Abstract
Advanced photonic materials showing two-photon absorption (2PA) have been widely explored to develop three-dimensional imaging, micro and nanofabrication, all-optical switching, lithography on a nanoscale and many other enabling technologies. These all require nonlinear absorption chromophores with intrinsic 2PA cross-sections and long-term photo- and thermal stability. Here, we disclose the very first example of the dipolar carbene-metal-amide (CMA) material showing a enhanced 2PA cross-section up to 105 GM. Overall molecular design considerations such as extended π-conjugation (to increase polarizability), minimizing the singlet-triplet energy gap (ΔEST), and using heavy metal atoms are the first design principles to obtain bright one- and two-photon excited thermally activated delayed fluorescence (TADF) material, showing one of the highest radiative rate of 2.18·106 s-1 across CMA materials. Bright red CMA 2P-TADF material shows excellent photostability (LT50 = 3 h) to 20 mW femtosecond pulsed laser excitation at 1000 nm, encouraging further CMA exploration for future applications in advanced photonic technologies requiring third-order nonlinear optical properties.
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Acknowledgements
A.S.R. acknowledges support from the Royal Society (grant nos. URF\R1\180288, RGF\EA\181008, URF\R\231014), EPSRC (grant code EP/K039547/1 and APP46952). M.L. acknowledges the Academy of Finland Flagship Programme, Photonics Research and Innovation (PREIN), decision 320166, the Finnish Grid and Cloud Infrastructure resources (urn:nbn:fi:research-infras-2016072533). N.L.P. acknowledges the Doctoral Programme in Science, Forestry and Technology (Lumeto, University of Eastern Finland). T.N.R. is a postdoctoral researcher of the Fonds de la Recherche Scientifique – FNRS” (F.R.S.–FNRS). We thank Dr Louise Natrajan, EPSRC and University of Manchester for access the Centre for Radiochemistry Research National Nuclear User’s Facility (NNUF, EP/T011289/1) to use FLS-1000 fluorometer. D.T.W.T. acknowledges Diamond Light Source for access to the DL-SAXS equipment (experiment number SM40538-1) supported by an EPSRC grant (EP/R042683/1), and instrument scientist Dr Paul Wady for their help and support during beamtime. L.M. thanks the Winton Programme and Harding Distinguished Postgraduate Scholarship for funding. A.J.G. thanks the Leverhulme Trust for an Early Career Fellowship (ECF-2022-445), the Knut and Alice Wallenberg Foundation for a Wallenberg Academy Fellows award (KAW 2023.0082), and the Swedish Research Council (VR) for a Starting Grant (2024-03915). European Union’s Horizon 2020 research and innovation programme grant agreement no. 101020167 (L.M. and A.J.G.).
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I.D.N. carried out synthesis and characterization, electrochemistry, UV-vis and photoluminescence spectroscopy and analysis, L.M. and A.J.G. performed transient absorption measurements and analysis, D.T.W.T. performed GIWAXS measurements and analysis, T.N.R., N.L.P., G.L., M.L., Y.O. performed theoretical calculations for the ground and excited states and calculations involving a two-photon process, C.T.S. assisted with initial collection of the two-photon absorption data and performed two-photon excited TADF lifetime measurements, G.F.S.W. performed single crystal experiment and refinement, M.B.-D., J.D. and I.D.N. performed two-photon absorption and luminescence experiments in fluid and solid state, A.S.R. conceived and designed the idea. J.D., M.L., Y.O. and A.S.R. planned the project and designed the experiments. I.D.N., Y.O., and A.S.R. wrote the manuscript. All authors contributed to the discussion of the results, analysis of the data, and reviewed and corrected the manuscript.
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Nwosu, I.D., Matasović, L., Ramos, T.N. et al. Enhanced third-order optical nonlinearity in a dipolar carbene-metal-amide material with two-photon excited delayed fluorescence. Commun Chem (2026). https://doi.org/10.1038/s42004-026-01928-5
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DOI: https://doi.org/10.1038/s42004-026-01928-5
