Excited state reversal in copper iodide clusters enables 100% exciton radiation

Article https://doi.org/10.1038/s41467-025-67664-x Excited state reversal in copper iodide clusters enables 100% exciton radiation Received: 26 May 2025 Accepted: 5 December 2025 1234567890():,; 1234567890():,; Check for updates Yushan Meng, Chenglin Liu, Jingjing Fei, Yue Xu, Yidan Wang, Jing Zhang, Chunbo Duan, Chunmiao Han & Hui Xu The non-radiative metallic core (MC) centered lowest excited states of most ligand-stabilized metallic clusters commonly quench radiative but high-lying ligand-centered excited states, e.g. intra-ligand charge transfer (LCT), which is one of the key issues limiting efficiencies of electroluminescent (EL) clusters. Herein, we realize the desired excited state reversal in a cubic [PXZDBFDP]2Cu4I4 (PXZDBFDP = 10-(4,6-bis(diphenylphosphino)dibenzo[b,d]furan-2-yl)−10H-phenoxazine) modified with strongly electrondonating phenoxazine (PXZ) to strengthen donor-acceptor (D-A) interactions and enhance LCT. Consequently, its thoroughly LCT-featured first singlet (S1) and triplet (T1) excited states are energetically lower than its Cu4I4-involved excited states. This case not only increases excited-state utilization through energy transfer from non-radiative MC to radiative LCT states, but also leads to balanced dual emission of thermally activated delayed fluorescence (TADF, 52%) and phosphorescence (PH, 48%) respectively from singlet and triplet LCT states. Therefore, compared to another congener [PhPXZDBFDP]2Cu4I4 (PhPXZDBFDP = 10-(4,6-bis(diphenylphosphino)dibenzo[b,d]furan-2-yl)−10Hphenylphenoxazine) with a D-π-A ligand and the normal low-lying MC states, [PXZDBFDP]2Cu4I4 achieves sevenfold increased photoluminescence quantum yield of ~90%, and the 13-fold increased maximum EL external quantum efficiency of 35.5%, which is the record-high value for EL homo-copper clusters. These results demonstrate the feasibility of accurate excited-state optimization for clusters through ligand engineering. In recent decades, cluster-based light-emitting diodes (CLED) emerge rapidly, extending the applications of this kind of materials into optoelectronic field1. Compared to other electroluminescent (EL) systems including organic molecules2–5, complexes6–8, polymers9–11, quantum dots12–15 and perovskites16–21, cluster emitters combine the merits of organic ligands and inorganic metallic cores (MC) with respect to optical performances and stabilities. Discrete energy levels of cluster molecules further make emission modulation flexible. But, they simultaneously exhibit complicated excited states composed of not only efficiently radiative high-lying ligand-centered (LC), e.g., metal/counterion-ligand charge transfer (Mn/XLCT), intraligand (LCT) and interligand charge transfer (ILCT) and locally excited (LE) states, but also low-lying cluster-center (CC) components including metalmetal (MMCT) and metal-counterion charge transfer (MXCT) inferior in radiation22. Obviously, the competition between LC and CC components in exciton allocation directly determines luminescent properties of cluster emitters, giving rise to a big challenge in performance improvement through rational excited-state modulation. Cuprous haloid clusters have the advantages of moderate Cu/Xligand interactions, tunable excited state compositions and MOE Key Laboratory of Functional Inorganic Material Chemistry, School of Chemistry and Material Science, Heilongjiang University, 74 Xuefu Road, e-mail: Harbin, China. Nature Communications | (2026)17:933 1 Article electrochemical stabilities, parts of whose merits for EL applications are already demonstrated by efficient organic light-emitting diodes based on CuX complexes23–26. Importantly, highly rigid and threedimensional CunXm structures can intrinsically and effectively alleviate structural relaxation at excited states, e.g., John-Teller distortion of Cu+ ions in mononuclear27–30 and binuclear rhomboidal Cu2X2 complexes31–33, and provide flexible platforms for accurately modulating MC-ligand interactions, therefore emerging rapidly as emitters for CLEDs in most recent years34. The excited states of CunXm clusters can be further modulated through: (i) MC optimization: geometric topologies and coordination environments of Cu+ ions can be modified to enhance molecular rigidities and adjust metal-metal/X and metal-ligand interactions, respectively reducing non-radiative energy loss and tuning ligand-MC charge transfer35–37. Consequently, chair-shape38, cubic39 and octahedral40,41 Cu4I4 and Cu4I642,43 with larger nuclei numbers, as well as heterobimetallic cores44, can enhance luminescence and improve efficiencies; (ii) Ligand engineering: functional modification of ligands can not only increase the ratios of LC components in excited states, but also influence metal-metal/X and MC-ligand interactions45. Our previous works demonstrated that introducing carbazole or acridine groups can effectively reduce the contributions of whole Cu4I4 cubic cores to excited states, leading to LC-predominant radiative excited states and photoluminescence (PL) quantum yields (PLQY, ηPL) reaching 90%46,47, but their half units, namely Cu2I2, were still involved in Mn/XLCT transitions. As a result, without external assistance, ϕEQE of CLEDs based on Cu4I4 cubes can hardly exceed 25%1,48. Actually, in most cases of clusters, one of the intrinsic issue is CC states energetically lower than LC states, therefore, it is difficult to completely prevent LC → CC energy transfer; meanwhile, the incorporation of Cu+ and I- in frontier molecular orbitals (FMO) inevitably induces the direct charge and exciton capture by Cu4I4 cores during EL processes. It means cluster involved charge transfer including not only CC states but also Mn/XLCT should be excluded from the lowest excited states, in turn making LCT and/or ILCT absolutely predominant in radiative transitions, which is the embodiment of the competition between MC and donor groups in intramolecular charge transfer to acceptor groups (Fig. 1a). However, it is undoubtedly a formidable challenge for thorough confinement of the lowest excited states and FMOs on organic ligands in low-valence metallic clusters. In this contribution, a donor-acceptor (D-A) type biphosphine ligand named PXZDBFDP is constructed as 4,6-bis(diphenyl-phosphaneyl)dibenzofuran (DBFDP) substituted with strongly electrondonating phenoxazine (PXZ) (Fig. 1a). The corresponding cubic [PXZDBFDP]2Cu4I4 successfully achieves thoroughly ligand-confined FMOs and the LCT-featured first singlet (S1) and triplet (T1) excited states with occupied and unoccupied orbitals respectively localized on PXZ and dibenzofuran (DBF); while, its Cu4I4 core reversely contributes to the high-lying S3 and T3 states. This case of abnormal excited state reversal makes non-radiative CC states of [PXZDBFDP]2Cu4I4 can be converted to its LCT state for radiation. Compared to [PhPXZDBFDP]2Cu4I4 with D-π-A type ligands and weakened LCT, the superiority of [PXZDBFDP]2Cu4I4 in radiation is demons (...truncated)