Abstract
Thermally activated delayed fluorescence (TADF) is one of the most attractive photophysical properties due to its potential application as a triplet harvesting mechanism in metal-free OLED emitters. TADF shows a way to achieve 100% theoretical internal quantum efficiency by thermally up-converting the non-radiative triplet excitons. Initially, the mechanism of TADF was proposed to be based on the thermal equilibrium of the lowest singlet (S1) and triplet (T1) states, where the rate constant for reverse intersystem crossing (kRISC) was dependent on the temperature. At the same time, the flipping of spin in TADF is considered to be the result of spin–orbit coupling. Recent findings showed that the TADF and organic room temperature phosphorescence (RTP) property of a purely organic emitter can be tuned by steric hindrance between donor and acceptor groups in D-A-D molecules. The intersystem crossing between triplet charge transfer (3CT) and triplet local exciton (3LE) states depends on the extent of vibronic coupling and the adiabatic energy difference between them. Furthermore, the optimal energy gap of 1CT and 3CT and 3CT and 3LE states is important for efficient TADF. Overall, there are several factors involved in designing the materials for efficient TADF. Herein, we briefly review the fundamental mechanism, photophysical kinetics, and different theories of TADF along with the photophysical characterization of some organic TADF molecules. Also, the applications of some of the TADF materials in OLEDs were summarized.
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References
Aizawa, N., Harabuchi, Y., Maeda, S., Pu, Y.J.: Kinetic prediction of reverse intersystem crossing in organicdonor–acceptor molecules. Nat. Commun. 11, 1–6 (2020)
Albrecht, A.C.: Vibronic—spin-orbit perturbations and the assignment of the lowest triplet state of benzene. J. Chem. Phys. 38(2), 354–365 (1963)
Awasthi, A.A., Gupta, N., Siddiqui, Q.T., Parab, P., Palit, D.K., Bose, S., Agarwal, N.: Synthesis of acridone-naphthylamine derivative and its thermally-activated delayed fluorescence studies for application in OLEDs. J. Chem. Sci. 131, 1–8 (2019)
Chen, T., Zheng, L., Yuan, J., An, Z., Chen, R., Tao, Y., Li, H., Xie, X., Huang, W.: Understanding the control of singlet-triplet splitting for organic exciton manipulating: a combined theoretical and experimental approach. Sci. Rep. 5, 1–11 (2015a)
Chen, X.K., Zhang, S.F., Fan, J.X., Ren, A.M.: Nature of highly efficient thermally activated delayed fluorescence in organic light-emitting diode emitters: nonadiabatic effect between excited states. J. Phys. Chem. C 119, 9728–9733 (2015b)
Cho, Y.J., Yook, K.S., Lee, J.Y.: Cool and warm hybrid white organic light-emitting diode with blue delayed fluorescent emitter both as blue emitter and triplet host. Sci. Rep. 5, 1–7 (2015a)
Cho, Y.J., Jeon, S.K., Chin, B.D., Yu, E., Lee, J.Y.: The design of dual emitting cores for green thermally activated delayed fluorescent materials. Angew. Chem. Int. Ed. 54, 5201–5204 (2015b)
Cho, Y.J., Chin, B.D., Jeon, S.K., Lee, J.Y.: 20% external quantum efficiency in solution-processed blue thermally activated delayed fluorescent devices. Adv. Funct. Mater. 25, 6786–6792 (2015c)
