potentially possible for practical use in lighting systems. The data obtained confirm the influence of donor-acceptor interactions on the properties of coumarins. The degree of conjugation of donor and acceptor fragments is directly determined by spectral shifts in the absorption and fluorescence spectra. The high brightness of compound 2-based diodes, comparable to the Cou standard, is due to its efficient donor-acceptor system which optimizes intramolecular charge transfer and increases the likelihood of radiative transitions (long lifetime of the excited state 3.5 ns). On the contrary, the acetyl group in compound 3 disrupts conjugation, leading to low brightness and short fluorescence lifetime (1.7 ns) due to nonradiative relaxation. The ability of compound 4 to provide white radiation in diodes (correlated color temperature 6410 K, close to daylight) is related to the contribution of the electron transport layer to the emission spectrum.

1. Song J., Guan Y., Wang C., Li W., Bao X., Niu L. Effect of conductive polymers PEDOT:PSS on exciton recombination and conversion in doped-type BioLEDs. Polymers, 2023, vol. 15, no. 15, pp. 3275. doi: 10.3390/polym15153275

2. Kim J., Jeon M.-G., Yun S., Kirakosyan A., Choi J. Suppressing metal cation diffusion in perovskite light-emitting diodes via blending amino acids with PEDOT:PSS. ACS Photonics, 2025, vol. 12, no. 2, pp. 971–980. doi: 10.1021/acsphotonics.4c02027

3. Liu R., Yu T., Su R., Zhao Y., Zhang D., Zhang S., Su W. Photo-and electroluminescent properties of V-shaped fused-biscoumarins containing tert-butyl group modified imidazole/carbazole groups. Organic Electronics, 2025, vol. 139, pp. 107208. doi: 10.1016/j.orgel.2025.107208

4. Osadchenko A.V., Ambrozevich S.A., Zakharchuk I.A., Vashchenko A.A., Daibagya D.S., Ryzhov A.V., et al. Organic light-emitting diodes based on Eu(III) complexes involving 1,1,1-trifluoro-4-phenyl-2,4-butanedione with ethanoic and n-butanoic acids. Physics of Wave Phenomena, 2025, vol. 33, no. 1, pp. 72–77. doi: 10.3103/S1541308X24700559

5. Jia Z., Xie X., Guo Z., Kou Z. High-CRI warm white OLEDs based on TADF-doped exciplex co-host structure enabled by efficient reverse intersystem crossing. Organic Electronics, 2025, vol. 141, pp. 107229. doi: 10.1016/j.orgel.2025.107229

6. Osadchenko A.V., Ambrozevich S.A., Zakharchuk I.A., Vashchenko A.A., Daibagya D.S., Ryzhov A.V., Pevtsov D.N., Pevtsov N.V., Selyukov A.S. Electroluminescence of new coordination compounds of europium ions with β-diketones, acetic and butyric acids. Scientific and Technical Journal of Information Technologies, Mechanics and Optics, 2024, vol. 24, no. 4, pp. 570–576. (in Russian). doi: 10.17586/2226-1494-2024-24-4-570-576

7. Cao Y., Wang N., Tian H., Guo J., Wei Y., Chen H., et al. Perovskite light-emitting diodes based on spontaneously formed submicrometre-scale structures. Nature, 2018, vol. 562, no. 7726, pp. 249–253. doi: 10.1038/s41586-018-0576-2

8. Chiba T., Hayashi Y., Ebe H., Hoshi K., Sato J., Sato S., PuY.-J., Ohisa Kido J. Anion-exchange red perovskite quantum dots with ammonium iodine salts for highly efficient light-emitting devices. Nature Photonics, 2018, vol. 12, no. 11, pp. 681–687. doi: 10.1038/s41566-018-0260-y

9. Lin K., Xing J., Quan L.N., de Arquer F.P.G., Gong X., Lu J., et al. Perovskite light-emitting diodes with external quantum efficiency exceeding 20 per cent. Nature, 2018, vol. 562, no. 7726, pp. 245–248. doi: 10.1038/s41586-018-0575-3

10. Liu Y., Cui J., Du K., Tian H., He Z., Zhou Q., et al. Efficient blue light-emitting diodes based on quantum-confined bromide perovskite nanostructures. Nature Photonics, 2019, vol. 13, no. 11, pp. 760–764. doi: 10.1038/s41566-019-0505-4

