Intrinsic intermolecular photoinduced charge separation in organic radical semiconductors
Source abstract
Abstract
Abstract Organic radicals based on tris(2,4,6-trichlorophenyl)methyl (TTM) radicals show efficient photoluminescence from excitons in the spin-doublet manifold, but their potential in charge photogeneration remains unexplored. Here we report that when TTMs are in contact, photoexcitation generates TTM anion–TTM cation pairs. These can decay radiatively or be fully separated under an electric field bias. We use a triphenyl-substituted TTM (P 3 TTM) in which the phenyl end groups enhance intermolecular interactions. In dilute (5 wt%) films in a wide-energy-gap organic semiconductor host, we observe prompt photoluminescence from the excited radical at 645 nm, and a delayed component, beyond 1 μs, at 800 nm due to recombination of P 3 TTM anion–cation pairs. Measurements of photocurrent made with diode structures with 100% P 3 TTM showed close-to-unity charge collection efficiency in reverse bias. We have found ‘homojunction’ intermolecular charge separation, made possible when the extra energy for double occupancy of the non-bonding radical level on the anion is lower than the energy of the doublet exciton. This opens possibilities for light harvesting using single-material molecular semiconductors.
Source: crossref · Quality: baseline
Research context
OpenAlex topics: Organic Light-Emitting Diodes Research · Perovskite Materials and Applications · Luminescence and Fluorescent Materials
SciVX discovery tags are terminology-based. OpenAlex topics are source-provided classifications.
References (43)
Show source-provided references
1. Peng, Q., Obolda, A., Zhang, M. & Li, F. Organic light-emitting diodes using a neutral p radical as emitter: the emission from a doublet. Angew. Chem. Int. Ed. 54, 7091–7095 (2015).10.1002/anie.201500242 ↗
2. Ji, L., Shi, J., Wei, J., Yu, T. & Huang, W. Air-stable organic radicals: new-generation materials for flexible electronics?. Adv. Mater. 32, 1908015 (2020).10.1002/adma.201908015 ↗
3. Cui, X. et al. Stable π-radical nanoparticles as versatile photosensitizers for effective hypoxia-overcoming photodynamic therapy. Mater. Horiz. 8, 571–576 (2021).10.1039/D0MH01312A ↗
4. Gorgon, S. et al. Reversible spin-optical interface in luminescent organic radicals. Nature 620, 538–544 (2023).10.1038/s41586-023-06222-1 ↗
5. Ai, X. et al. Efficient radical-based light-emitting diodes with doublet emission. Nature 563, 536–540 (2018).10.1038/s41586-018-0695-9 ↗
6. Mayorga Burrezo, P. et al. Organic free radicals as circularly polarized luminescence emitters. Angew. Chem. Int. Ed. 58, 16282–16288 (2019).10.1002/anie.201909398 ↗
7. Mas-Torrent, M. et al. Organic radicals on surfaces: towards molecular spintronics. J. Mater. Chem. 19, 1691–1695 (2009).10.1039/B809875A ↗
8. Wu, S. et al. Toward two-dimensional π-conjugated covalent organic radical frameworks. Angew. Chem. Int. Ed. 57, 8007–8011 (2018).10.1002/anie.201801998 ↗
9. Gu, Q., Abdurahman, A., Friend, R. H. & Li, F. Polymer light emitting diodes with doublet emission. J. Phys. Chem. Lett. 11, 5638–5642 (2020).10.1021/acs.jpclett.0c01399 ↗
10. Teki, Y. Excited-state dynamics of non-luminescent and luminescent π-radicals. Chem. Eur. J. 26, 980–996 (2020).10.1002/chem.201903444 ↗
11. Murto, P. & Bronstein, H. Electro-optical π-radicals: design advances, applications and future perspectives. J. Mater. Chem. C 10, 7368–7403 (2022).10.1039/D1TC05268C ↗
12. Guo, H. et al. High stability and luminescence efficiency in donor–acceptor neutral radicals not following the Aufbau principle. Nat. Mater. 18, 977–984 (2019).10.1038/s41563-019-0433-1 ↗
13. Abdurahman, A. et al. Understanding the luminescent nature of organic radicals for efficient doublet emitters and pure-red light-emitting diodes. Nat. Mater. 19, 1224–1229 (2020).10.1038/s41563-020-0705-9 ↗
14. Cho, H.-H. et al. Efficient near-infrared organic light-emitting diodes with emission from spin doublet excitons. Nat. Photon. 18, 905–912 (2024).10.1038/s41566-024-01458-3 ↗
15. Lu, C. et al. Achieving nearly 100% photoluminescence quantum efficiency in organic radical emitters by fine-tuning the effective donor-acceptor distance. Adv. Funct. Mater. 34, 2314811 (2024).10.1002/adfm.202314811 ↗
16. Ghosh, P. et al. Decoupling excitons from high-frequency vibrations in organic molecules. Nature 629, 355–362 (2024).10.1038/s41586-024-07246-x ↗
17. Murto, P. et al. Mesitylated trityl radicals, a platform for doublet emission: symmetry breaking, charge-transfer states and conjugated polymers. Nat. Commun. 14, 4147 (2023).10.1038/s41467-023-39834-2 ↗