Data, P., Pander, P., Okazaki, M., Takeda, Y., Minakata, S., Monkman, A.P.: Dibenzo[a j]Phenazine-cored donor-acceptor-donor compounds as green-to-red/NIR thermally activated delayed fluorescence organic light emitters. Angew. Chemie Int. Ed. 55, 5739–5744 (2016)
Data, P., Okazaki, M., Minakata, S., Takeda, Y.: Thermally activated delayed fluorescence: vs. room temperature phosphorescence by conformation control of organic single molecules. J. Mater. Chem. C 7, 6616–6621 (2019)
Deng, C., Zhang, L., Wang, D., Tsuboi, T., Zhang, Q.: Exciton-and polaron-induced reversible dipole reorientation in amorphous organic semiconductor films. Adv. Opt. Mater. 7, 1801644 (2019)
Dias, F.B., Santos, J., Graves, D.R., Data, P., Nobuyasu, R.S., Fox, M.A., Batsanov, A.S., Palmeira, T., Berberan-Santos, M.N., Bryce, M.R., Monkman, A.P.: The role of local triplet excited states and d-a relative orientation in thermally activated delayed fluorescence: photophysics and devices. Adv. Sci. 3, 1–10 (2016)
Dias, F.B., Penfold, T.J., Monkman, A.P.: Photophysics of thermally activated delayed fluorescence molecules. Methods Appl. Fluoresc. 5, 12001 (2017)
Dias, F.B., Bourdakos, K.N., Jankus, V., Moss, K.C., Kamtekar, K.T., Bhalla, V., Santos, J., Bryce, M.R., Monkman, A.P.: Triplet harvesting with 100% efficiency by way of thermally activated delayed fluorescence in charge transfer OLED emitters. Adv. Mater. 25, 3707 (2013)
Dixit, S.J.N., Gupta, C.V., Naidu, G.S., Bose, S., Agarwal, N.: Peri-N-amine-perylenes with and without phenyl bridge: photophysical studies and their OLED applications. J. Photochem. Photobio. a: Chem. 426, 113710 (2022)
Edwards, A.A., Alexander, B.D.: UV-Visible absorption spectroscopy organic applications. In: Encyclopedia of spectroscopy and spectrometry, pp. 511–519 (2017)
Endo, A., Sato, K., Yoshimura, K., Kai, T., Kawada, A., Miyazaki, H., Adachi, C.: Efficient up-conversion of triplet excitons into a singlet state and its application for organic light emitting diodes. Appl. Phys. Lett. 98, 2011–2014 (2011)
Etherington, M., Gibson, J., Higginbotham, H., et al.: Revealing the spin–vibronic coupling mechanism of thermally activated delayed fluorescence. Nat. Commun. 7, 13680 (2016)
Gibson, J., Monkman, A.P., Penfold, T.J.: The importance of vibronic coupling for efficient reverse intersystem crossing in thermally activated delayed fluorescence molecules. ChemPhysChem 1, 2956–2961 (2016)
Hosokai, T., Matsuzaki, H., Furube, A., Tokumaru, K., Nakanotani, H., Yahiro, M., Adachi, C.: Revealing the excited-state dynamics of thermally activated delayed fluorescence molecules by using transient absorption spectroscopy 786–789 (2016)
Koseki, S., Schmidt, M.W., Gordon, M.S.: Calculations of one-electron spin-orbit coupling constants in diatomic molecules. J. Phys. Chem. 96, 10768–10772 (1992)
Kretzschmar, A., Patze, C., Schwaebel, S.T., Bunz, U.H.F.: Development of thermally activated delayed fluorescence materials with shortened emissive lifetimes. J. Org. Chem. 80, 9126–9131 (2015)
Lee, K., Kim, D.: Local-excitation versus charge-transfer characters in the triplet state: theoretical insight into the singlet-triplet energy differences of carbazolyl-phthalonitrile-based thermally activated delayed fluorescence materials. J. Phys. Chem. C 120, 28330–28336 (2016)