11. Li C.H.A., Zhou Z., Vashishtha P., Halpert J.E. The future is blue (LEDs): why chemistry is the key to perovskite displays. Chemistry of Materials, 2019, vol. 31, no. 16, pp. 6003–6032. doi: 10.1021/acs.chemmater.9b01650

12. Wang Q., Wang X., Yang Z., Zhou N., Deng Y., Zhao J., et al. Efficient sky-blue perovskite light-emitting diodes via photoluminescence enhancement. Nature Communications, 2019, vol. 10, no. 1, pp. 5633. doi: 10.1038/s41467-019-13580-w

13. Kang S., Jillella R., Jeong J., Park Y.-I., Pu Y.-J., Park J. Improved electroluminescence performance of perovskite light-emitting diodes by a new hole transporting polymer based on the benzocarbazole moiety. ACS Applied Materials and Interfaces, 2020, vol. 12, no. 46, pp. 51756–51765. doi: 10.1021/acsami.0c16593

14. Zhang X., Guo M., Li J., Dai T., Yang Z., Lou Z., et al. Low-voltage RGB perovskite light-emitting transistors with magnetron sputtered Ta₂O₅ high-k dielectric layer. Organic Electronics, 2025, vol. 142, pp. 107241. doi: 10.1016/j.orgel.2025.107241

15. Worku M., Ben-Akacha A., Shonde T.B., Liu H., Ma B. The past, present, and future of metal halide perovskite light-emitting diodes. Small Science, 2021, vol. 1, no. 8, pp. 2000072. doi: 10.1002/smsc.202000072

16. Yu T., Zhang P., Zhao Y., Zhang H., Meng J., Fan D., Chen L., Qiu Y. Synthesis, crystal structure and photo- and electro-luminescence of the coumarin derivatives with benzotriazole moiety. Organic Electronics, 2010, vol. 11, no. 1, pp. 41–49. doi: 10.1016/j.orgel.2009.09.023

17. Zhang H., Chai H., Yu T., Zhao Y., Fan D. High-efficiency blue electroluminescence based on coumarin derivative 3-(4-(anthracen-10-yl)phenyl)-benzo[5,6]coumarin. Journal of Fluorescence, 2012, vol. 22, no. 6, pp. 1509–1512. doi: 10.1007/s10895-012-1088-3

18. Shreykar M.R., Sekar N. Stimuli-responsive luminescent coumarin thiazole hybrid dye: synthesis, aggregation induced emission, thermochromism and DFT study. Dyes and Pigments, 2017, vol. 142, pp. 121–125. doi: 10.1016/j.dyepig.2017.03.028

19. Zhang H., Liu X., Gong Y., Yu T., Zhao Y. Synthesis and characterization of SFX-based coumarin derivatives for OLEDs. Dyes and Pigments, 2021, vol. 185, part A, pp. 108969. doi: 10.1016/j.dyepig.2020.108969

20. Zhang H., Luo Q., Mao Y., Zhao Y., Yu T. Synthesis and characterization of coumarin-biphenyl derivatives as organic luminescent materials. Journal of Photochemistry and Photobiology A: Chemistry, 2017, vol. 346, pp. 10–16. doi: 10.1016/j.jphotochem.2017.05.039

21. Traven V.F., Cheptsov D.A., Svetlova J.I., Ivanov I.V., Cuerva C., Lodeiro С. et al. The role of the intermolecular π⋯π interactions in the luminescence behavior of novel coumarin-based pyrazoline materials. Dyes and Pigments, 2021, vol. 186, pp. 108942. doi: 10.1016/j.dyepig.2020.108942

22. Traven V.F., Cheptsov D.A., Bulanova M.V., Solovjova N.P., Chibisova T.A., Dolotov S.M., Ivanov I.V., et al. On the mechanism of photodehydrogenation of aryl(hetaryl)pyrazolines in the presence of perchloroalkanes. Photochemistry and Photobiology, 2018, vol. 94, no. 4, pp. 659–666. doi: 10.1111/php.12918

