The development of high-performance near-infrared organic light-emitting diodes is hindered by strong non-radiative processes as governed by the energy gap law. Here, we show that exciton delocalization, which serves to decouple the exciton band from highly vibrational ladders in the S0 ground state, can bring substantial enhancements in the photoluminescence quantum yield of emitters, bypassing the energy gap law. Experimental proof is provided by the design and synthesis of a series of new Pt(ii) complexes with a delocalization length of 5–9 molecules that emit at 866–960 nm with a photoluminescence quantum yield of 5–12% in solid films. The corresponding near-infrared organic light-emitting diodes emit light with a 930 nm peak wavelength and a high external quantum efficiency up to 2.14% and a radiance of 41.6 W sr−1 m−2. Both theoretical and experimental results confirm the exciton–vibration decoupling strategy, which should be broadly applicable to other well-aligned molecular solids.
Subscribe to Journal
Get full journal access for 1 year
only $15.58 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
Caspar, J. V. & Meyer, T. J. Application of the energy gap law to nonradiative, excited-state decay. J. Phys. Chem. 87, 952–957 (1983).
Treadway, J. A. et al. Effect of delocalization and rigidity in the acceptor ligand on MLCT excited-state decay. Inorg. Chem. 35, 2242–2246 (1996).
Wilson, J. S. et al. The energy gap law for triplet states in Pt-containing conjugated polymers and monomers. J. Am. Chem. Soc. 123, 9412–9417 (2001).
Whittle, C. E., Weinstein, J. A., George, M. W. & Schanze, K. S. Photophysics of diimine platinum(ii) bis-acetylide complexes. Inorg. Chem. 40, 4053–4062 (2001).
Jelle, B. P., Kalnæs, S. E. & Gao, T. Low-emissivity materials for building applications: a state-of-the-art review and future research perspectives. Energy Buildings 96, 329–356 (2015).
Xiang, H., Cheng, J., Ma, X., Zhou, X. & Chruma, J. J. Near-infrared phosphorescence: materials and applications. Chem. Soc. Rev. 42, 6128–6185 (2013).
Tessler, N., Medvedev, V., Kazes, M., Kan, S. & Banin, U. Efficient near-infrared polymer nanocrystal light-emitting diodes. Science 295, 1506–1508 (2002).
Borek, C. et al. Highly efficient, near-infrared electrophosphorescence from a Pt–metalloporphyrin complex. Angew. Chem. Int. Ed. 46, 1109–1112 (2007).
Cocchi, M., Kalinowski, J., Virgili, D. & Williams, J. A. G. Excimer-based red/near-infrared organic light-emitting diodes with very high quantum efficiency. Appl. Phys. Lett. 92, 113302 (2008).
Graham, K. R. et al. Extended conjugation platinum(ii) porphyrins for use in near-infrared emitting organic light emitting diodes. Chem. Mater. 23, 5305–5312 (2011).
Barbieri, A., Bandini, E., Monti, F., Praveen, V. K. & Armaroli, N. The rise of near-infrared emitters: organic dyes, porphyrinoids and transition metal complexes. Top. Curr. Chem. 374, 47 (2016).
Ai, X. et al. Efficient radical-based light-emitting diodes with doublet emission. Nature 563, 536–540 (2018).
Zhang, Y. et al. Near-infrared emitting materials via harvesting triplet excitons: molecular design, properties and application in organic light emitting diodes. Adv. Opt. Mater. 6, 1800466 (2018).
Özçelik, S. & Akins, D. L. Superradiance of aggregated thiacarbocyanine molecules. J. Phys. Chem. B 103, 8926–8929 (1999).
Arias, D. H. et al. Thermally-limited exciton delocalization in superradiant molecular aggregates. J. Phys. Chem. B 117, 4553–4559 (2013).
Cai, K., Xie, J. & Zhao, D. NIR J-aggregates of hydroazaheptacene tetraimides. J. Am. Chem. Soc. 136, 28–31 (2014).
