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

Domain: physics
Published: 2025-12-16
Editorial outcome: minor_revision

Abstract
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 electron-donating 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)−10H-phenylphenoxazine) 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.

Introduction
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 metal-metal (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/X-ligand interactions, tunable excited state compositions and 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 three-dimensional Cu4X4 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 Cu4I4 42,43 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 electron-donating 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 demonstrated with its fourfold larger singlet oscillator strength (fS) and sevenfold increased ϕPL to ~90%. [PXZDBFDP]2Cu4I4 further reveals the advantage in suppressing exciton accumulation induced quenching, since its LCT-featured S1 and T1 excited states support thermal equilibrium between intersystem crossing (ISC) and reverse ISC, giving rise to balanced dual emission with a thermally activated delayed fluorescence (TADF)/phosphorescence (PH) ratio of 52/48. Consequently, [PXZDBFDP]2Cu4I4 endowed its devices with 180-fold increased ηEQE beyond 35%, which is the record-high value for EL homo-copper clusters. These results demonstrate the feasibility of accurate excited-state optimization for cluster molecules through ligand engineering strategy.

Results
Cluster design and structures
A chelating motif DBFDP is used to form the cubic MC skeleton, namely [DBFDP]2Cu4I4 39. P→CuI coordination leads to Mn/XLCT from Cu4I4 to DBFDP under excitation, in which DBF actually serves as acceptor group withdrawing electron from Cu+. In this sense, LCT and ILCT components in LC excited states, involve in DBF as acceptor identical to that in Mn/XLCT, rendering the competition between them with respect to exciton allocation, let alone MMCT and MXCT in CC states. Obviously, donor substituents on DBFDP can enhance LCT and ILCT with DBF, in turn weakening MC-involved charge transfer (Fig. 1a). If the electron-donating effects of donor groups stronger than Cu4I4, it is of possibility to make LCT and/or ILCT energetically lower than CC states, leading to the reverse CC→LC energy transfer opposite to the common situations of Cu4I4 clusters, therefore making all the energies can be utilized through LCT/ILCT radiation. With this consideration, PXZ with accumulated electron-donating conjugation effects from O and N atoms can be competent as donor to strengthen interactions with DBF for the maximum. To evaluate the sensitivity of excited-state characteristics on electronic configurations of ligands, we designed two ligands PXZDBFDP and PhPXZDBFDP respectively having D-A and D-π-A structures for comparison. Obviously, D-A interactions between PXZ and DBF in PhPXZDBFDP is reduced by its phenylene as a π-linker, in turn enhancing MC-involved charge transfer.

PXZDBFDP and PhPXZDBFDP can be readily synthesized through Ullman and Suzuki coupling reactions with yields more than 80%, and then used to prepare Cu4I4 cubes with CuI in dichloromethane (Supplementary Figs 1–19). In contrast to the symmetric coordination skeleton of [PhPXZDBFDP]2Cu4I4, P-Cu bonds on the same sides of PXZ in [PXZDBFDP]2Cu4I4 are shorter than those on the other sides, accompanied by its slightly asymmetric Cu4I4 core, because the stronger electron-donating effect of PXZ on DBFDP unit increases electron cloud density of the P atom on the same side of PXZDBFDP (Fig. 1b and Supplementary Fig. 20 and Supplementary Table 1–4). Furthermore, for [PhPXZDBFDP]2Cu4I4, its phenylene and DBF groups are basically coplanar, inevitably inducing FMO extension and overlapping. On the contrary, PXZ groups in [PXZDBFDP]2Cu4I4 are almost orthogonal to DBF moieties, evidenced by their dihedral angles more than 70o, which can render FMO separation for PXZDBFDP, thereby enhancing PXZ→DBF charge transfer.

Density function theory (DFT) simulation on ground states (S0) of these two clusters shows their first three unoccupied molecular orbitals and highest occupied molecular orbitals (HOMO) are localized on DBF and PXZ groups, respectively (Fig. 1c and Supplementary Fig. 21). On the contrary to the situation of [PhPXZDBFDP]2Cu4I4, the HOMO-1 and HOMO-2 of [PXZDBFDP]2Cu4I4 are respectively contributed by PXZ and Cu4I4 core, reflecting the stronger D-A interactions. Consequently, [PXZDBFDP]2Cu4I4 exhibits the shallower HOMO and deeper lowest unoccupied molecular orbital (LUMO), compared to [PhPXZDBFDP]2Cu4I4, which are consistent with the HOMO and LUMO energy levels of −5.46 and −3.01 eV and −5.50 and −2.84 eV experimentally estimated with cyclic voltammetry (CV) analysis (Supplementary Figs 22 and 23 and Supplementary Table 5). Furthermore, the energy gap between the highest occupied molecular orbitals on PXZ and Cu4I4 core is 0.163 eV for [PXZDBFDP]2Cu4I4 (HOMO→HOMO-2), which is more than doubled in comparison to that of [PhPXZDBFDP]2Cu4I4 (HOMO→HOMO-1). In contrast to [PXZDBFDP]2Cu4I4, PXZ of [PXZDBFDP]2Cu4I4 is superior to Cu4I4 core with respect to electron donating effect, in addition to its stronger PXZ→DBF charge transfer.

Natural transition orbital (NTO) analysis on S0→S1 and S0→T1 excitations of [PXZDBFDP]2Cu4I4 and [PhPXZDBFDP]2Cu4I4 reveals their opposite excited-state locations (Fig. 1c and Supplementary Figs 24 and 25). The “holes” and “electrons” of the S1 and T1 states for [PhPXZDBFDP]2Cu4I4 are respectively localized on Cu4I4 core and DBF groups, corresponding to Mn/XLCT and CC states, which are identical to those of [DBFDP]2Cu4I4. Its lowest excited state involved in PXZ is the T6 state, whose “hole” and “electron” are localized on PXZ and dispersed on PXZ, DBF and phenylene, respectively, to form a hybrid “charge transfer + locally excited” state. On the contrary, the strong PXZ-DBF charge transfer in [PXZDBFDP]2Cu4I4 induces excited state reversal that its S1 and T1 states featuring LCT states with “holes” and “electrons” respectively localized on PXZ and DBF; while, its Cu4I4 core and DBF make the major contributions to “holes” and “electrons” of the S3 and T3 states characteristic of Mn/XLCT and CC states. Obviously, the HOMOs and LUMOs localized on PXZ and DBF groups make the ligands predominant in carrier injection during EL processes. However, the energy transfer from the high-lying LCT states of [PhPXZDBFDP]2Cu4I4 to its lowest CC states worsen the exciton quenching by the latter. The superiority of the LCT-featured S1 state for [PXZDBFDP]2Cu4I4 in radiation is directly verified by its oscillator strength (fS) more than three folds of its high-lying CC-featured S3 state, and four folds of that of CC-featured S1 state for [PhPXZDBFDP]2Cu4I4. More importantly, CC states of [PXZDBFDP]2Cu4I4 are ~0.25 eV higher than its LCT-featured S1 and T1 states, leading to abnormal “reverse” energy transfer from non-radiative CC to radiative LCT states. In this case, it is convincing that [PXZDBFDP]2Cu4I4 can theoretically harvest 100% electro-generated excitons confined on both ligands and MC for emission, therefore breaking through the efficiency bottleneck for EL copper clusters.

Photophysical properties
π→π* and n→π* transitions of the ligands peaked at ~240 and 280 nm are predominant in electronic absorption spectra of the clusters in dilute solutions (10−6 M in CH2Cl2), accompanied by long charge transfer absorption tails at 300–480 nm (Fig. 2a and Supplementary Table 1). In absorption spectra of spin-coated neat films, besides ligands-attributed bands, intermolecular interactions markedly enhance the charge transfer bands (Supplementary Fig. 26 and Supplementary Table 5). Nonetheless, it can be noted that CC band at 350–400 nm is predominant for [PhPXZDBFDP]2Cu4I4, but [PXZDBFDP]2Cu4I4 exhibits more distinct LCT band at 350–450 nm. Furthermore, excitation spectra of the neat films show the predominant contributions of MLCT, CC and LCT states to emission, which is consistent with NTO analysis results. [PXZDBFDP]2Cu4I4 and [PhPXZDBFDP]2Cu4I4 reveal the similar MLCT bands peaked at ~320 and 335 nm, accompanied with CC bands as shoulder peaks at ~340 and 370 nm, respectively. Importantly, in opposite to high-energy LCT band of [PhPXZDBFDP]2Cu4I4 at 275 nm, LCT band of neat [PXZDBFDP]2Cu4I4 film is the lowest energy band peaked at ~400 nm, experimentally demonstrating the abnormal excited-state reversal and the resulted exothermic CC→LCT energy transfer through fast and efficient internal conversion.

PL spectrum of neat [PXZDBFDP]2Cu4I4 film is composed of a single-peak emission at 520 nm originated from LCT radiation (Fig. 2a and Supplementary Table 5). In contrast, neat [PhPXZDBFDP]2Cu4I4 film reveal two emission peaks at 522 and 626 nm originated from its high-energy MLCT and low-energy CC states with different geometrical reorganization (Supplementary Fig. 27)49,50, which is similar to donor-free [DBFDP]2Cu4I4 in accord with their identical CC-featured S1 and T1 states22,39. After 20% dispersed in bis-4-(N-carbazolyl)phenyl) phenylphosphine oxide (BCPO) matrix, the emission of [PXZDBFDP]2Cu4I4 is slightly blue-shifted to 508 nm, due to reduced inter-ligand interactions between adjacent cluster molecules. PL spectrum of BCPO:20% [PhPXZDBFDP]2Cu4I4 film is more markedly changed to single-peak emission at 498 nm, accompanied by a CC tail in 600–700 nm, because of suppressed quenching on MLCT state induced by inter-ligand interactions and lower radiative possibility for CC than MLCT.

On the basis of time-resolved technology, the nominal prompt (PF) and delayed fluorescence (DF) and PH spectra of BCPO:20% [PXZDBFDP]2Cu4I4 are similar but still gradually and slightly red shifted, different to completely overlapped spectra of [PhPXZDBFDP]2Cu4I4. According to absorption edges and 0–0 transitions of time-resolved PH spectra recorded after a delay of 200 µs, the S1 and T1 energy levels of [PXZDBFDP]2Cu4I4 and [PhPXZDBFDP]2Cu4I4 are 2.82 and 2.78 eV, and 2.90 and 2.88 eV, corresponding to singlet-triplet splitting energies (ΔEST) of 0.04 and 0.02 eV, respectively, which are highly consistent with NTO results (Supplementary Table 5). Compared to neat films, time decays of BCPO:20% cluster films are also markedly elongated, owing to suppressed quenching (Fig. 2b). Nonetheless, [PXZDBFDP]2Cu4I4 doped films reveal markedly shorter lifetimes, which are beneficial to reduce collisional quenching. For the same reason, their lifetime dependence on doping concentration is limited. In contrast, lifetime of [PhPXZDBFDP]2Cu4I4 in BCPO matrix is elongated by about three folds, indicating its fragile excited states highly sensitive to quenching effect. Consequently, BCPO:x% [PXZDBFDP]2Cu4I4 films achieve markedly higher ϕPL reaching 90% at x=20 for the maximum; while, ϕPL of [PhPXZDBFDP]2Cu4I4 based analogs also reaches the maximum value at x=20 but as low as ~11%, which is only about one eighth of that of BCPO:20% [PXZDBFDP]2Cu4I4.

PL spectra of [PXZDBFDP]2Cu4I4 in film are almost unchanged in the temperature range of 20-300 K, further evidencing the radiation from single-component nLCT states (n=1 and 3 for singlet and triplet, Supplementary Fig. 7a). In contrast, the intensities of CC-attributed long-wavelength bands for [PhPXZDBFDP]2Cu4I4 film are directly proportional to temperature, which is consistent with previously reported thermochromic copper iodide clusters, and commonly ascribed to MLCT→CC energy transfer through thermal relaxation (Supplementary Fig. 27b)51,52. Furthermore, although collisional quenching of neat [PhPXZDBFDP]2Cu4I4 film is worsened by increasing temperature and therefore induces gradually decrease of lifetime, with suppressed inter-cluster interactions, lifetime of BCPO:20% [PhPXZDBFDP]2Cu4I4 becomes directly proportional to temperature, in accord to the conversion from partially forbidden 3MLCT to forbidden 3CC state with smaller radiative rate constant (Supplementary Fig. 28). On the contrary, time decays of both neat and 20% doped films of [PXZDBFDP]2Cu4I4 are in reverse proportion to temperature (Supplementary Fig. 29). Considering its emission from single-component nLCT states, the lifetime decrease for [PXZDBFDP]2Cu4I4 verifies the gradual transition from forbidden 3LCT-attributed PH at low temperature to allowed 1LCT-attributed TADF at high temperature.

The PH/TADF ratios of the emissions from the clusters are quantitatively evaluated with the fractional PH and TADF intensities as functions of temperature, respectively (please see details in supporting information) (Fig. 2c)53. In consistence with NTO results, [PhPXZDBFDP]2Cu4I4 reveals pure PH emission with the nearly temperature-independent ratios more than 99%, which further manifests the elongated lifetime at high temperature is due to conversion between two triplet states, namely 3MLCT→3CC through thermal relaxation54–56. On the contrary, despite ~100% PH at <50 K, TADF intensities for [PXZDBFDP]2Cu4I4 rapidly increase at higher temperature, in accord with the thermal activation mechanism for triplet→singlet conversion. The balanced temperature at equal TADF and PH ratios of 50% is ~280 K. At ambient temperature, TADF proportion only slightly increases to 52%. In this sense, both the singlet and triplet LCT states of [PXZDBFDP]2Cu4I4 nearly equally contribute to PH and TADF under a dual-emission mode, which can simultaneously reduce exciton-accumulation induced quenching and accelerate radiation.