Lee, D.R., Hwang, S.H., Jeon, S.K., Lee, C.W., Lee, J.Y.: Benzofurocarbazole and Benzothienocarbazole as donors for improved quantum efficiency in blue thermally activated delayed fluorescent devices. Chem. Commun. 51, 8105–8107 (2015)
Lee, S.M., Ju, B.K., Lee, C.J.: Temperature dependence of the driving properties for a green thermally activated delayed fluorescence device with a mixed host. Thin Solid Films 660, 166–170 (2017)
Lewis, G.N., Lipkin, D.: Reversible photochemical processes in rigid media. a study of the phosphorescent state. J. Am. Chem. Soc. 63, 3005–3018 (1941)
Li, B., Nomura, H., Miyazaki, H., Zhang, Q., Yoshida, K., Suzuma, Y., Orita, A., Otera, J., Adachi, C.: Dicarbazolyldicyanobenzenes as thermally activated delayed fluorescence emitters: effect of substitution position on photoluminescent and electroluminescent properties. Chem. Lett. 43(3), 319–321 (2014)
Li, N., Ni, F., Lv, X., Huang, Z., Cao, X., Yang, C.: Host-dopant interaction between organic thermally activated delayed fluorescence emitter and host material: insight into the excited state. Adv. Optical Mater. 10, 2101343 (2022)
Lim, B.T., Okajima, S., Chandra, A.K., Lim, E.C.: Radiationless transitions in electron donor-acceptor complexes: selection rules for S1 → T intersystem crossing and efficiency of S1 → S0 internal conversion. Chem. Phys. Lett. 79(1), 22–27 (1981)
Lin, L., Fan, J., Cai, L., Wang, C.K.: Excited state dynamics of new-type thermally activated delayed fluorescence emitters: theoretical view of light-emitting mechanism. Mol. Phys. 116, 19–28 (2014)
Liu, W., Zheng, C.J., Wang, K., Chen, Z., Chen, D.Y., Li, F., Ou, X.M., Dong, Y.P., Zhang, X.H.: Novel carbazol-pyridine-carbonitrile derivative as excellent blue thermally activated delayed fluorescence emitter for highly efficient organic light-emitting devices. ACS Appl. Mater. Interfaces 7, 18930–18936 (2015)
Liu, J., Li, Z., Hu, T., Wei, X., Wang, R., Hu, X., Liu, Y., Yi, Y., Yamada-Takamura, Y., Wang, Y., Wang, P.: Experimental evidence for “Hot Exciton” thermally activated delayed fluorescence emitters. Adv. Opt. Mater. 7, 1–9 (2019)
Marian, C.M.: Mechanism of the triplet-to-singlet up-conversion in the assistant dopant ACRXTN. J. Phys. Chem. C 120, 3715–3721 (2016)
Méhes, G., Goushi, K., Potscavage, W.J., Adachi, C.: Influence of host matrix on thermally activated delayed fluorescence: effects on emission lifetime, photoluminescence quantum yield, and device performance. Org. Electron. 15(9), 2027–2037 (2014)
MĂ©hes, G., Sandanayaka, A.S.D., Ribierre, J.C., Goushi, K.: Physics and design principles of OLED devices. In: Adachi, C., Hattori, R., Kaji, H., Tsujimura, T. (eds.) Handbook of Organic Light-Emitting Diodes. Springer, Tokyo (2020). https://doi.org/10.1007/978-4-431-55761-6_49-1
Niwa, A., Kobayashi, T., Nagase, T., Goushi, K., Adachi, C., Naito, H.: Temperature dependence of photoluminescence properties in a thermally activated delayed fluorescence emitter. Appl. Phys. Lett. 104, 213303 (2014)
Northey, T., Stacey, J., Penfold, T.J.: The role of solid-state solvation on the charge transfer state of a thermally activated delayed fluorescence emitter. J. Mater. Chem. C 5, 11001–11009 (2017)
Ogiwara, T., Wakikawa, Y., Ikoma, T.: Mechanism of intersystem crossing of thermally activated delayed fluorescence molecules. J. Phys. Chem. A 119, 3415–3418 (2015)