Qian, G. et al. Simple and efficient near-infrared organic chromophores for light-emitting diodes with single electroluminescent emission above 1,000 nm. Adv. Mater. 21, 111–116 (2009).
Zampetti, A., Minotto, A. & Cacialli, F. Near-infrared (NIR) organic light-emitting diodes (OLEDs): challenges and opportunities. Adv. Funct. Mater. 29, 1807623 (2019).
Klaus, D. R., Keene, M., Silchenko, S., Berezin, M. & Gerasimchuk, N. 1D polymeric platinum cyanoximate: a strategy toward luminescence in the near-infrared region beyond 1,000 nm. Inorg. Chem. 54, 1890–1900 (2015).
Ly, K. T. et al. Near-infrared organic light-emitting diodes with very high external quantum efficiency and radiance. Nat. Photon. 11, 63–68 (2017).
Zhang, Y. et al. Achieving NIR emission for donor–acceptor type platinum(ii) complexes by adjusting coordination position with isomeric ligands. Inorg. Chem. 57, 14208–14217 (2018).
Yam, V. W.-W., Wong, K. M.-C. & Zhu, N. Solvent-induced aggregation through metal···metal/π···π interactions: large solvatochromism of luminescent organoplatinum(ii) terpyridyl complexes. J. Am. Chem. Soc. 124, 6506–6507 (2002).
Yu, C., Wong, K. M.-C., Chan, K. H.-Y. & Yam, V. W.-W. Polymer-induced self-assembly of alkynylplatinum(ii) terpyridyl complexes by metal–metal/pi–pi interactions. Angew. Chem. Int. Ed. 44, 791–794 (2005).
Wong, K. M.-C. & Yam, V. W.-W. Self-assembly of luminescent alkynylplatinum(ii) terpyridyl complexes: modulation of photophysical properties through aggregation behavior. Acc. Chem. Res. 44, 424–434 (2011).
Hong, Y., Lam, J. W. Y. & Tang, B. Z. Aggregation-induced emission. Chem. Soc. Rev. 40, 5361–5388 (2011).
Englman, R. & Jortner, J. The energy gap law for radiationless transitions in large molecules. Mol. Phys. 18, 145–164 (1970).
Herrera, F. & Spano, F. C. Cavity-controlled chemistry in molecular ensembles. Phys. Rev. Lett. 116, 238301 (2016).
Spano, F. C., Silvestri, L., Spearman, P., Raimondo, L. & Tavazzi, S. Reclassifying exciton–phonon coupling in molecular aggregates: evidence of strong nonadiabatic coupling in oligothiophene crystals. J. Chem. Phys. 127, 184703 (2007).
Spano, F. C. The spectral signatures of Frenkel polarons in H- and J-aggregates. Acc. Chem. Res. 43, 429–439 (2010).
Spano, F. C. & Yamagata, H. Vibronic coupling in J-aggregates and beyond: a direct means of determining the exciton coherence length from the photoluminescence spectrum. J. Phys. Chem. B 115, 5133–5143 (2011).
Chen, W.-C., Chou, P.-T. & Cheng, Y.-C. Low internal reorganization energy of the metal–metal-to-ligand charge transfer emission in dimeric Pt(ii) complexes. J. Phys. Chem. C 123, 10225–10236 (2019).
Hestand, N. J. & Spano, F. C. Interference between Coulombic and CT-mediated couplings in molecular aggregates: H- to J-aggregate transformation in perylene-based π-stacks. J. Chem. Phys. 143, 244707 (2015).
Yersin, H., Rausch, A. F., Czerwieniec, R., Hofbeck, T. & Fischer, T. The triplet state of organo-transition metal compounds. Triplet harvesting and singlet harvesting for efficient OLEDs. Coord. Chem. Rev. 255, 2622–2652 (2011).