Temperature-dependent time-resolved emission (TRES) spectra of BCPO:x% [PXZDBFDP]2Cu4I4 (x=100 for neat film, and 20) reveal that emissions become concentrated, along with temperature increasing (Fig. 2d and Supplementary Fig. 30a). This variation tendency can be attributed to the accelerated radiation through both nLCT channels, especially the singlet one. The same situation for the neat film further indicates that the increased contribution of 1LCT state to radiation effectively alleviates the triplet quenching. TRES spectra of neat [PhPXZDBFDP]2Cu4I4 film show that the emissions are elongated when increasing temperature from 50 to 200 K, and then shortened at 300 K, corresponding to a transition to forbidden CC state in the first stage and CC quenching at the second stage (Fig. 2d and Supplementary Figs 30b and 31). BCPO matrix alleviates quenching of [PXZDBFDP]2Cu4I4, but transition from 3MLCT to 3CC still render the emission elongation, due to slowed radiation from the latter.

It is convincing that the state-of-the-art ϕPL values of BCPO:x% [PXZDBFDP]2Cu4I4 films are ascribed to the radiative LCT-featured S1 and T1 states, reversed CC→LCT energy transfer and the balanced dual emission, giving rise to effective radiation acceleration and quenching suppression. Furthermore, with exciton state reversal, the direct carrier capture by MC of [PXZDBFDP]2Cu4I4 during EL process can not reduce the exciton utilization efficiencies, since carrier recombination on its MC would be followed with CC→LCT exciton transfer.

EL properties
Encouraged by its ϕPL of 90% and dual-emissive characteristics, we used [PXZDBFDP]2Cu4I4 and [PhPXZDBFDP]2Cu4I4 as dopants in emitting layers (EML) of BCPO:x% clusters to fabricate spin-coated CLEDs with bilayer structures (Fig. 3a). With the shallower HOMOs and deeper LUMOs and lower S1 and T1 energy levels than those of BCPO hosts, the clusters can effectively confine the electro-generated excitons through both direct carrier capture and energy transfer. Therefore, despite the optimal x of 20 for the highest EL performances, all the devices exhibited green and yellowish green emissions from the clusters peaked at ~510 nm (Fig. 3b, and Supplementary Figs 32–33 and Supplementary Table 6). Nevertheless, profiles of EL spectra for [PXZDBFDP]2Cu4I4 based devices are markedly narrower than those of analogs based on [PhPXZDBFDP]2Cu4I4 by ~50 nm with respect to full width at half maximum (FWHM).

Owing to its stronger carrier injecting ability, [PXZDBFDP]2Cu4I4 effectively reduced driving voltages of its devices by 0.1–0.5 V for turn-on and 1.5–3.7 V at 100 cd m−2, in comparison to [PhPXZDBFDP]2Cu4I4 based analogs (Fig. 3c, Supplementary Figs 32–33 and Supplementary Table 6). Despite their comparable current densities (J), the maximum luminance of [PXZDBFDP]2Cu4I4 based devices was beyond 1500 nits, which was markedly increased by ten folds, compared to [PhPXZDBFDP]2Cu4I4 based analogs. Considering the similar J for these devices, the larger luminance of the former reflects the stronger exciton utilization ability of [PXZDBFDP]2Cu4I4 during EL process. Inspiringly, BCPO:20% [PXZDBFDP]2Cu4I4 achieved the the state-of-the-art efficiencies with the maxima as high as 95.9 cd A−1 for current efficiency (CE, ηCE), 75.3 lm W−1 for power efficiency (PE, ηPE) and 35.5% for ηEQE, respectively (Fig. 3d, Supplementary Figs 32–33 and Supplementary Table 6), which dramatically improve the efficiency record of CLEDs based on copper clusters by about one fifth57. Actually, [PXZDBFDP]2Cu4I4 is one of the only two clusters reported so far can realize the maximum ηEQE beyond 35% (Fig. 3e and Supplementary Table 3). It is noteworthy that compared to the other one with sharply decreased ηEQE of ~10% at 500 nits, [PXZDBFDP]2Cu4I4 is more superior in efficiency stability at high luminance, evidenced by its ηEQE remaining 32.4% and 25.0% at 100 and 500 nits, corresponding to markedly reduced EQE roll-offs of 8.7% and 29.6%. It is noteworthy that EL efficiencies of [PXZDBFDP]2Cu4I4 are one order of magnitude larger than those of [PhPXZDBFDP]2Cu4I4 based analogs. At x=20, the maximum ηEQE of the latter was only 2.7% at the same level of donor-free parent cluster [DBFDP]2Cu4I4 39, which is as low as one thirteenth of that of [PXZDBFDP]2Cu4I4 based devices.

Taking out-coupling ratio of indium tin oxide (ITO) glass as 0.30, [PXZDBFDP]2Cu4I4 based devices achieved 100% internal quantum (IQE, ηIQE) and exciton utilization efficiencies (EUE, ηEUE). It is noticed that ηEQE differences between these two clusters are about 1.6 folds of those between their ϕPL. Obviously, during EL process, MC-involved excited states of [PhPXZDBFDP]2Cu4I4 worsened exciton quenching through direct carrier capture; while, the reversed CC and LCT energy levels make highly radiative LCT-featured S1 and T1 states of [PXZDBFDP]2Cu4I4 can harvest 100% excitons generated on both ligands and Cu4I4 core. Furthermore, single-emission mode based on the triplet state of [PhPXZDBFDP]2Cu4I4 worsened triplet-triplet annihilation and triplet-polaron quenching. On the contrary, the balanced dual emissions from [PXZDBFDP]2Cu4I4 effectively alleviated exciton accumulation induced quenching at high luminance, therefore limiting efficiency roll-offs.

The different exciton kinetics in PL and EL processes were investigated with steady-state and time-resolved PL and EL spectra (Fig. 4a). BCPO:20% [PXZDBFDP]2Cu4I4 reveals identical PL and EL spectra with the same peak wavelengths and FWHM values. In this case, the composition and ratio of excited states incorporated in PL and EL of [PhPXZDBFDP]2Cu4I4 should be consistent, namely desired balanced radiations from nLCT states. On the contrary, EL peak of BCPO:20% [PhPXZDBFDP]2Cu4I4 are red shifted, in comparison to the PL spectra. More notably, its EL FWHM of 141 nm is about 1.5 folds of the PL value as 93 nm. Through dual-peak fitting, it is clear that different to photo-excitation, because of the statistical majority of electro-generated triplet excitons, the population of 3CC state for [PhPXZDBFDP]2Cu4I4 is markedly increased in EL process, rendering markedly enhanced long-wavelength emission and thereby worsening exciton quenching39. EL decays of BCPO:20% [PhPXZDBFDP]2Cu4I4 were elongated by at least one order of magnitude, in comparison to its PL decays (Fig. 4a and Supplementary Fig. 34). Obviously, besides exciton diffusion in the devices, largely decelerated exciton radiation verifies the conversion from MLCT to more forbidden CC state of [PhPXZDBFDP]2Cu4I4. In opposite, after offsetting time for carrier transportation, EL decays of BCPO:20% [PXZDBFDP]2Cu4I4 were still slightly shorter than its PL decays, which should be attributed to direct carrier capture and recombination by [PXZDBFDP]2Cu4I4. Furthermore, along with temperature increasing from 50 to 300 K, EL decays of BCPO:20% [PhPXZDBFDP]2Cu4I4 were slightly and gradually shortened, due to enhanced thermal motion. Differently, BCPO:20% [PXZDBFDP]2Cu4I4 based devices revealed almost unchanged decays at 50 and 100 K, but markedly shortened at 200 and 300 K, which are consistent with PL decays, and manifest the electricity-driven dual emission based on the balance between relatively forbidden 3LCT state and allowed 1LCT state of [PXZDBFDP]2Cu4I4 in exciton utilization.

Time-resolved EL emission spectra (TREES) further indicate that in contrast to BCPO:20% [PhPXZDBFDP]2Cu4I4 based analogs with 80% EL emissions dispersed in 20 µs-1 ms, 90% of EL emissions from BCPO:20% [PXZDBFDP]2Cu4I4 were concentrated within 20 µs, and the rest 10% were dispersed within 100 µs, which not only reflects more rapid exciton radiation through dual emission channels, but also alleviates exciton concentration quenching (Fig. 4b). Different to limited temperature dependence of TREES for BCPO:20% [PhPXZDBFDP]2Cu4I4, long tail in TREES at 50 K of [PXZDBFDP]2Cu4I4 attributed to forbidden transitions are suddenly disappeared at 200 K, leading to highly increased emission concentration, which further demonstrates the effectiveness of dual emission in balancing singlet and triplet radiation in the devices (Supplementary Fig. 35). In Consequence, [PXZDBFDP]2Cu4I4 endowed its devices with 100% exciton utilization efficiency, owing to the combined results of (i) the highly radiative LCT featured S1 and T1 states, (ii) reversed CC→LCT energy transfer and (iii) dual emission with suppressed quenching.