Pan, Y., Li, W., Zhang, S., Yao, L., Gu, C., Xu, H., Yang, B., Ma, Y.: High yields of singlet excitons in organic electroluminescence through two paths of cold and hot excitons. Adv. Opt. Mater. 2, 510–515 (2014)
Park, I.S., Lee, S.Y., Adachi, C., Yasuda, T.: Full-color delayed fluorescence materials based on wedge-shaped phthalonitriles and dicyanopyrazines: systematic design tunable photophysical properties and OLED performance. Adv. Funct. Mater. 26, 1813–1821 (2016)
Parker, C.A., Hatchard, C.G.: Triplet-singlet emission in fluid solutions. Phosphorescence of Eosin. Trans. Faraday Soc. 57, 1894–1904 (1961)
Penfold, T.J., Gindensperger, E., Daniel, C., Marian, C.M.: Spin-vibronic mechanism for intersystem crossing. Chem. Rev. 118, 6975–7025 (2018)
Pyykkö, P.: Relativistic effects in chemistry: more common than you thought. Annu. Rev. Phys. Chem. 63, 45–64 (2012)
Randall John Turton: The fluorescence of compounds containing manganese. Proc. r. Soc. Lond. A 170, 272–293 (1939)
Ravinson, D.S., Thompson, M.E.: Thermally assisted delayed fluorescence (TADF): fluorescence delayed is fluorescence denied. Mater. Horiz. 7(5), 1210–1217 (2020)
Reichardt, C.: Solvents and solvent effects: an introduction. Org. Process Res. Dev. 11, 105–113 (2007)
Rothe, C., Monkman, A.: Regarding the origin of the delayed fluorescence of conjugated polymers. J. Chem. Phys. 123, 1–6 (2005)
Santos, P.L., Ward, J.S., Data, P., Batsanov, A.S., Bryce, M.R., Dias, F.B., Monkman, A.P.: Engineering the singlet-triplet energy splitting in a TADF molecule. J. Mater. Chem. C 4, 3815–1824 (2016)
Sato, K., Shizu, K., Yoshimura, K., Kawada, A., Miyazaki, H., Adachi, C.: Organic luminescent molecule with energetically equivalent singlet and triplet excited states for organic light-emitting diodes. Phys. Rev. Lett. 110, 1–5 (2013)
Siddiqui, Q.T., Awasthi, A.A., Bhui, P., Muneer, M., Chandrakumar, K.R.S., Bose, S., Agarwal, N.: Thermally activated delayed fluorescence (Green) in undoped film and exciplex emission (Blue) in acridone-carbazole derivatives for OLEDs. J. Phys. Chem. C 123, 1003–1014 (2018)
Siddiqui, Q.T., Awasthi, A.A., Bhui, P., Parab, P., Muneer, M., Bose, S., Agarwal, N.: TADF and exciplex emission in a xanthone–carbazole derivative and tuning of its electroluminescence with applied voltage. RSC Adv. 9, 40248–40254 (2019)
Strickler, S.J., Berg, R.A.: Relationship between absorption intensity and fluorescence lifetime of molecules. J. Chem. Phys. 37, 814–822 (1962)
Sun, H., Hu, Z., Zhong, C., Chen, X., Sun, Z., Bredas, J.: Impact of dielectric constant on the singlet-triplet gap in thermally activated delayed fluorescence (TADF) materials impact of dielectric constant on the singlet-triplet gap in thermally activated delayed fluorescence materials. J. Phys. Chem. Lett. 8, 2393–2398 (2017)
Taneda, M., Shizu, K., Tanaka, H., Adachi, C.: High efficiency thermally activated delayed fluorescence based on 1 3 5-Tris(4-(Diphenylamino)Phenyl)-2 4 6-tricyanobenzene. Chem. Commun. 51, 5028–5031 (2015)
Uoyama, H., Goushi, K., Shizu, K., Nomura, H., Adachi, C.: Highly efficient organic light-emitting diodes from delayed fluorescence. Nature 492, 234–238 (2012)