Li, K. et al. Highly phosphorescent platinum(ii) emitters: photophysics, materials and biological applications. Chem. Sci. 7, 1653–1673 (2016).
Hutchison, G. R., Ratner, M. A. & Marks, T. J. Hopping transport in conductive heterocyclic oligomers: reorganization energies and substituent effects. J. Am. Chem. Soc. 127, 2339–2350 (2005).
Robinson, G. W. & Frosch, R. P. Electronic excitation transfer and relaxation. J. Phys. Chem. 38, 1187–1203 (1963).
Wysokiński, R., Hernik, K., Szostak, R. & Michalska, D. Electronic structure and vibrational spectra of cis-diammine(orotato)platinum(ii), a potential cisplatin analogue: DFT and experimental study. Chem. Phys. 333, 37–48 (2007).
Juliá, F. & González-Herrero, P. Aromatic C–H activation in the triplet excited state of cyclometalated platinum(ii) complexes using visible light. J. Am. Chem. Soc. 138, 5276–5282 (2016).
Podeszwa, R., Bukowski, R. & Szalewicz, K. Potential energy surface for the benzene dimer and perturbational analysis of π–π interactions. J. Phys. Chem. A 110, 10345–10354 (2006).
Pullerits, T., Chachisvilis, M. & Sundström, V. Exciton delocalization length in the B850 antenna of Rhodobacter sphaeroides. J. Phys. Chem. 100, 10787–10792 (1996).
Chesnut, D. B. & Suna, A. Fermion behavior of one‐dimensional excitons. J. Chem. Phys. 39, 146–149 (1963).
van Burgel, M., Wiersma, D. A. & Duppen, K. The dynamics of one‐dimensional excitons in liquids. J. Chem. Phys. 102, 20–33 (1995).
Kim, K.-H. et al. Crystal organic light-emitting diodes with perfectly oriented non-doped Pt-based emitting layer. Adv. Mater. 28, 2526–2532 (2016).
Sommer, J. R. et al. Efficient near-infrared polymer and organic light-emitting diodes based on electrophosphorescence from (tetraphenyltetranaphtho[2,3]porphyrin)platinum(ii). ACS Appl. Mater. Interfaces 1, 274–278 (2009).
Nagata, R., Nakanotani, H. & Adachi, C. Near-infrared electrophosphorescence up to 1.1 µm using a thermally activated delayed fluorescence molecule as triplet sensitizer. Adv. Mater. 29, 1604265 (2017).
Kim, D.-H. et al. High-efficiency electroluminescence and amplified spontaneous emission from a thermally activated delayed fluorescent near-infrared emitter. Nat. Photon. 12, 98–104 (2018).
Minotto, A. et al. Efficient near-infrared electroluminescence at 840 nm with ‘metal-free’ small-molecule:polymer blends. Adv. Mater. 30, 1706584 (2018).
Chang, C.-H. et al. A new class of sky-blue-emitting Ir(iii) phosphors assembled using fluorine-free pyridyl pyrimidine cyclometalates: application toward high-performance sky-blue- and white-emitting OLEDs. ACS Appl. Mater. Interfaces 5, 7341–7351 (2013).
Liu, X. et al. Syntheses, crystal structure and photophysical property of iridium complexes with 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives as ancillary ligands. J. Organomet. Chem. 785, 11–18 (2015).
This research was supported by funding from the Ministry of Science and Technology (MOST), the Featured Areas Research Program within the framework of the Higher Education Sprout Project administered by the Ministry of Education (MOE), National Taiwan University, Soochow University and the Research Grant Council and City University of Hong Kong. We are also grateful to the National Center for High-Performance Computing (NCHC) and National Synchrotron Radiation Research Center (NSRRC) for computer time and facilities, respectively.
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Wei, Y., Wang, S.F., Hu, Y. et al. Overcoming the energy gap law in near-infrared OLEDs by exciton–vibration decoupling. Nat. Photonics (2020). https://doi.org/10.1038/s41566-020-0653-6