Methods
Electroluminescence analysis
The devices were layer-by-layer fabricated through firstly spin-coating BCPO: x% cluster layers, and then respectively vacuum evaporating electron-transporting/injecting layers and cathodes. A system composed of a Keithley 4200 source meter, a calibrated silicon photodiode and a PR655 colorimeter was used to measure voltage-current density-luminance characteristics and electroluminescence spectra. Transient and temperature-dependent electroluminescence spectra were recorded with FLS1000 equipped with a Tektronix AFG3022G function generator.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this manuscript, the authors introduce a phenoxazine substituent group into Cu4I4 hybrid clusters via ligand engineering and report two novel clusters, [PXZDBFDP]2Cu4I4 and [PhPXZDBFDP]2Cu4I4, for the first time. Notably, the comparison between these two clusters highlights the significance of ligand design in promoting radiative processes and suppressing non-radiative quenching. The outstanding electroluminescence performance observed in [PXZDBFDP]2Cu4I4 further demonstrates the potential of ligand engineering in enhancing the efficiency of cluster-based emitters. These findings are of considerable interest and thus deserve publication in Nature Communications. However, several issues still require clarification. A few minor comments are listed below:\n1. The statement regarding “non-radiative low-lying cluster-center (CC) components including metal-metal (MMCT) and metal-couterion charge transfer (MXCT)” (Lines 34-36) is unconvincing. Previous studies (Chem. Rev. 1999, 99, 3625-3647) have shown that low-energy emissions from triplet CC excited states can indeed be radiative.\n2. According to Kasha’s rule, the emitting electronic level of a given multiplicity is the lowest excited level of that multiplicity. Why do the [PhPXZDBFDP]2Cu4I4 films exhibit dual emission?\n3. “The HOMO and LUMO energy levels of -5.37 and -3.16 eV and -5.78 and -2.98 eV”(Lines 119-120) in the article are inconsistent with the values presented in Supplementary Table 1, which is confusing. Additionally, the description of the HOMO→HOMO-2 and HOMO→HOMO-1 in Lines 122-124 does not match the data shown in Figure 1c.\n4. The PL spectrum of the neat [PhPXZDBFDP]2Cu4I4 film at 300 K shown in Supplementary Figure 7 differs significantly from that in Figure 2a. What accounts for this discrepancy?\n5. Based on Supplementary Figure 9, the [PhPXZDBFDP]2Cu4I4-based films appear to exhibit thermally activated delayed fluorescence (TADF). Why does [PhPXZDBFDP]2Cu4I4 reveal purely phosphorescent emission in Figure 2c?\n6. There are some mistakes in the sentence: “In this sense, both the singlet and triplet LCT states of [PhPXZDBFDP]2Cu4I4 nearly equally contribute to PH and TADF under a dual-emission mode, which can simultaneously reduce exciton-accumulation induced quenching and accelerate radiation.” (Lines 208-211). In this description, “[PhPXZDBFDP]2Cu4I4” should be “[PXZDBFDP]2Cu4I4” and “contraibute” should be “contribute”.", "reviewer_2": "Xu and co-workers report a bisphosphine-ligated Cu4I4 cluster that leverages radiative intra-ligand charge transfer states to achieve a high photoluminescence quantum yield (PLQY) and a notable maximum electroluminescent external quantum efficiency (EQE). While the introduction of an electron-donating phenoxazine moiety to the bisphosphine ligand improves the photoluminescent performance of the copper cluster, similar strategies, such as the incorporation of carbazole or acridine moieties, have been extensively explored in prior studies (Sci. Adv. 2019, 5, eaav9857; J. Am. Chem. Soc. 2022, 144, 6551), some of which have already achieved PLQYs as high as 90%.\nThe current study compares the standard cluster with a modified version featuring an additional phenyl spacer between the bisphosphine and phenoxazine units. However, this comparison does not appear essential, as previous work has already established the significance of nitrogen-based electron-donating groups in enhancing luminescence. Furthermore, the reported emission wavelength range (500–600 nm) is fairly common in the literature; many of multiresonant TADF materials also exhibit EQEs exceeding 30% (Nat. Photon. 2021, 15, 203; Sci. Adv. 2021, 7, eabj2504; Angew. Chem. Int. Ed. 2022, 62, e202306768; Adv. Optical Mater. 2022, 10, 2201714).\nGiven these considerations, the novelty of this work does not appear sufficient to meet the high publication standards of Nature Communications.\nAdditional Minor Comments:\n1. The authors should avoid using undefined ligand abbreviations in the abstract.\n2. The manuscript contains several typographical errors that require correction.", "reviewer_3": "The manuscript entitled “Excited State Reversal in Copper Iodide Clusters Enables 100% Exciton Radiation” reported two new electroluminescent Cu4I4 cubic clusters stabilized with phenoxazine (PXZ) functionalized biphosphine ligands. This kind of new electroluminescent organic-inorganic hybrid materials emerged rapidly in recent years. As the authors emphasized, the excited states of cluster molecules were multi-component, including non-radiative CC states and ligand-incorporated charge transfer and locally excited states. The direct and energy transfer-induced populations of CC states were believed as the key issue inducing energy loss and efficiency reduction. Although there were many works reported the excited state engineering of cluster emitters, reversing the energy levels of CC states and ligand centered excited states would be ideal to avert CC-induced quenching. In this work, through introducing a strong PXZ donor in the D-A ligand, the so-called excited state reversal of [PXZDBFDP]2Cu4I4 cube was realized, leading to efficient dual emission with 52% TADF and 48% phosphorescence (PH). The authors also prepared another cluster emitter [PhPXZDBFDP]2Cu4I4 with a D-π-A ligand, which features the normal low-lying MC states. As a result, [PXZDBFDP]2Cu4I4 realized the state-of-the-art performance, e.g. PLQY of ~90%, and the maximum EQE as high as 35.5%, which is the record-high value for EL homo-copper clusters.. Although the maximum value of EL efficiencies for [PXZDBFDP]2Cu4I4 as the second high value reported so far was about 0.1% lower than the record, roll-offs of [PXZDBFDP]2Cu4I4 based device were markedly reduced. As a result, its efficiencies at 100 and 1000 nits are record high. This work not only breaks through the performance bottleneck of EL clusters, but also provides a new and very important insight into excited state optimization for multi-component systems. Therefore, this paper deserved to be published on Nature Communications after minor revision.\nSome detailed comments:\n1. To make the materials can be prepared by other groups, the comprehensive characterization of chemical structures should be modified. Some important evidences, such as NMR data and spectra, should be added in supporting information.\n2. Considering the importance of excited state reversal, besides Gaussian simulation results, can the authors provide the experimental evidences to demonstrate such reversed excited states, e.g. the assignment of absorption peaks for CC and LC.\n3. In neat film, [PhPXZDBFDP]2Cu4I4 had two peaks. Although according to the absorption and excitation spectra, the lowest excited states of [PhPXZDBFDP]2Cu4I4 would be CC state. However, the dual-peak emissions of this cluster should be used to further demonstrate the excited-state evolution. So, the transient investigation of CC and LC states should provide.\n4. I noticed that PL and EL spectra of [PhPXZDBFDP]2Cu4I4 were completely different, therefore, a more detailed explanation on the stronger long-wavelength band in EL spectra should be added. As the other side of the coin, why were PL and EL spectra for [PXZDBFDP]2Cu4I4 the same? In addition, some references on TADF and PH of Cu-clusters should be cited into the paper, for example, 10.31635/ccschem.022.202101741, Nature Communications, 2024, 15, 9401 (PH properties of Cu-NCs), CCS Chem., 2024, 6, 2537 (TADF properties of Cu-NCs), etc.", "reviewer_4": "This manuscript reports the study of two molecular copper iodide clusters as emitters for light-emitting diodes applications. By employing a ligand engineering strategy based on the increase of the donor-acceptor effect, change of the relative energy of the excited states was achieved that favors exciton radiation. A high value of EL external quantum efficiency is thus reported for the studied compounds, that is the record for cluster-based LED. Although this approach has already been investigated by the authors with chemically close compounds (Angew. Chem. 2023 e202305018, ref.51), a record is established promoting the interest of the domain. The comparison of the two clusters having slightly different ligands, is very informative, the work is well conducted and the results are convincing. For these reasons, this work can be recommended for publication in Nature Communications, providing the following points are taken into account.\n- The elemental analyses of the two clusters are missing.\n- The 31P NMR data of [PhPXZDBFDP]2Cu4I4 are missing.\n- Line 16 page 4, HOMO+1 and HOMO+2 should be corrected by HOMO-1 and HOMO-2.\n- The SCXRD analysis should be clearly mentioned in the text and the crystallographic data provided in the SI.\n- The emission spectra of [PhPXZDBFDP] (100%) in Figures 2a and S7 are not really consistent. The two emission bands are clearly less resolved in Figure S7. The moderate temperature change of the CC band is different from the classical thermochromic effect for these clusters. The authors should discuss this point.\n- Only one cycle of cyclic voltammetry is presented in Figure S3 for each cluster. The authors should mention if there is degradation after multiple cycles."}, "author_response": "Responses to Reviewers’ Comments\nReviewer #1:\nGeneral comment: In this manuscript, the authors introduce a phenoxazine substituent group into Cu4I4 hybrid clusters via ligand engineering and report two novel clusters, [PXZDBFDP] Cu I and\n2 4 4\n[PhPXZDBFDP] Cu I , for the first time. Notably, the comparison between these two clusters highlights\n2 4 4\nthe significance of ligand design in promoting radiative processes and suppressing non-radiative\nquenching. The outstanding electroluminescence performance observed in [PXZDBFDP] Cu I further\n2 4 4\ndemonstrates the potential of ligand engineering in enhancing the efficiency of cluster-based emitters.\nThese findings are of considerable interest and thus deserve publication in Nature Communications.\nHowever, several issues still require clarification. A few minor comments are listed below.\nResponse: Reviewer’s kind approval and accurate summary of our work is highly appreciated. Thanks a\nlot!\n1. The statement regarding “non-radiative low-lying cluster-center (CC) components including metal-\nmetal (MMCT) and metal-couterion charge transfer (MXCT)” (Lines 34-36) is unconvincing. Previous\nstudies (Chem. Rev. 1999, 99, 3625-3647) have shown that low-energy emissions from triplet CC excited\nstates can indeed be radiative.\nResponse: Thanks a lot for this constructive comment! As the reviewer pointed out, “non-radiative” is not\naccurate for describing the transition feature of CC states, since there were previous reports about\nemissions from CC states. Actually, what we want to emphasize is that regarding to emission, the CC\nstates of copper iodide clusters were commonly less efficient than their ligand centered (LC) excited\nstates. To demonstrate this point, we made a comprehensive literature searching and listed the\nrepresentative reports of clusters featuring CC and LC predominant radiations for electroluminescence\n(Table R1). It shows that despite few examples with high PLQY, most of CC-predominant clusters\nrevealed PLQY values less than 50%, and the maximum EQE values of their devices hardly reached 10%.\nIn contrast, recently reported LC-predominant clusters can commonly achieve the PLQY and EQE more\nthan 80% and 20%, respectively, which verified the superiority of LC states for radiation.\nThe related sentence was revised to improve accuracy. The “Chemical Review” paper was cited\nin the reference section. Thanks a lot!\nS1\nTable R1. Comparison of excited state types and efficiency for selected representative CLEDs.\nη\nRadiative Chemical PLQY\nCluster η (cd η (lm η Ref.