23. Secci D., Carradori S., Bolasco A., Chimenti P., Yáñez M., Ortuso F., Alcaro S., et al. Synthesis and selective human monoamine oxidase inhibition of 3-carbonyl, 3-acyl, and 3-carboxyhydrazido coumarin derivatives. European Journal of Medicinal Chemistry, 2011, vol. 46, no. 10, pp. 4846–4852. doi: 10.1016/j.ejmech.2011.07.017

24. Huang Z.-L., Li N., Sun Y., Wang H., Song H., Xu Z. Synthesis and structure–photophysical property relationships for two coumarinyl-based two-photon induced fluorescent molecules. Journal of Molecular Structure, 2003, vol. 657, no. 1-3, pp. 343–350. doi: 10.1016/S0022-2860(03)00427-7

25. Lee S., Sivakumar K., Shin W-S., Xie F., Wang Q. Synthesis and anti-angiogenesis activity of coumarin derivatives. Bioorganic & Medicinal Chemistry Letters, 2006, vol. 16, no. 17, pp. 4596–4599. doi: 10.1016/j.bmcl.2006.06.007

26. Shreykar M.R., Sekar N. Coumarin-pyrazole hybrid with red shifted ESIPT emission and AIE characteristics — a comprehensive study. Journal of Fluorescence, 2017, vol. 27, no. 5, pp. 1687–1707. doi: 10.1007/s10895-017-2106-2

27. Gawad S.A.A., Sakr M.A.S. Spectroscopic investigation, DFT and TD-DFT calculations of 7-(Diethylamino) Coumarin (C466). Journal of Molecular Structure, 2022, vol. 1248, pp. 131413. doi: 10.1016/j.molstruc.2021.131413

28. Yang L., Liu Y., Zhou X., Wu Y., Ma C., Liu W., Zhang C. Asymmetric anthracene-fused BODIPY dye with large Stokes shift: synthesis, photophysical properties and bioimaging. Dyes and Pigments, 2016, vol. 126, pp. 232–238. doi: 10.1016/j.dyepig.2015.11.028

29. Felorzabihi N., Haley J.C., Bardajee G.R., Winnik M.A. Systematic study of the fluorescence decays of amino-coumarin dyes in polymer matrices. Journal of Polymer Science Part B: Polymer Physics, 2007, vol. 45, no. 17, pp. 2333–2343. doi: 10.1002/polb.21226

30. Altalbawy F.M.A., Abdelkader M.H., Darwish E.S.S., Elnagdi M.H. Synthesis, electronic absorption, fluorescence and live time spectroscopic study of some new 3,7-disubstituted coumarin derivatives as new fluorescent probes. Asian Journal of Chemistry, 2016, vol. 28, no. 10, pp. 2303–2310. doi: 10.14233/ajchem.2016.19975

31. Takizawa S., Montes V.A., Anzenbacher P. Phenylbenzimidazole-based new bipolar host materials for efficient phosphorescent organic light-emitting diodes. Chemistry of Materials, 2009, vol. 21, no. 12, pp. 2452–2458. doi: 10.1021/cm9004954

32. Kotchapadist P., Prachumrak N., Sunonnam T., Namuangruk S., Sudyoadsuk T., Keawin T., et al. Synthesis, characterisation, and electroluminescence properties of N-coumarin derivatives containing peripheral triphenylamine. European Journal of Organic Chemistry, 2015, vol. 2015, no. 3, pp. 496–505. doi: 10.1002/ejoc.201402680

33. Sahoo R.K., Atta S., Singh N.D.P., Jacob C. Influence of functional derivatives of an amino-coumarin/MWCNT composite organic hetero-junction on the photovoltaic characteristics. Materials Science in Semiconductor Processing, 2014, vol. 25, pp. 279–285. doi: 10.1016/j.mssp.2014.01.001

34. Osadchenko A.V., Vashchenko A.A., Zakharchuk I.A., Daibagya D.S., Ambrozevich S.A., Volodin N.Yu., Cheptsov D.A., Dolotov S.M., Traven V.F., Avramenko A.I., Semenova S.L., Selyukov A.S. Organic light-emitting diodes with new dyes based on coumarin. Scientific and Technical Journal of Information Technologies, Mechanics and Optics, 2022, vol. 22, no. 6, pp. 1112–1118. (in Russian). doi: 10.17586/2226-1494-2022-22-6-1112-1118