18. Murto, P. et al. Steric control of luminescence in phenyl-substituted trityl radicals. J. Am. Chem. Soc. 146, 13133–13141 (2024).10.1021/jacs.4c00292 ↗
19. Ohisa, S. & Honda, S. Luminescence enhancement by symmetry-breaking in the excited state in radical organic light-emitting diodes. Commun. Chem. 6, 238 (2023).10.1038/s42004-023-01039-5 ↗
20. Kimura, S. et al. Magnetoluminescence in a photostable, brightly luminescent organic radical in a rigid environment. Angew. Chem. Int. Ed. 57, 12727–12731 (2018).10.1002/anie.201806861 ↗
21. Mizuno, A., Matsuoka, R., Mibu, T. & Kusamoto, T. Luminescent radicals. Chem. Rev. 124, 1034–1121 (2024).10.1021/acs.chemrev.3c00613 ↗
22. Gu, Q. et al. Fast transfer of triplet to doublet excitons from organometallic host to organic radical semiconductors. Adv. Mater. 36, 2402790 (2024).10.1002/adma.202402790 ↗
23. Cho, H. H. et al. Near-infrared light-emitting diodes from organic radicals with charge control. Adv. Opt. Mater. 10, 2200628 (2022).10.1002/adom.202200628 ↗
24. Yadav, R. A. K., Dubey, D. K., Chen, S.-Z., Liang, T.-W. & Jou, J.-H. Role of molecular orbital energy levels in OLED performance. Sci. Rep. 10, 9915 (2020).10.1038/s41598-020-66946-2 ↗
25. Vasilopoulou, M. et al. High efficiency blue organic light-emitting diodes with below-bandgap electroluminescence. Nat. Commun. 12, 4868 (2021).10.1038/s41467-021-25135-z ↗
26. Kim, B. S. & Lee, J. Y. Engineering of mixed host for high external quantum efficiency above 25% in green thermally activated delayed fluorescence device. Adv. Funct. Mater. 24, 3970–3977 (2014).10.1002/adfm.201303730 ↗
27. Cho, H. H. et al. Efficient and bright organic radical light-emitting diodes with low efficiency roll-off. Adv. Mater. 35, 2303666 (2023).10.1002/adma.202303666 ↗
28. Walker, B. J., Musser, A. J., Beljonne, D. & Friend, R. H. Singlet exciton fission in solution. Nat. Chem. 5, 1019–1024 (2013).10.1038/nchem.1801 ↗
29. Kimura, S. et al. A ground-state-dominated magnetic field effect on the luminescence of stable organic radicals. Chem. Sci. 12, 2025–2029 (2021).10.1039/D0SC05965J ↗
30. Yu, C. P. et al. Near-infrared luminescent open-shell π-conjugated systems with a bright lowest-energy zwitterionic singlet excited state. Sci. Adv. 10, eado3476 (2024).10.1126/sciadv.ado3476 ↗
31. Zhou, Z. et al. Sulfone-functionalized Chichibabin’s hydrocarbons: stable diradicaloids with symmetry breaking charge transfer contributing to NIR emission beyond 900 nm. J. Am. Chem. Soc. 146, 6763–6772 (2024).10.1021/jacs.3c13270 ↗
32. Guo, J. et al. Novel triazine derivatives with deep LUMO energy levels as the electron-accepting components of exciplexes. J. Mater. Chem. C 9, 939–946 (2021).10.1039/D0TC04751A ↗
33. Halls, J. J., Pichler, K., Friend, R. H., Moratti, S. & Holmes, A. Exciton diffusion and dissociation in a poly(p-phenylenevinylene)/C60 heterojunction photovoltaic cell. Appl. Phys. Lett. 68, 3120–3122 (1996).10.1063/1.115797 ↗
34. Kaul, N. & Lomoth, R. The carbene cannibal: photoinduced symmetry-breaking charge separation in an Fe(III) N-heterocyclic carbene. J. Am. Chem. Soc. 143, 10816–10821 (2021).10.1021/jacs.1c03770 ↗
35. Ramirez, C. E. et al. Symmetry-breaking charge separation in the solid state: tetra(phenoxy)perylenediimide polycrystalline films. J. Am. Chem. Soc. 142, 18243–18250 (2020).10.1021/jacs.0c09185 ↗
36. Wega, J. & Vauthey, E. Bimolecular photoinduced symmetry-breaking charge separation of perylene in solution. Photochem. Photobiol. Sci. 23, 93–105 (2024).10.1007/s43630-023-00504-3 ↗
37. Markovic, V., Villamaina, D., Barabanov, I., Lawson Daku, L. M. & Vauthey, E. Photoinduced symmetry-breaking charge separation: the direction of the charge transfer. Angew. Chem. Int. Ed. 50, 7596–7598 (2011).10.1002/anie.201102601 ↗
38. Whited, M. T. et al. Symmetry-breaking intramolecular charge transfer in the excited state of meso-linked BODIPY dyads. Chem. Commun. 48, 284–286 (2012).10.1039/C1CC12260F ↗
39. Trinh, C. et al. Symmetry-breaking charge transfer of visible light absorbing systems: zinc dipyrrins. J. Phys. Chem. C 118, 21834–21845 (2014).10.1021/jp506855t ↗
40. Dong, Y. et al. Orientation dependent molecular electrostatics drives efficient charge generation in homojunction organic solar cells. Nat. Commun. 11, 4617 (2020).10.1038/s41467-020-18439-z ↗
41. Hirata, S. & Head-Gordon, M. Time-dependent density functional theory within the Tamm–Dancoff approximation. Chem. Phys. Lett. 314, 291–299 (1999).10.1016/S0009-2614(99)01149-5 ↗
42. Frisch, M. J. et al. Gaussian 16, Revision A.03 (Gaussian, Inc., 2016).
43. Refaely-Abramson, S. et al. Gap renormalization of molecular crystals from density-functional theory. Phys. Rev. B 88, 081204 (2013).10.1103/PhysRevB.88.081204 ↗