\nState Structure CE PE EQE (%)\nA-1) W-1) (%)\nJ. Mater. Chem.,\n[Cu(μ-X)dpmb] 32.9 19.9 10.1 32\n2 2012, 22, 20786\nACS Materials\nCu(I)-CTC 7.21 - 4 99\nLett. 2022, 4, 1921\nCluster\nCentered\nSci. Adv. 2019, 5,\nStates (CC) [DBFDP] Cu I 1.8 0.5 0.7 5\n2 4 4 eaav9857\nNat. Commun.\nR-py-I - - - 45.3\n2023, 14, 4121\nAdv. Mater.\n[Cu (P, N, P) ] 73 - 23 92\n2 2 2015,27,2538\n[DtBCzDBFDP] Sci. Adv. 2019, 5,\n20.2 10.6 7.9 65\nCu I eaav9857\n2 4 4\nLigand\nCentered\nStates (LC) [Cu (PCP) ][BA J. Am. Chem. Soc.\n4 3 42 - 11.2 93\nrF ] 2020, 142, 373\nR-ql-I 59.2 23.3 20.8 93.0\n2023, 14, 4121\nCu I [P-(m- Nat. Photonics.\n2 2 43.5 - 19.1 82.8\nTol) ] 2024, 18, 200\n3 2\nS2\nJ. Am. Chem. Soc.\nCu Au (R-BTT) 134.1 82.6 36.5 94\n2 2 4 2024, 146, 4144\n[PXZDBFDP] C\n2\nu I 95.9 75.3 35.5 89.7 This word\n4 4\nRevision:\nDiscussion on radiative feature of CC state was revised:\n“But, they simultaneously exhibit complicated excited states composed of not only efficiently\nradiative high-lying ligand-centered (LC), e.g. metal/counterion-ligand charge transfer (Mn/XLCT),\nintraligand (LCT) and interligand charge transfer (ILCT) and locally excited (LE) states, but also low-\nlying cluster-center (CC) components including metal-metal (MMCT) and metal-counterion charge\ntransfer (MXCT) inferior in radiation.22”\n“22. Ford PC, Cariati E, Bourassa J. Photoluminescence Properties of Multinuclear Copper(I)\nCompounds. Chem Rev99, 3625-3648 (1999).”\n2. According to Kasha’s rule, the emitting electronic level of a given multiplicity is the lowest\nexcited level of that multiplicity. Why do the [PhPXZDBFDP] Cu I films exhibit dual emission?\n2 4 4\nResponse: Thanks a lot for this constructive comment! We should apologize for our unclear and\ninsufficient explanation. Actually, such “dual emission” is a common property for copper iodide clusters\n(J. Am. Chem. Soc. 1991, 113, 2954-2965), which is originated from their multicomponent excited states\nconsisting of ligand-centered (LC) and cluster-centered (CC) components, respectively corresponding to\nhigh-energy (HE) and low-energy (LE) emission bands (please see Figure R1). LC components are\ncomposed of metal-ligand charge transfer (MLCT) and intra- and inter-ligand charge transfer (LCT)\nstates, primarily involving in Cu-I bond lengthening and Cu-P bond shortening; while, CC components\nfeature d-d transitions, primarily involving contraction and deformation of the Cu I core (Acc. Chem. Res.\n4 4\n1993, 26, 220-226). This distinct geometrical reorganization effectively separates the potential energy\nsurfaces of LC and CC states in configurational space. Therefore, internal transitions from the HE bands\nS3\nto the LE bands are spatially forbidden to induce the extremely slow transition rates between them,\nresulting in the independent observation of HE and LE bands, namely dual emission (Chem. Rev. 1999,\n99, 3625-3647).\n[FIGURE REDACTED]\nFigure R1. (a-c) The structures and PL spectra of representative Cu I cubes featuring two emission\n4 4\nbands; (d) Structure and temperature dependent PL spectra of [PhPXZDBFDP] Cu I in our work.\n2 4 4\nTDDFT simulation shows that the excited states of [PhPXZDBFDP] Cu I are also localized on\n2 4 4\nits coordination skeleton, which are composed of LC and CC components, corresponding to HE and LE\nbands. Since its excited-state characteristics are highly similar to the previous reports of Cu I cubes,\n4 4\n[PhPXZDBFDP] Cu I exhibits typical temperature-sensitive dual emission (Figure R1c). The\n2 4 4\ndiscussions and references were added in the relative section. Thanks a lot!\nRevision:\nExplanation of two emission bands from [PhPXZDBFDP] Cu I was revised:\n2 4 4\n“In contrast, neat [PhPXZDBFDP] Cu I film reveals two emission peaks at 522 and 626 nm\n2 4 4\noriginated from its high-energy MLCT and low-energy CC states with different geometrical\nreorganization,49, 50 which is similar to donor-free [DBFDP] Cu I in accord to their identical CC-featured\n2 4 4\nS and T states.22, 39”\n1 1\nS4\n49. Kyle KR, Ryu CK, Ford PC, DiBenedetto JA. Photophysical studies in solution of the\ntetranuclear copper(I) clusters Cu4I4L4 (L = pyridine or substituted pyridine). J Am Chem Soc113, 2954-\n2965 (1991).\n50. Ford PC, Vogler A. Photochemical and photophysical properties of tetranuclear and hexanuclear\nclusters of metals with d10 and s2 electronic configurations. Acc Chem Res26, 220-226 (1993).\n3. “The HOMO and LUMO energy levels of -5.37 and -3.16 eV and -5.78 and -2.98 eV”(Lines 119-\n120) in the article are inconsistent with the values presented in Supplementary Table 1, which is\nconfusing. Additionally, the description of the HOMO→HOMO-2 and HOMO→HOMO-1 in Lines 122-\n124 does not match the data shown in Figure 1c.\nResponse: Thanks a lot for this constructive comment! We should apologize for our carelessness inducing\nthese typos. The data of experimentally measured HOMO and LUMO energy levels listed in\nSupplementary Table 1 were correct. The energy gap between the HOMO and the HOMO-2 of\n[PXZDBFDP] Cu I is 0.163 eV, which is double of the HOMO-HOMO-1 gap for\n2 4 4\n[PhPXZDBFDP] Cu I . The manuscript was rechecked carefully to get rid of these typos and grammar\n2 4 4\nerrors. Thanks a lot!\nRevision:\nThe typos was corrected:\n“On the contrary to the situation of [PhPXZDBFDP] Cu I , the HOMO-1 and HOMO-2 of\n2 4 4\n[PXZDBFDP] Cu I are respectively contributed by PXZ and Cu I core, reflecting the stronger D-A\n2 4 4 4 4\ninteractions. Consequently, [PXZDBFDP] Cu I exhibits the shallower HOMO and deeper lowest\n2 4 4\nunoccupied molecular orbital (LUMO), compared to [PhPXZDBFDP] Cu I , which are consistent with\n2 4 4\nthe HOMO and LUMO energy levels of -5.46 and -3.01 eV and -5.50 and -2.84 eV experimentally\nestimated with cyclic voltammetry (CV) analysis (Supplementary Figs 22 and 23 and Supplementary\nTable 5). Furthermore, the energy gap between the highest occupied molecular orbitals on PXZ and Cu I\n4 4\ncore is 0.163 eV for [PXZDBFDP] Cu I (HOMO→HOMO-2), which is more than doubled in\n2 4 4\ncomparison to that of [PhPXZDBFDP] Cu I (HOMO→HOMO-1).”\n2 4 4\nS5\n4. The PL spectrum of the neat [PhPXZDBFDP] Cu I film at 300 K shown in Supplementary\n2 4 4\nFigure 7 differs significantly from that in Figure 2a. What accounts for this discrepancy?\nResponse: Thanks a lot for this constructive comment! We should apologize for our carelessness in\nconsistence of sample preparation and measurement. The difference in PL spectra for neat\n[PhPXZDBFDP] Cu I film in Figure 2a and Supplementary Figure 7b was induced by the different film\n2 4 4\npreparation recipes. The thickness of the film used for temperature dependence of PL spectra was only a\nhalf of that used for Figure 2a, weakening 3CC emission. Therefore, we re-prepared the thinker film and\nre-measured the spectra, which show the remarkable changes from HE bands to LE bands along with\ntemperature decreasing, which is in accord to previous reports of thermochromic feature for Cu I cubes\n4 4\n(Figure R1).\nSupplementary Figure 27b was redrawn, and the related descriptions were revised. Thanks a lot!\nRevision:\nSupplementary Figure 27b and related description were revised:\nSupplementary Fig. 27. PL spectra of neat films based on (a) [PXZDBFDP] Cu I and (b)\n2 4 4\n[PhPXZBFDP] Cu I at different temperatures.\n2 4 4\n“PL spectra of neat [PXZDBFDP] Cu I are nearly independent on temperature. But, neat\n2 4 4\n[PhPXZDBFDP] Cu I film shows the remarkable changes from HE bands to LE bands along with\n2 4 4\ntemperature decreasing.”\nS6\n5. Based on Supplementary Figure 9, the [PhPXZDBFDP] Cu I -based films appear to exhibit\n2 4 4\nthermally activated delayed fluorescence (TADF). Why does [PhPXZDBFDP] Cu I reveal purely\n2 4 4\nphosphorescent emission in Figure 2c?\nResponse: Thanks a lot for this constructive comment! As reviewer pointed out, in doped films, long-\nlifetime components from [PhPXZDBFDP] Cu I seems increasing along with temperature. However, it\n2 4 4\ncan be noted that its neat film shows the opposite tendency (Supplementary Figure 28a), which actually\ndemonstrates the triplet quenching at high temperature, corresponding to PH feature. However, for\nBCPO:20% [PhPXZDBFDP] Cu I film, the BCPO host matrix effectively suppresses the collisional\n2 4 4\nquenching, therefore making triplet states from coordination skeleton of [PhPXZDBFDP] Cu I can be\n2 4 4\nradiative (Supplementary Figure 28b). It can also be noticed that despite slightly elongating, the time\nscale of decays from the doped film is almost unchanged, indicating the small regulation on radiative\nratios between different kinds of triplet state components. Therefore, it is convincing that along with\ntemperature increasing, the radiative states of BCPO:20% [PhPXZDBFDP] Cu I film partially change\n2 4 4\nfrom 3MLCT state with higher radiative rate constant to 3CC state with lower radiative rate, rendering the\nlifetime slightly increasing. It is because 3MLCT transition is partially forbidden, but 3CC transition is\nforbidden.\nThe related descriptions and discussions were revised for improving clarity. Thanks a lot!\nRevision:\nDescription and discussion on temperature dependence of time decays for BCPO:20%\n[PhPXZDBFDP] Cu I film were revised:\n2 4 4\n“Furthermore, although collisional quenching of neat [PhPXZDBFDP] Cu I film is worsened by\n2 4 4\nincreasing temperature and therefore induces gradually decrease of lifetime, with suppressed inter-cluster\ninteractions, lifetime of BCPO:20% [PhPXZDBFDP] Cu I becomes directly proportional to temperature,\n2 4 4\nin accord to the conversion from partially forbidden 3MLCT to forbidden 3CC state with smaller radiative\nrate constant (Supplementary Fig. 28).”\n“However, it can be noted that lifetimes of neat [PhPXZDBFDP] Cu I film are in reverse proportion\n2 4 4\nto temperature, which actually demonstrates the triplet quenching at high temperature, corresponding to\nPH characteristics (Supplementary Figure 28a). However, for BCPO:20% [PhPXZDBFDP] Cu I film,\n2 4 4\nBCPO host matrix effectively suppresses the collisional quenching, therefore making all triplet state\ncomponents from coordination skeleton of [PhPXZDBFDP] Cu I can be radiative (Supplementary\n2 4 4\nFigure 29b). Furthermore, despite slightly elongating, the time scale of decays for the doped film is\nS7\nalmost unchanged, indicating the small regulation on radiative ratios between different kinds of triplet\nstate components, namely the shift between partially forbidden 3MLCT and forbidden 3CC components.”\n6. There are some mistakes in the sentence: “In this sense, both the singlet and triplet LCT states of\n[PhPXZDBFDP] Cu I nearly equally contribute to PH and TADF under a dual-emission mode, which\n2 4 4\ncan simultaneously reduce exciton-accumulation induced quenching and accelerate radiation.” (Lines\n208-211). In this description, “[PhPXZDBFDP] Cu I ” should be “[PXZDBFDP] Cu I ” and “contraibute”\n2 4 4 2 4 4\nshould be “contribute”.\nResponse: Thanks a lot for this constructive comment! We should apologize for our carelessness during\nmanuscript preparation, inducing these typos. We rechecked the manuscript and tried our best to get rid of\nthe typos and grammar errors. Thanks a lot!\nRevision:\nTypos and grammar errors were corrected:\n“In this sense, both the singlet and triplet LCT states of [PXZDBFDP] Cu I nearly equally\n2 4 4\ncontraibute to PH and TADF under a dual-emission mode, which can simultaneously reduce exciton-\naccumulation induced quenching and accelerate radiation.”\nS8\nReviewer #2:\nGeneral comment: Xu and co-workers report a bisphosphine-ligated Cu I cluster that leverages radiative\n4 4\nintra-ligand charge transfer states to achieve a high photoluminescence quantum yield (PLQY) and a\nnotable maximum electroluminescent external quantum efficiency (EQE). While the introduction of an\nelectron-donating phenoxazine moiety to the bisphosphine ligand improves the photoluminescent\nperformance of the copper cluster, similar strategies, such as the incorporation of carbazole or acridine\nmoieties, have been extensively explored in prior studies (Sci. Adv. 2019, 5, eaav9857; J. Am. Chem. Soc.