Vikramaditya, T., Saisudhakar, M., Sumithra, K.: Computational study on thermally activated delayed fluorescence of donor-linker-acceptor network molecules. RSC Adv. 6, 37203–37211 (2016)
Wang, S., Yan, X., Cheng, Z., Zhang, H., Liu, Y., Wang, Y.: Highly efficient near-infrared delayed fluorescence organic light emitting diodes using a phenanthrene-based charge-transfer compound. Angew. Chemie Int. Ed. 54, 13068–13072 (2015)
Wang, K., Shi, Y.Z., Zheng, C.J., Liu, W., Liang, K., Li, X., Zhang, M., Lin, H., Tao, S.L., Lee, C.S., Ou, X.M., Zhang, X.H.: Control of dual conformations: developing thermally activated delayed fluorescence emitters for highly efficient single-emitter white organic light-emitting diodes. ACS Appl. Mater. Interfaces 10, 31515–31525 (2018)
Ward, J.S., Nobuyasu, R.S., Batsanov, A.S., Data, P., Monkman, A.P., Dias, F.B., Bryce, M.R.: The interplay of thermally activated delayed fluorescence (TADF) and room temperature organic phosphorescence in sterically-constrained donor-acceptor charge-transfer molecules. Chem. Commun. 52, 2612–2615 (2016)
Xie, F., Zhou, J., Li, Y.: Effects of the relative position and number of donors and acceptors on the properties of TADF materials. J. Mater. Chem. C 8(28), 9476–9494 (2020)
Xu, Y., Xu, P., Hu, D., Ma, Y.: Recent progress in hot exciton materials for organic light-emitting diodes. Chem. Soc. Rev. 50, 1030–1069 (2021)
Yang, Z., Mao, Z., Xie, Z., Zhang, Y., Liu, S., Zhao, J., Xu, J., Chi, Z., Aldred, M.P.: Recent advances in organic thermally activated delayed fluorescence materials. Chem. Soc. Rev. 46, 915–1016 (2017)
Youn Lee, S., Yasuda, T., Nomura, H., Adachi, C.: High-efficiency organic light-emitting diodes utilizing thermally activated delayed fluorescence from triazine-based donor-acceptor hybrid molecules. Appl. Phys. Lett. 101, 9–13 (2012)
Zhang, Q., Li, J., Shizu, K., Huang, S., Hirata, S., Miyazaki, H., Adachi, C.: Design of efficient thermally activated delayed fluorescence materials for pure blue organic light emitting diodes. J. Am. Chem. Soc. 134, 14706–14709 (2012)
Zhang, D., Cai, M., Zhang, Y., Zhang, D., Duan, L.: Sterically shielded blue thermally activated delayed fluorescence emitters with improved efficiency and stability. Mater. Horizons 3, 145–151 (2016)
Zhang, W., Song, H., Kong, J., Kuang, Z., Li, M., Guo, Q., Chen, C.F., Xia, A.: Importance of conformational change in excited states for efficient thermally activated delayed fluorescence. J. Phys. Chem. C 123, 19322–19332 (2019)
Zhang, X., Shi, Y., Cai, L., Zhou, Y., Wang, C.K., Lin, L.: Solvent effect on the photophysical properties of thermally activated delayed fluorescence molecules. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 225, 117473 (2020)
Zuehlsdorff, T.J., Isborn, C.M.: Modeling absorption spectra of molecules in solution. Int. J. Quantum Chem. 119, e25719 (2019)
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Behera, B.K., Agarwal, N. (2024). Thermally Activated Delayed Fluorescence in Metal-Free Small Organic Materials: Understanding and Applications in OLEDs. In: Ningthoujam, R.S., Tyagi, A.K. (eds) Handbook of Materials Science, Volume 1. Indian Institute of Metals Series. Springer, Singapore. https://doi.org/10.1007/978-981-99-7145-9_9
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