\n2022, 144, 6551), some of which have already achieved PLQYs as high as 90%. The current study\ncompares the standard cluster with a modified version featuring an additional phenyl spacer between the\nbisphosphine and phenoxazine units. However, this comparison does not appear essential, as previous\nwork has already established the significance of nitrogen-based electron-donating groups in enhancing\nluminescence. Furthermore, the reported emission wavelength range (500–600 nm) is fairly common in\nthe literature; many of multiresonant TADF materials also exhibit EQEs exceeding 30% (Nat. Photon.\n2021, 15, 203; Sci. Adv. 2021, 7, eabj2504; Angew. Chem. Int. Ed. 2022, 62, e202306768; Adv. Optical\nMater. 2022, 10, 2201714). Given these considerations, the novelty of this work does not appear\nsufficient to meet the high publication standards of Nature Communications.\nResponse: Thanks a lot for reviewer’s comments and kind approval of the performances reported in this\nwork. We should apologize for our insufficient description and explanation on the novelty of this work,\nin comparison with our previous reports and other kinds of electroluminescent systems. We would like to\nresponse to reviewer’s concerns from two aspects as following:\n(i) [PXZDBFDP] Cu I in this work demonstrates that ligand-localized states can be the lowest\n2 4 4\nexcited states, which is opposite to our previous reports about core-involved states were the lowest.\nIt is known that the excited state compositions of cluster emitters are complicated, including cluster\ncore involved components, e.g. metal/counterion-ligand charge transfer (Mn/XLCT) and metal-metal\n(MMCT) and metal-counterion charge transfer (MXCT), and ligand-localized components, e.g.\nintraligand (LCT) and interligand charge transfer (ILCT) and locally excited (LE) states. The former are\ninferior to the latter with respect to luminescent efficiencies. However, nearly all clusters reported so far\nshow the lowest excited states involving cluster cores, which not only direct reduce radiative efficiencies,\nbut also induce quenching of ligand-localized excited states by energy transfer, therefore limiting their\nluminescent performances. In this sense, if the ligand-centered excited states can be the lowest, high-\nperformance luminescent clusters should be achieved.\nIn Sci. Adv. 2019, 5, eaav9857, we reported carbazole modified Cu I clusters, in which\n4 4\n[PXZDBFDP] Cu I reveals the T state composed of 3LCT (62%), 3LLE (21%) and 3(M+X)LCT (17%)\n2 4 4 1\n(Figure R2a); while, in J. Am. Chem. Soc. 2022, 144, 6551, acridine-modified [DPACDBFDP] Cu I\n2 4 4\nS9\nindicates the T state containing 80% of iodine-ligand CT and 20% of metal-ligand CT (Figure R2b).\nlocalized states. On the contrary, in this work, [PXZDBFDP] Cu I successfully achieves thoroughly\n2 4 4\nligand-confined FMOs and the ligand-localized first singlet (S ) and triplet (T ) excited states with\n1 1\noccupied and unoccupied orbitals respectively localized on PXZ and dibenzofuran (DBF) (Figure R2c);\nwhile, its Cu I core reversely contributes to the high-lying S and T states. In this case of abnormal\n4 4 3 3\nexcited state reversal, [PXZDBFDP] Cu I can not only realize ~90% PLQY by its highly radiative S and\n2 4 4 1\nT states, but also achieve the state-of-the-art EQE over 35%, since the non-radiative CC states are\n1\nconverted to LCT state rather than capturing and quenching excitons. Actually, up to present, 35.5% of\nEQE is the record high value for copper clusters based devices.\n[FIGURE REDACTED]\nFigure R2. Comparison on excited state characteristics of Cu I clusters and 3CC elimination approaches\n4 4\nwe reported previously.\nS10\nIt can be noted that although the PLQY values of the clusters reported in Sci. Adv. 2019, 5, eaav9857\nand J. Am. Chem. Soc. 2022, 144, 6551 are quite high, their 3CC states as the lowest states directly\ncaptured and quenched excitons in their devices, rendering relatively lower EQE values of 8% and 19%,\nin comparison to 35.5% reported in this work. Therefore, in addition to energy transfer, the direct capture\nof the lowest excited state by charge can also lead to quenching. Actually, in our previous works, through\nhost engineering, the triplet excitons were either confined to ligand-centered triplet states (Figure R2d) or\nupconverted to singlet by TADF host matrixes (Figure R2e), therefore averting the direct triplet capture\nand quenching by 3CC states, which can indeed improve EQE. In this work, the excited state reversal in\n[PXZDBFDP] Cu I undoubtedly solves this problem from the origin, owing to its ligand-confined S and\n2 4 4 1\nT states energetically lower than its cluster-centered states. In this sense, this work undoubtedly provides\n1\na new insight into manipulating excited states of clusters for high-performance optoelectronic applications.\n(ii) [PXZDBFDP] Cu I endows its solution-processed devices with the state-of-the-art\n2 4 4\nefficiencies not inferior to the best results of all the other kinds of light-emitting devices.\nFirst of all, please allow me to emphasis the state-of-the-art efficiencies of [PXZDBFDP] Cu I -\n2 4 4\nbased devices: 95.9 cd A-1 for current efficiency, 75.3 lm W-1 for power efficiency and 35.5% for EQE,\nrespectively, which dramatically improve the efficiency record of CLEDs based on copper clusters by\nabout one fifth. To make rational comparison with other kinds of light-emitting devices, we performed a\nsystematic literature searching of recently reported high-efficiency planar light-emitting devices based on\norganic TADF/MR emitters, perovskites, quantum dots and clusters, which are summarized in Table R1.\nAs reviewer mentioned, TADF and MR emitters were developed rapidly in recent ten years, some of\nthem can realize the maximum EQE beyond 35% and even reaching 40%. However, nearly all of these\nresults were based on devices fabricated by vacuum evaporation, and some of them were achieved by out-\ncoupling assistance. When adopting solution processing technologies, e.g. spin coating, the maximum\nEQE values of TADF/MR devices can be hardly beyond 30%. Meanwhile, for perovskites and quantum\ndots based devices reported in the top-rank journals, only very few of them can realize the maximum EQE\nmore than 35%. For cluster light-emitting devices, their maximum EQE values were mostly less than 30%.\nUp to now, in addition to one Cu Au alloy cluster with the maximum EQE of 36.5% (J. Am. Chem. Soc.\n2 2\n2024, 146, 4144), [PXZDBFDP] Cu I is one of the only two clusters reported so far achieving the\n2 4 4\nmaximum EQE values beyond 35%. It should be noted that in J. Am. Chem. Soc. 2024, 146, 4144,\ndespite its slightly higher maximum EQE, the EQE of Cu Au cluster based device sharply decreased to\n2 2\n~10% at 500 nits. In contrast, the EQE values of [PXZDBFDP] Cu I based devices still remained 25.5%\n2 4 4\nat 500 nits. So, it is convincing that among all kinds of electroluminescent systems, [PXZDBFDP] Cu I\n2 4 4\nis undoubtedly one of the best emitters reported so far.\nWe wish reviewer would like to agree with our opinion. Thanks a lot!\nS11\nThe related discussions were revised to emphasize the novelty of this work and the importance of the\nresults. Thanks a lot!\nTable R1. Comparison on EL performances of representative emitting systems, including TADF\nmolecules, clusters, perovskites and quantum dots.\nη[c]\nϕ λ [d]\nPA[a] Device structure Emitter PL[b] EL Ref.\n(%) η CE η PE η EQE (nm)\n(cd A-1) (lm W-1) (%)\nITO/a-NPD (35\nnm) /6 wt%\n4CzIPN:CBP (15 Nature. 2012,\n94 60 50 19.3 507\nnm) /TPBi (65 492, 234\nnm) /LiF (0.8 nm)\n/Al (70 nm)\n4CzIPN\nITO(50 nm)/HAT-\nCN(10 nm)/Tris-\nPcz(10 nm)/mCBP\n(5 nm)/0.5 wt% ν-\nDABNA:20 wt% Nat. Photon.\n86 72 23 41 470\nHDT-1:mCBP (30 2021, 15, 203\nnm)/SF3-TRZ (10\nnm)/SF3-TRZ:Liq\nHDT-1\n(25 nm)/Liq (2\nnm)/Liq(2nm)/Al\nITO/HATCN (5\nVE nm)/TAPC (50\nnm)/TCTA (5\nnm)/mCP (5\nnm)/25 wt% TCP- Sci. Adv. 2021,\n99 74.3 68.6 38.6 480\nBP-SFAC:DPEPO 7, eabj2504\n(20 nm)/DPEPO\nTCP-BP-SFAC\n(5 nm)/TmPyPB\n(30 nm)/LiF (1\nnm)/Al\nITO (50\nnm)/HATCN (7\nnm)/TAPC (50\nnm)/DCDPA (10 Angew. Chem.\nnm)/DBFPO: 25 Int. Ed. 2023,\n83.4 29.2 - 33.7 469\nwt% NO-DBMR 62,\n(25 nm)/DBFPO e202306768\nNO-DBMR\n(5 nm)/TPBi (20\nnm)/LiF (1.5\nnm)/Al (100 nm)\nS12\nITO/PEDOT:PSS\n(40\nnm)/DMICTRZ: 5\nAngew. Chem.\nwt% BN-36Cz–\nInt. Ed. 2023,\nSC BN (40 nm)/PO- 65 61.8 55.4 27.1 495\n62,\nT2T (20\ne202301988\nnm)/ANT-BIZ (30 BN-36Cz–BN\nnm)/Liq (1 nm)/Al\n(100 nm)\nITO/PVK:\nAdv. Mater.\nCu (C≡CPh) L\n4 4 2 0.42 - - 0.1 512 1999, 11, No.\n(10 wt%, 100\n10\nnm)/TAZ/Al\nCu (C≡CPh) L\n4 4 2\nITO (22 nm)/CFx\n(1 nm)/TAPC (75 tBu\ntBu\nnm)/CBP: 25%\nwt% TAPC (10 iBu2PH PHiBu2\nnm)/CBP: 25 wt% N J. Am. Chem.\nCu Cu\nTAPC: 0.2% N 57 47.5 - 16.1 512 Soc. 2010,\n[Cu(PNP-tBu)] iBu2PH PHiBu2 132, 9499\n2\n(35 nm)/CBP (10 tBu\nnm)/BAlq-13 (40\ntBu\nnm)/LiF (0.5 [Cu(PNP-tBu)] 2\nSC nm)/Al(120 nm)\nITO/PEDOT:PSS\n(30nm)/PLEXCR\nE UT-314 (45\nnm)/PYD2: [Cu Adv. Mater.\n2 92 73 - 23 530\n(P,N,P) ] (30 wt%, 2015, 27, 2538\n2\n27nm)/3TPYMB\n(50 nm)/LiF (2 [Cu (P,N,P) ]\n2 2\nnm)/Al\nITO/PEDOT：\nPSS (40\nnm)/TAPC (40\nnm)/ J. Am. Chem.\nTAPC:[2][BArF₄] 93 42 - 11.2 518 Soc. 2020,\n(5 wt%) (40 142, 373\nnm)/B3PYMPMP\nM (40 nm)/LiF (1\nnm)/Al\n[Cu (PCP) ][BArF ]\n4 3 4\nS13\nITO/PEDOT:PSS\n/mCP:S-ql-I (2 Nat. Commun.\n93.0 59.2 23.3 20.8 586\nwt%) / DPEPO 2023, 14, 4121\n/TmPyPB /Liq /Al\nR/S-ql-I\nITO/PEDOT :\nPSS/Poly-TPD\nAngew. Chem.\n/40% Ag Cu: 2,6-\n6 91.8 26.4 22.9 26.7 653 Int. Ed. 2024,\nDCzPPy : OXD-7\ne202417934\n(1:1)/BmPyPb\n/LiF/Al\nR-Ag Cu\nPEDOT:PSS/TCT\nJ. Am. Chem.\nA: 20 wt%\n94 134.1 82.6 36.5 540 Soc. 2024,\nCu Au (R-\n2 2 146, 4144\nBTT) /TPBi (35\n4\nnm)/LiF (1 nm)/Al Cu 2 Au 2 (R-BTT) 4\nITO/PEDOT:PSS\n(39 nm)/poly-TPD\n(26 nm)/PVK (28 Nat. Photon.\n82.8 43.5 - 19.1 560\nnm)/CuI-Pyrphos 2024, 18, 200\n(39 nm)/TmPyPB\n(55 nm)/LiF/Al\nCu I [P-(m-Tol) ]\n2 2 3 2\nITO/PEDOT:PSS\n(40\nnm)/BCPO:[PhPX\nZDBFDP] Cu I\n2 4 4 89.7 95.9 75.3 35.5 507 This word\n(20%wt., 40\nnm)/TmPyPB (50\nnm)/LiF (1 nm)/Al\n(100 nm)\n[PXZDBFDP] Cu I\n2 4 4\nITO/PEDOT:PSS\n(20\nnm)/MAPbBr /PV\n3 65- Adv. Mater.\nSC K:PBD (64: 36 CH NH PbBr - 1.0 0.48 530\n3 3 3 85 2015, 28, 305\nwt%, 30 nm)/BCP\n(50 nm)/ LiF (1\nnm)/Al(150 nm)\nS14\nITO/ZnO-PEIE\n(30 nm)/5AVA-\nNature. 2018,\nFAI- HC(NH ) PbI 70 - - 20.7 803\n2 2 3 562, 249\nPbI /TFB/MoOx/\nITO/ZnO/PEIE/F\nNat. Commun.\nA Cs PbI /TFB/ (FA Cs )PbI 70 - - 19.6 780\n0.9 0.1 3 0.9 0.1 3 2019, 10, 2818\nMoO /Ag\nPEIE/FAPbI :\n0DEA(50 nm)/TF FAPbI - - - 21.2 804\n3 2020, 3, 156\n(40 nm)/MoOₓ (7\nnm)/Au (80 nm)\nITO/ZnO-PEIE\n(30 nm)/FAPbI\n(60 nm)/TFB (20 FAPbI 96 - - 32.0 805\n3 630, 631\nnm)/MoO (5\nx\nnm)/Au(80 nm)\nITO/Ac2PACz-\nNiO /CuI(Hda)(90 Nature. 2025,\nx CuI(Hda) 99.6 11.2 8.4 12.5 449\nnm)/PMMA/Ca(ac 643, 1246\nac) /LiF/Al\nCdSe - - - 0.01 -\ng/Ag 370, 354\nITO/PEDOT:PSS\n(35 nm)/poly-TPD\n(30 nm)/PVK (5\nNature. 2014,\nnm)/CdSe- CdSe-CdZnS - - 20.5 640\n515, 96\nCdS/PMMA (6\nnm)/ZnO (150\nnm)/Ag(100 nm)\nITO (32\nnm)/PEDOT: PSS:\nPFI (210 nm)/\nPEA Cs MA Pb PEA Cs MA Pb Nature. 2021,\n2 1.6 0.4 2 1.6 0.4 3 90 88 - 25.6 520\nBr (60 Br 599,594\n3 10 10\nnm)/3TPYMB (40\nnm)/LiF (1 nm)/Al\n(150 nm)\nITO/PEDOT:PSS/\nNature. 2024,\nPF8Cz/InP-ZnSe- InP-ZnSe-ZnS 94.5 112.5 - 26.7 543\n635,854\nZnS/ZnMgO/Al\nS15\nITO/PEDOT:PSS/\nTFB/CdZnSe-\nCdZnSe-ZnSe-ZnS 80 - 35.6 640 Photon.2024,\nZnSe-\n18, 186\nZnS/ZnMgO/Al\nITO/PEDOT:PSS/\nTFB:CBPV/InAs- Nat. Commun.\nInAs-InP-ZnSe-ZnS 100 - - 20.5 905\nInP-ZnSe- 2025, 16, 2450\nZnS/ZnMgO/Ag\n[a] PA, VE and SC refer to processing approaching, vacuum evaporation and spin coating; [b]\nphotoluminescence quantum yield (PLQY); [c] the maximum efficiencies; [d] EL peak wavelengths.\nRevision:\nThe novelty and importance of this work were explained:\n“Actually, in most cases of clusters, one of the intrinsic issue is CC states energetically lower than\nLC states, therefore, it is difficult to completely prevent LC→CC energy transfer; meanwhile, the\nincorporation of Cu+ and I- in frontier molecular orbitals (FMO) inevitably induces the direct charge and\nexciton capture by Cu I cores during EL processes.”\n4 4\n“Actually, [PXZDBFDP] Cu I is one of the only two clusters reported so far can realize the\n2 4 4\nmaximum η beyond 35% (Fig. 3e and Supplementary Table 6). It is noteworthy that compared to the\nEQE\nother one with sharply decreased η of ~10% at 500 nits, [PXZDBFDP] Cu I is more superior in\nEQE 2 4 4\nefficiency stability at high luminance, evidenced by its η remaining 32.4% and 25.0% at 100 and 500\nEQE\nnits, corresponding to markedly reduced EQE roll-offs of 8.7% and 29.6%.”\n1. The authors should avoid using undefined ligand abbreviations in the abstract.\nResponse: Thanks a lot for this comment. The full names of the ligands were added in the abstract.\nThanks a lot!\nRevision:\nFull names of the ligands were added:\n“PXZDBFDP = 10-(4,6-bis(diphenylphosphino)dibenzo[b,d]furan-2-yl)-10H-phenoxazine”\n“PhPXZDBFDP = 10-(4,6-bis(diphenylphosphino)dibenzo[b,d]furan-2-yl)-10H-phenylphenoxazine”\nS16\n2. The manuscript contains several typographical errors that require correction.\nResponse: Thanks a lot for this comment. We should apologize for our carelessness during manuscript\npreparation, inducing these typos. We rechecked the manuscript and tried our best to get rid of the typos\nand grammar errors. Thanks a lot!\nRevision:\nTypos and grammar errors were corrected:\n“In this sense, both the singlet and triplet LCT states of [PXZDBFDP] Cu I nearly equally\n2 4 4\ncontraibute to PH and TADF under a dual-emission mode, which can simultaneously reduce exciton-\naccumulation induced quenching and accelerate radiation.”\n“On the contrary to the situation of [PhPXZDBFDP] Cu I , the HOMO-1 and HOMO-2 of\n2 4 4\n[PXZDBFDP] Cu I are respectively contributed by PXZ and Cu I core, reflecting the stronger D-A\n2 4 4 4 4\ninteractions. Consequently, [PXZDBFDP] Cu I exhibits the shallower HOMO and deeper lowest\n2 4 4\nunoccupied molecular orbital (LUMO), compared to [PhPXZDBFDP] Cu I , which are consistent with\n2 4 4\nthe HOMO and LUMO energy levels of -5.46 and -3.01 eV and -5.50 and -2.84 eV experimentally\nestimated with cyclic voltammetry (CV) analysis (Supplementary Fig. 22 and 23 and Supplementary\nTable 5). Furthermore, the energy gap between the highest occupied molecular orbitals on PXZ and Cu I\n4 4\ncore is 0.163 eV for [PXZDBFDP] Cu I (HOMO→HOMO-2), which is more than doubled in\n2 4 4\ncomparison to that of [PhPXZDBFDP] Cu I (HOMO→HOMO-1).”\n2 4 4\n“……but also low-lying cluster-center (CC) components including metal-metal (MMCT) and metal-\ncounterion charge transfer (MXCT) inferior in radiation.”\n“Compared to [PhPXZDBFDP] Cu I with D-π-A type ligands and weakened LCT”\n2 4 4\nS17\nReviewer #3:\nThe manuscript entitled “Excited State Reversal in Copper Iodide Clusters Enables 100% Exciton\nRadiation” reported two new electroluminescent Cu I cubic clusters stabilized with phenoxazine (PXZ)\n4 4\nfunctionalized biphosphine ligands. This kind of new electroluminescent organic-inorganic hybrid\nmaterials emerged rapidly in recent years. As the authors emphasized, the excited states of cluster\nmolecules were multi-component, including non-radiative CC states and ligand-incorporated charge\ntransfer and locally excited states. The direct and energy transfer-induced populations of CC states were\nbelieved as the key issue inducing energy loss and efficiency reduction. Although there were many works\nreported the excited state engineering of cluster emitters, reversing the energy levels of CC states and\nligand centered excited states would be ideal to avert CC-induced quenching. In this work, through\nintroducing a strong PXZ donor in the D-A ligand, the so-called excited state reversal of\n[PXZDBFDP] Cu I cube was realized, leading to efficient dual emission with 52% TADF and 48%\n2 4 4\nphosphorescence (PH). The authors also prepared another cluster emitter [PhPXZDBFDP] Cu I with a\n2 4 4\nD-π-A ligand, which features the normal low-lying MC states. As a result, [PXZDBFDP] Cu I realized\n2 4 4\nthe state-of-the-art performance, e.g. PLQY of ~90%, and the maximum EQE as high as 35.5%, which is\nthe record-high value for EL homo-copper clusters. Although the maximum value of EL efficiencies for\n[PXZDBFDP]2Cu4I4 as the second high value reported so far was about 0.1% lower than the record, roll-\noffs of [PXZDBFDP] Cu I based device were markedly reduced. As a result, its efficiencies at 100 and\n2 4 4\n1000 nits are record high. This work not only breaks through the performance bottleneck of EL clusters,\nbut also provides a new and very important insight into excited state optimization for multi-component\nsystems. Therefore, this paper deserved to be published on Nature Communications after minor revision.\nResponse: Reviewer’s kind approval and accurate summary of our work is highly appreciated. Thanks a\nlot!\n1. To make the materials can be prepared by other groups, the comprehensive characterization of\nchemical structures should be modified. Some important evidences, such as NMR data and spectra,\nshould be added in supporting information.\nResponse: Thanks a lot for this constructive comment! The NMR data and spectra, as well as elementary\nanalysis results, were added in the experimental section of Supplementary Information. Thanks a lot!\nRevision:\nNMR data and spectra and elementary analysis data were added:\nS18\n“The chemical structures of all the compounds were fully characterized with NMR spectra, mass\nspectra and elemental analysis (Supplementary Figs 2-20).”\n“Elemental analysis for C48H33NO4P2: calculated: C, 76.90; H, 4.44; N, 1.85; found: C, 76.91; H,\n4.43; N, 1.85.”\n“Elemental analysis for C48H33NO2P2: calculated: C, 80.32; H, 4.63; N, 1.95; N, 1.85; found: C,\n80.31; H, 4.61; N, 1.93.”\n“Elemental analysis for C96H66Cu4I4N2O4P4: calculated: C, 52.48; H, 3.03; N, 1.27; found: C,\n52.49; H, 3.05; N, 1.24.”\n“Elemental analysis for C54H37NO4P2: calculated: C, 78.54; H, 4.52; N, 1.70; found: C, 78.55; H,\n4.53; N, 1.72.”\n“Elemental analysis for C54H37NO2P2: calculated: C, 81.70; H, 4.70; N, 1.76; found: C, 81.71; H,\n4.72; N, 1.77.”\n“13C NMR (TMS, CDCl , 100 MHz): δ = 160.71, 157.62, 149.34, 148.52, 141.87, 139.12, 139.06,\n3\n137.15, 136.98, 133.75, 133.46, 133.27, 131.78, 131.65, 131.19, 130.78, 129.82, 129.71, 127.92, 126.45,\n126.22, 126.18, 125.66, 125.61, 124.95, 124.89, 124.71, 119.54, 119.23, 118.47, 118.17 ppm. 31P NMR\n(TMS, CDCl , 162 MHz): δ = -29.913, -30.541 ppm. Elemental analysis for C108H74Cu4I4N2O4P4:\n3\ncalculated: C, 55.21; H, 3.17; N, 1.19; found: C, 55.21; H, 3.19; N, 1.17.”\nSupplementary Fig. 2. 1H NMR spectrum of PXZDBFDPO in CDCl .\nSupplementary Fig. 3. 1H NMR spectrum of PhPXZDBFDPO in CDCl .\nSupplementary Fig. 5. 31P NMR spectrum of PhPXZDBFDPO in CDCl .\nSupplementary Fig. 8. 1H NMR spectrum of PXZDBFDP in CDCl .\nSupplementary Fig. 12. 13C NMR spectrum of PXZDBFDP in CDCl .\n2 4 4 3\nS23\nSupplementary Fig. 15. 1H NMR spectrum of [PhPXZDBFDP] Cu I in DMSO.\n2 4 4\nSupplementary Fig. 16. 31P NMR spectrum of [PXZDBFDP] Cu I in CDCl .\n2 4 4 3\nSupplementary Fig. 17. 31P NMR spectrum of [PhPXZDBFDP] Cu I in CDCl .\n2 4 4 3\nS24\nSupplementary Fig. 18. 13C NMR spectrum of [PXZDBFDP] Cu I in CDCl .\n2 4 4 3\nSupplementary Fig. 19. 13C NMR spectrum of [PhPXZDBFDP] Cu I in CDCl .\n2 4 4 3\n2. Considering the importance of excited state reversal, besides Gaussian simulation results, can the\nauthors provide the experimental evidences to demonstrate such reversed excited states, e.g. the\nassignment of absorption peaks for CC and LC.\nResponse: Thanks a lot for this constructive comment! As reviewer pointed out, the absorption and\nexcitation spectra provide the direct experimental evidence of the reversed excited states for\n[PXZDBFDP] Cu I . Despite the similar absorptions in dilute solutions, the absorption spectra of neat\n2 4 4\n[PXZDBFDP] Cu I and [PhPXZDBFDP] Cu I films are totally different. It can be noted that in the\n2 4 4 2 4 4\nrange of 350-450 nm, [PXZDBFDP] Cu I exhibits a continuous but weak absorption tail, corresponding\n2 4 4\nto typical LCT absorption. On the contrary, in this range, the absorptions of [PhPXZDBFDP] Cu I are\n2 4 4\nS25\nmulti-peak and stronger than that of [PXZDBFDP] Cu I , which indicates the CC characteristics for the\n2 4 4\nformer. On the other hand, excitation spectra can also give the direct evidences about the contributions of\nthe excited states to radiation. The excitation spectra of [PXZDBFDP] Cu I and [PhPXZDBFDP] Cu I\n2 4 4 2 4 4\nreveal the similar MLCT bands peaked at ~320 and 335 nm, accompanied with CC bands as shoulder\npeaks at ~340 and 370 nm, respectively. Differently, in opposite to high-energy LCT band of\n[PhPXZDBFDP] Cu I at 275 nm, LCT band of neat [PXZDBFDP] Cu I film is the lowest energy band\n2 4 4 2 4 4\npeaked at ~400 nm, experimentally demonstrating the abnormal excited-state reversal and the resulted\nexothermic CC→LCT energy transfer through fast and efficient internal conversion.\nThe discussion was added in the related section. Thanks a lot!\nRevision:\nThe different origins of absorption bands for the clusters were added:\n“In absorption spectra of spin-coated neat films, besides ligands-attributed bands, intermolecular\ninteractions markedly enhance the charge transfer bands (Supplementary Fig. 26 and Supplementary\nTable 5). Nonetheless, it can be noted that CC band at 350-400 nm is predominant for\n[PhPXZDBFDP] Cu I , but [PXZDBFDP] Cu I exhibits more distinct LCT band at 350-450 nm.”\n2 4 4 2 4 4\n3. In neat film, [PhPXZDBFDP] Cu I had two peaks. Although according to the absorption and\n2 4 4\nexcitation spectra, the lowest excited states of [PhPXZDBFDP] Cu I would be CC state. However, the\n2 4 4\ndual-peak emissions of this cluster should be used to further demonstrate the excited-state evolution. So,\nthe transient investigation of CC and LC states should provide.\nResponse: Thanks a lot for this constructive comment! We should apologize for our unclear and\ninsufficient explanation. “Dual emission” of copper iodide clusters is originated from their\nmulticomponent excited states consisting of ligand-centered (LC) and cluster-centered (CC) components,\nrespectively corresponding to high-energy (HE) and low-energy (LE) emission bands (please see Figure\nR1, J. Am. Chem. Soc. 1991, 113, 2954-2965), in which LC components are composed of metal-ligand\ncharge transfer (MLCT) and intra- and inter-ligand charge transfer (LCT) states, primarily involving in\nCu-I bond lengthening and Cu-P bond shortening; while, CC components feature d-d transitions,\nprimarily involving contraction and deformation of the Cu I core (Acc. Chem. Res. 1993, 26, 220-226).\n4 4\nThis distinct geometrical reorganization effectively separates the potential energy surfaces of LC and CC\nstates in configurational space. Therefore, internal transitions from the HE bands to the LE bands are\nS26\nspatially forbidden to induce the extremely slow transition rates between them, resulting in the\nindependent observation of HE and LE bands, namely dual emission (Chem. Rev.1999, 99, 3625-3647).\nTDDFT simulation shows that the excited states of [PhPXZDBFDP] Cu I are also localized on its\n2 4 4\ncoordination skeleton, which are composed of LC and CC components, corresponding to HE and LE\nbands. Since its excited-state characteristics are highly similar to the previous reports of Cu I cubes,\n4 4\n[PhPXZDBFDP] Cu I exhibits typical temperature-sensitive dual emission (Figure R1c). Nonetheless,\n2 4 4\nwe agree with reviewer’s opinion that a direct evidence from transient emission behavior should be more\ncogent. Therefore, according to reviewer's suggestion, we further investigate the time-resolved emission\nspectra of [PhPXZDBFDP] Cu I (Supplementary Figure 31). It shows that after excitation, the HE and\n2 4 4\nLE bands appear at the same time, which further demonstrates the blocked transitions between them.\nWith the passage of time, the intensities of HE and LE bands simultaneously decrease, but the tendency\nof HE band is faster, due to the shorter lifetime. So, in accord with previous reports, for\n[PhPXZDBFDP] Cu I , transitions between its LC and CC bands are basically limited.\n2 4 4\n[FIGURE REDACTED]\nFigure R1. (a-c) The structures and PL spectra of representative Cu I cubes featuring two emission\n4 4\nbands; (d) Structure and temperature dependent PL spectra of [PhPXZDBFDP] Cu I in our work.\n2 4 4\nThe related description and explanation were added in the revision, as well as Supplementary Figure\n31. Thanks a lot\nS27\nRevision:\nExplanations of two emission bands from [PhPXZDBFDP] Cu I and transition behavior were\n2 4 4\nadded:\n“In contrast, neat [PhPXZDBFDP] Cu I film reveals two emission peaks at 522 and 626 nm\n2 4 4\noriginated from its high-energy MLCT and low-energy CC states with different geometrical\nreorganization,49, 50 which is similar to donor-free [DBFDP] Cu I in accord to their identical CC-featured\n2 4 4\nS and T states.22, 39”\n1 1\n49. Kyle KR, Ryu CK, Ford PC, DiBenedetto JA. Photophysical studies in solution of the\ntetranuclear copper(I) clusters Cu4I4L4 (L = pyridine or substituted pyridine). J Am Chem Soc113, 2954-\n2965 (1991).\n50. Ford PC, Vogler A. Photochemical and photophysical properties of tetranuclear and hexanuclear\nclusters of metals with d10 and s2 electronic configurations. Acc Chem Res26, 220-226 (1993).\nSupplementary Figure 31. Sliced time-resolved emission spectra of neat [PhPXZDBFDP] Cu I film at\n2 4 4\n0.5, 1.0, 5.0, 20.0, 50.0 and 100.0 µs. HE and LE refer to “high-energy” and “low-energy” bands.\n4. I noticed that PL and EL spectra of [PhPXZDBFDP] Cu I were completely different, therefore, a\n2 4 4\nmore detailed explanation on the stronger long-wavelength band in EL spectra should be added. As the\nother side of the coin, why were PL and EL spectra for [PXZDBFDP] Cu I the same? In addition, some\n2 4 4\nreferences on TADF and PH of Cu-clusters should be cited into the paper, for example,\n10.31635/ccschem.022.202101741, Nature Communications, 2024, 15, 9401 (PH properties of Cu-NCs),\nCCS Chem., 2024, 6, 2537 (TADF properties of Cu-NCs), etc.\nS28\nResponse: Thanks a lot for this constructive comment! We should apologize for our insufficient\nexplanation. The difference between PL and EL spectra of [PhPXZDBFDP] Cu I is attributed to\n2 4 4\ndifferent mechanisms of photo-excitation and electro-excitation. As reviewer pointed out, compared to PL\nspectrum of BCPO:20% [PhPXZDBFDP] Cu I , its EL spectrum was red-shifted and broadened, due to a\n2 4 4\nnew emission band at 600 nm, which can be attributed to 3CC radiation. Actually, in our previous work\npublished in Chem. Mater. 2017, 29, 6606, we reported the similar phenomenon from the parent cluster\nmolecule [DBFDP] Cu I , whose EL spectra exhibited enhanced orange bands attributed to 3CC state,\n2 4 4\nmaking EL emission become white rather than sky blue for its PL emission (Figure R2). Under photo-\nexcitation, most excitons are singlet rather than triplet, because of the spin forbidden feature for the latter.\nOn the contrary, under electricity field, the singlet/triplet ratio is 1/3, according to spin statistics. Since\n3CC state is triplet, in EL process, the population of 3CC state is markedly increased, inducing stronger\n3CC-attributed long-wavelength emission bands. The situation of [PhPXZDBFDP] Cu I based devices is\n2 4 4\nthe same, since the electron configurations of its excited states are almost identical to [DBFDP] Cu I .\n2 4 4\nFigure R2. Comparison on PL and EL spectra of [PhPXZDBFDP] Cu I and its parent cluster\n2 4 4\n[DBFDP] Cu I .\n2 4 4\nThe related explanation was added in the revision. The references 54-56 were also added in the\ncitation. Thanks a lot!\nRevision:\nExplanation on difference between PL and EL spectra for [PhPXZDBFDP] Cu I was added:\n2 4 4\n“Through dual-peak fitting, it is clear that different to photo-excitation, because of the statistical\nmajority of electro-generated triplet excitons, the population of 3CC state for [PhPXZDBFDP] Cu I is\n2 4 4\nS29\nmarkedly increased in EL process, rendering markedly enhanced long-wavelength emission and thereby\nworsening exciton quenching.39”\n“39. Xie M, Han C, Zhang J, Xie G, Xu H. White Electroluminescent Phosphine-Chelated\nCopper Iodide Nanoclusters. Chem Mater29, 6606-6610 (2017).”\n“54. Fan X, et al. Structural Isomerization in Cu(I) Clusters: Tracing the Cu Thermal\nMigration Paths and Unveiling the Structure-Dependent Photoluminescence. CCS Chem 5, 350-360\n(2023).”\n“55. Deng C-L, et al. Hierarchical Homochiral Assembly of Polyhedral Cage-Type\nNanoclusters. CCS Chem6, 2537-2548 (2024).”\n“56. Zhao Z-H, et al. Buckling cluster-based H-bonded icosahedral capsules and their\npropagation to a robust zeolite-like supramolecular framework. Nat Commun 15, 9401-9410 (2024).”\nS30\nReviewer #4:\nThis manuscript reports the study of two molecular copper iodide clusters as emitters for light-emitting\ndiodes applications. By employing a ligand engineering strategy based on the increase of the donor-\nacceptor effect, change of the relative energy of the excited states was achieved that favors exciton\nradiation. A high value of EL external quantum efficiency is thus reported for the studied compounds, that\nis the record for cluster-based LED. Although this approach has already been investigated by the authors\nwith chemically close compounds (Angew. Chem. 2023 e202305018, ref.51), a record is established\npromoting the interest of the domain. The comparison of the two clusters having slightly different ligands,\nis very informative, the work is well conducted and the results are convincing. For these reasons, this\nwork can be recommended for publication in Nature Communications, providing the following points are\ntaken into account.\nResponse: We are very grateful to Reviewer’s kind approval and brief summary of our work. Thanks a lot!\n1. The elemental analyses of the two clusters are missing.\nResponse: Thanks a lot for this constructive comment! We should apologize for our carelessness during\nmanuscript preparation. The elemental analysis data were added in the Supplementary Information.\nThanks a lot!\nRevision:\nElementary analysis data were added:\n“Elemental analysis for C48H33NO4P2: calculated: C, 76.90; H, 4.44; N, 1.85; found: C, 76.91; H,\n4.43; N, 1.85.”\n“Elemental analysis for C48H33NO2P2: calculated: C, 80.32; H, 4.63; N, 1.95; N, 1.85; found: C,\n80.31; H, 4.61; N, 1.93.”\n“Elemental analysis for C96H66Cu4I4N2O4P4: calculated: C, 52.48; H, 3.03; N, 1.27; found: C,\n52.49; H, 3.05; N, 1.24.”\n“Elemental analysis for C54H37NO4P2: calculated: C, 78.54; H, 4.52; N, 1.70; found: C, 78.55; H,\n4.53; N, 1.72.”\n“Elemental analysis for C54H37NO2P2: calculated: C, 81.70; H, 4.70; N, 1.76; found: C, 81.71; H,\n4.72; N, 1.77.”\n“Elemental analysis for C108H74Cu4I4N2O4P4: calculated: C, 55.21; H, 3.17; N, 1.19; found: C,\n55.21; H, 3.19; N, 1.17.”\nS31\n2. The 31P NMR data of [PhPXZDBFDP] Cu I are missing.\n2 4 4\nResponse: Thanks a lot for this constructive comment! We should apologize for our carelessness during\nmanuscript preparation. The 31P MNR data, as well as all NMR spectra, were added in the Supplementary\nInformation. Thanks a lot!\nRevision:\nNMR data were added:\n“13C NMR (TMS, CDCl , 100 MHz): δ = 160.71, 157.62, 149.34, 148.52, 141.87, 139.12, 139.06,\n3\n137.15, 136.98, 133.75, 133.46, 133.27, 131.78, 131.65, 131.19, 130.78, 129.82, 129.71, 127.92, 126.45,\n126.22, 126.18, 125.66, 125.61, 124.95, 124.89, 124.71, 119.54, 119.23, 118.47, 118.17 ppm. 31P NMR\n(TMS, CDCl , 162 MHz): δ = -29.913, -30.541 ppm.”\nSupplementary Fig. 3. 1H NMR spectrum of PhPXZDBFDPO in CDCl .\nSupplementary Fig. 6. 13C NMR spectrum of PXZDBFDPO in CDCl .\nSupplementary Fig. 9. 1H NMR spectrum of PhPXZDBFDP in CDCl .\nSupplementary Fig. 12. 13C NMR spectrum of PXZDBFDP in CDCl .\n2 4 4 3\nS36\nSupplementary Fig. 15. 1H NMR spectrum of [PhPXZDBFDP] Cu I in DMSO.\n2 4 4\nSupplementary Fig. 16. 31P NMR spectrum of [PXZDBFDP] Cu I in CDCl .\n2 4 4 3\nSupplementary Fig. 17. 31P NMR spectrum of [PhPXZDBFDP] Cu I in CDCl .\n2 4 4 3\nS37\nSupplementary Fig. 18. 13C NMR spectrum of [PXZDBFDP] Cu I in CDCl .\n2 4 4 3\nSupplementary Fig. 19. 13C NMR spectrum of [PhPXZDBFDP] Cu I in CDCl .\n2 4 4 3\n3. Line 16 page 4, HOMO+1 and HOMO+2 should be corrected by HOMO-1 and HOMO-2.\nResponse: Thanks a lot for this constructive comment! We should apologize for our carelessness during\nmanuscript preparation. The manuscript was rechecked carefully to try our best to get rid of typos and\ngrammar errors. Thanks a lot!\nRevision:\nTypos and grammar errors were corrected:\nS38\n“In this sense, both the singlet and triplet LCT states of [PXZDBFDP] Cu I nearly equally\n2 4 4\ncontraibute to PH and TADF under a dual-emission mode, which can simultaneously reduce exciton-\naccumulation induced quenching and accelerate radiation.”\n“On the contrary to the situation of [PhPXZDBFDP] Cu I , the HOMO-1 and HOMO-2 of\n2 4 4\n[PXZDBFDP] Cu I are respectively contributed by PXZ and Cu I core, reflecting the stronger D-A\n2 4 4 4 4\ninteractions. Consequently, [PXZDBFDP] Cu I exhibits the shallower HOMO and deeper lowest\n2 4 4\nunoccupied molecular orbital (LUMO), compared to [PhPXZDBFDP] Cu I , which are consistent with\n2 4 4\nthe HOMO and LUMO energy levels of -5.46 and -3.01 eV and -5.50 and -2.84 eV experimentally\nestimated with cyclic voltammetry (CV) analysis (Supplementary Fig. 22 and 23 and Supplementary\nTable 5). Furthermore, the energy gap between the highest occupied molecular orbitals on PXZ and Cu I\n4 4\ncore is 0.163 eV for [PXZDBFDP] Cu I (HOMO→HOMO-2), which is more than doubled in\n2 4 4\ncomparison to that of [PhPXZDBFDP] Cu I (HOMO→HOMO-1).”\n2 4 4\n“……but also low-lying cluster-center (CC) components including metal-metal (MMCT) and metal-\ncounterion charge transfer (MXCT) inferior in radiation.”\n“Compared to [PhPXZDBFDP] Cu I with D-π-A type ligands and weakened LCT”\n2 4 4\n4. The SCXRD analysis should be clearly mentioned in the text and the crystallographic data\nprovided in the SI.\nResponse: Thanks a lot for this constructive comment! The SCXRD analysis details and data were added\nin the Supplementary Information. Thanks a lot!\nRevision:\nSCXRD details were add:\n“The crystals suitable for single-crystal XRD analysis were obtained through slowly diffusing ether\ninto dichloromethane solution of the clusters at room temperature. All diffraction data were collected at\nradiation in ω scan mode. All structures were solved by direct method and difference Fourier syntheses.\nNon-hydrogen atoms were refined by full-matrix least-squares techniques on F2 with anisotropic thermal\nparameters. The hydrogen atoms attached to carbons were placed in calculated positions with C−H = 0.93\nÅ and U (H) = 1.2Ueq (C) in the riding model approximation. All calculations were carried out with the\nSHELXL97 program.”\nS39\nSupplementary Fig. 20. Coordination geometries of [PXZDBFDP] Cu I and [PhPXZDBFDP] Cu I , in\n2 4 4 2 4 4\nwhich atom numbers were highlighted in accord with Supplementary Table 1-4.\nSupplementary Table 1. The selected bond lengths (Å) of [PXZDBFDP] Cu I single crystal.\n2 4 4\nCu1- Cu2 2.738 Cu1- I1 2.690\nCu1- I2 2.698 Cu1- I3 2.720\nCu1- P1 2.244 Cu2- I1 2.724\nCu2- I2 2.704 Cu2- I4 2.662\nCu2- P2 2.253 Cu3- Cu4 2.738\nCu3- I2 2.662 Cu3- I3 2.724\nCu3- I4 2.704 Cu3- P3 2.252\nCu4- I1 2.704 Cu4- I3 2.688\nCu4- I4 2.698 Cu4- P4 2.243\nSupplementary Table 2. The selected bond angles (o) of [PXZDBFDP] Cu I single crystal.\n2 4 4\nI1- Cu1- I2 119.41 I1- Cu1- I3 98.98\nI1- Cu1- P1 114.83 I1- Cu2- I2 117.98\nI1- Cu2- I4 107.47 I1- Cu2- P2 109.23\nI1- Cu4- I3 98.96 I1- Cu4- Cu3 109.11\nI1- Cu4- I4 106.51 I1- Cu4- P4 114.91\nI2- Cu1- P1 102.40 I2- Cu1- I3 106.56\nI2- Cu2- P2 107.48 I2- Cu2- I4 101.37\nI2- Cu3- P3 113.31 I2- Cu3- I3 107.45\nI2- Cu3- I4 101.35 I2- Cu3- Cu4 112.24\nS40\nI3- Cu1- P1 114.95 I3- Cu1- Cu2 109.12\nI3- Cu3- P3 109.25 I3- Cu3- Cu4 58.94\nI3- Cu3- I4 117.95 I3- Cu4- I4 119.43\nI3- Cu4- Cu3 60.25 I3- Cu4- P4 114.89\nI4- Cu2- P2 113.27 I4- Cu2- Cu1 112.24\nI4- Cu3- Cu4 59.44 I4- Cu3- P3 107.48\nI4- Cu4- Cu3 59.65 I4- Cu4- P4 102.42\n5. The emission spectra of [PhPXZDBFDP] (100%) in Figures 2a and S7 are not really consistent.\nThe two emission bands are clearly less resolved in Figure S7. The moderate temperature change of the\nCC band is different from the classical thermochromic effect for these clusters. The authors should\ndiscuss this point.\nResponse: Thanks a lot for this constructive comment! We should apologize for our carelessness in\nconsistence of sample preparation and measurement. The difference in PL spectra for neat\n[PhPXZDBFDP] Cu I film in Figure 2a and Supplementary Figure 27b was induced by the different film\n2 4 4\npreparation recipes. The thickness of the film used for temperature dependence of PL spectra was only a\nhalf of that used for Figure 2a, weakening 3CC emission. Therefore, we re-prepared the thinker film and\nre-measured the spectra, which show the remarkable changes from HE bands to LE bands along with\ntemperature decreasing (Figure R1d).\nWe also should apologize for our unclear and insufficient explanation. As reviewer pointed out, there\nwere many copper iodide clusters exhibited “dual emission”, which is originated from their\nmulticomponent excited states consisting of ligand-centered (LC) and cluster-centered (CC) components,\nrespectively corresponding to high-energy (HE) and low-energy (LE) emission bands (please see Figure\nR1, J. Am. Chem. Soc. 1991, 113, 2954-2965), in which LC components are composed of metal-ligand\ncharge transfer (MLCT) and intra- and inter-ligand charge transfer (LCT) states, primarily involving in\nCu-I bond lengthening and Cu-P bond shortening; while, CC components feature d-d transitions,\nprimarily involving contraction and deformation of the Cu I core (Acc. Chem. Res. 1993, 26, 220-226).\n4 4\nThis distinct geometrical reorganization effectively separates the potential energy surfaces of LC and CC\nstates in configurational space, making internal transitions from the HE bands to the LE bands spatially\nforbidden to induce the extremely slow transition rates between them, resulting in the independent\nobservation of HE and LE bands, namely dual emission (Chem. Rev. 1999, 99, 3625-3647). It shows that\nexcited-state structure distortion is the key factor influencing not only the intensities but also peak\nwavelengths of the dual emissions. Therefore, most of Cu I cubes with distinct dual emissions reported\n4 4\nS41\nso far were based on mono-dentate ligands, which formed relatively soft coordination configurations.\nNonetheless, the differences between two peaks for all-conjugated ligands based clusters (Figures R1a\nand R1c) were still larger than aliphatic ligand based analog (Figure R1b).\nTDDFT simulation shows that the excited states of [PhPXZDBFDP] Cu I are also localized on its\n2 4 4\ncoordination skeleton, which are composed of LC and CC components, corresponding to HE and LE\nbands. Since its excited-state characteristics are highly similar to the previous reports of Cu I cubes,\n4 4\n[PhPXZDBFDP] Cu I exhibits typical temperature-sensitive dual emission (Figure R1d). In contrast,\n2 4 4\nPhPXZDBFDP is a bidentate ligand, making [PhPXZDBFDP] Cu I have much higher rigidity; therefore,\n2 4 4\nits excited-state structural distortion is markedly limited, further decreasing the peak wavelength\ndifferences of its two emissions and making such dual emission become not so distinct in comparison to\nother mono-dentate ligands based Cu I clusters. According to reviewer's suggestion, we further\n4 4\ninvestigate the time-resolved emission spectra of [PhPXZDBFDP] Cu I (Supplementary Figure 31). It\n2 4 4\nshows that after excitation, the HE and LE bands appear at the same time, which further demonstrates the\nblocked transitions between them. With the passage of time, the intensities of HE and LE bands\nsimultaneously decrease, but the tendency of HE band is faster, due to the shorter lifetime.\n[FIGURE REDACTED]\nFigure R1. (a-c) The structures and PL spectra of representative Cu I cubes featuring two emission\n4 4\nbands; (d) Structure and temperature dependent PL spectra of [PhPXZDBFDP] Cu I in our work.\n2 4 4\nThe related description and explanation were added in the revision, as well as Supplementary Figures\n27 and 31. Thanks a lot\nS42\nRevision:\nExplanations of two emission bands from [PhPXZDBFDP] Cu I and transition behavior were\n2 4 4\nadded:\n“PL spectra of neat [PXZDBFDP] Cu I are nearly independent on temperature. But, neat\n2 4 4\n[PhPXZDBFDP] Cu I film shows the remarkable changes from HE to LE bands along with temperature\n2 4 4\ndecreasing, attributed to the radiation shift from ligand-center excited states to CC states, which is\nconsistent with the typical thermochromic behavior similar to previous reports of mono-dentate ligands\nbased copper iodide clusters.”\nSupplementary Fig. 27. PL spectra of neat films based on (a) [PXZDBFDP] Cu I and (b)\n2 4 4\n[PhPXZBFDP] Cu I at different temperatures.\n2 4 4\nSupplementary Fig. 31. Sliced time-resolved emission spectra of neat [PhPXZDBFDP] Cu I film at 0.5,\n2 4 4\n1.0, 5.0, 20.0, 50.0 and 100.0 µs. HE and LE refer to “high-energy” and “low-energy” bands.\nS43\n6. Only one cycle of cyclic voltammetry is presented in Figure S3 for each cluster. The authors\nshould mention if there is degradation after multiple cycles.\nResponse: Thanks a lot for this constructive comment! We agree with reviewer’s opinion that\nelectrochemical stability of the emitters is important for electroluminescent applications. Therefore,\naccording to reviewer’s suggestion, we measured multicycle voltammograms of [PXZDBFDP] Cu I and\n2 4 4\n[PhPXZDBFDP] Cu I . It shows that for both clusters, after ten redox cycles, the changes of the peaks\n2 4 4\nand peak areas are limited, indicating their good electrochemical stability and the unchanged chemical\nstructures under bias.\nThe related descriptions and Supplementary Fig. 23 were added. Thanks a lot!\nRevision:\nMulticycle voltammograms and related description were added:\n“Multicycle voltammograms of [PXZDBFDP] Cu I and [PhPXZDBFDP] Cu I were measured,\n2 4 4 2 4 4\nwhich shows that during ten redox cycles, the changes of the peak potentials and peak areas are limited,\nindicating their good electrochemical stability and the unchanged chemical structures under electrical\nfield.”\nSupplementary Fig. 23. Electrochemical stabilities of [PXZDBFDP] Cu I and [PhPXZBFDP] Cu I\n2 4 4 2 4 4\nevaluated with multicycle voltammograms at room temperature with the scanning rate of 100 mV s-1.\nS44\nResponses to Reviewers’ Comments\nReviewer #1:\nThe authors have provided detailed responses and made improvements to this work. However, one issue\nremains unresolved: even if Supplementary Figure 27b has been redrawn, it is still essential to clarify why\nthe thickness of [PhPXZDBFDP] Cu I films has such a significant effect on the corresponding\n2 4 4\nphotoluminescence spectra.\nResponse: We are very grateful to reviewer for the kind approval of our efforts in the first revision.\nThanks a lot!\nWe should apologize for our unclear explanation about the different PL spectrum of\n[PhPXZDBFDP] Cu I neat film at 300 K in Supplementary Figure 27b. The emission intensity ratios of\n2 4 4\nhigh-energy and low-energy bands of a typical dual-emissive Cu I cluster are highly dependent on\n4 4\nintermolecular interactions. Since metallic cores are embedded in ligands, intermolecular interactions\nmainly have effects on ligand-centered excited states. Therefore, in aggregation states, the emissions from\nthe ligand-centered high-energy excited states are mainly quenched; in turn, the emissions from the 3CC\nstates become relative stronger, corresponding to a typical chromic process based on morphological\nchange (Chem. Soc. Rev. 2021, 50, 4606-4628).\nActually, in the original Supplementary Figure 7b, the so-called neat [PhPXZDBFDP] Cu I film\n2 4 4\nfor measurement was prepared from a solution with too low concentration of only 10-6 mol L-1, which was\nactually used for optical measurement of dilute solutions. This concentration was about 0.0001 of the\ncorrect value (10 mg mL-1, 10-2 mol L-1). Based on such low concentration of 10-6 mol L-1, it is impossible\nto form the uniform and continuous films on the substrates, rendering the poor aggregation in the so-\ncalled “film”. However, strong intermolecular interactions in neat [PhPXZDBFDP] Cu I film mainly\n2 4 4\noccur between adjacent ligands, therefore quenching emissions from ligand-centered excited state, and in\nturn making CC band predominant. Thus, compared to PL spectrum of really neat [PhPXZDBFDP] Cu I\n2 4 4\nfilm in Figure 2a, PL spectra in the original Supplementary Figure 7b mainly contain emission bands at\n~500 nm, which are almost identical to PL spectrum of 20% [PhPXZDBFDP] Cu I doped film ascribed\n2 4 4\nto ligand-centered excited states, accompanied with nearly negligible 3CC bands.\nIn the first revision, because of our carelessness, despite the correct solution concentration of 10\nmg mL-1, we inappropriately adopted dip coating to prepare the neat film. Although the film thickness\nwould be acceptable, the film is still not uniform, inducing the unsmooth spectral profiles. In this second\nS1\nrevision, we further used spin coating technology to prepare the uniform and homogeneous neat\n[PhPXZDBFDP] Cu I film, whose PL spectra show smoother profiles.\n2 4 4\nThe revised Supplementary Figure 27b was added in the revision. Thanks a lot!\nRevision:\nTemperature dependent PL spectra of spin-coated neat [PhPXZDBF] Cu I film were remeasured\n2 4 4\nand added, as well as the related discussions:\n“PL spectra of neat [PXZDBFDP] Cu I are nearly independent on temperature. But, neat\n2 4 4\n[PhPXZDBFDP] Cu I film shows the remarkable changes from HE to LE bands along with temperature\n2 4 4\ndecreasing, attributed to the radiation shift from ligand-center excited states to CC states, which is\nconsistent with the typical thermochromic behavior similar to previous reports of mono-dentate ligands\nbased copper iodide clusters.”\nSupplementary Fig. 27. PL spectra of spin-coated neat films based on (b) [PhPXZBFDP] Cu I in\n2 4 4\ntemperature range of 20-300 K.\nS2\nReviewer #4:\nThe authors have revised their article in accordance to the suggestions which improves its quality. Despite\nsome points that have to be taken into account, as detailed below, the article can be recommended for\npublication in Nature Communications.\n1-3- OK for the additional data.\nResponse: Reviewer’s kind approval and accurate summary of our work are highly appreciated. Thanks a\nlot!\n4. In addition to the geometric data of the molecular structures (Fig. 20 and Tables 1-4 in SI), the\ncrystal data (space group, cell parameters, …) and structure refinements data of the SCXRD analysis\nshould also be reported in the SI.\nResponse: Thanks a lot for this constructive comment! We should apologize for our carelessness in data\npresentation. According to Reviewer’s suggestion, the crystal data and structure refinement were added in\nthe supplementary information as Supplementary Table 1. Thanks a lot!\nRevision:\nSupplementary Table 1. Crystal data and structure parameters for the clusters.\n[PXZDBFDP] Cu I [PhPXZDBFDP] Cu I\n2 4 4 2 4 4\nEmpirical formular C H Cu I N O P C H O N P Cu I\n96 66 4 4 2 4 4 108 74 4 2 4 4 4\nFormular weight 2197.14 2349.480\nCrystal systems Monoclinic Triclinic\nSpace group C 2/c P ī\na(Å) 31.955(6) 17.2039(15)\nb(Å) 12.944(2) 19.3511(16)\nc(Å) 25.931(5) 22.1851(16)\nα (˚) 90 84.691(4)\nβ (˚) 112.989(5) 79.679(4)\nγ (˚) 90 70.009(4)\nV (Å) 9874(3) 6824.5(10)\nZ 4 2\nρ (g/cm3) 1.478 1.394\ncalcd\nμ (mm–1) 2.212 1.620\nF(000) 4304.0 2848.0\nS3\nR [a] [I > 2σ (I)] 0.0516 0.0548\n1\nwR [b] (all data) 0.1189 0.1527\naR = ||F | – |F ||/|F |; wR = [[w (F 2 – F 2)2]/[ w (F 2)2]]1/2.\n1 o c o 2 o c o\n5. The discrepancy in the emission spectra of [PhPXZDBFDP] (100%) in Figures 2a and S7 (old\none), is attributed to the different film thickness. I don’t understand how the thickness can impact the CC\nemission in the PL measurement, please clarify. The new spectra reported in Fig S27 are very noisy\ncompared with those on Fig. 2. Are all spectra in Fig. 2a (and Fig S6,) fits (fitting) of experimental curves?\nThe authors should consider to record data with better S/N. The adjective ‘remarkable’ to describe the HE\nand LE bands variation observed is somewhat exaggerated.\nResponse: Thanks a lot for this constructive comment! We should apologize for our unclear explanation\nabout the different PL spectrum of [PhPXZDBFDP] Cu I neat film at 300 K in Supplementary Figure\n2 4 4\n27b. The emission intensity ratios of high-energy and low-energy bands of a typical dual-emissive Cu I\n4 4\ncluster are highly dependent on intermolecular interactions. Since metallic cores are embedded in ligands,\nintermolecular interactions mainly have effects on ligand-centered excited states. Therefore, in\naggregation states, the emissions from the ligand-centered high-energy excited states are mainly quenched;\nin turn, the emissions from the 3CC states become relative stronger, corresponding to a typical chromic\nprocess based on morphological change (Chem. Soc. Rev. 2021, 50, 4606-4628).\nActually, in the original Supplementary Figure 7b, the so-called neat [PhPXZDBFDP] Cu I film\n2 4 4\nfor measurement was prepared from a solution with too low concentration of only 10-6 mol L-1, which was\nactually used for optical measurement of dilute solutions. This concentration was about 0.0001 of the\ncorrect value (10 mg mL-1, 10-2 mol L-1). Based on such low concentration of 10-6 mol L-1, it is impossible\nto form the uniform and continuous films on the substrates, rendering the poor aggregation in the so-\ncalled “film”. However, strong intermolecular interactions in neat [PhPXZDBFDP] Cu I film mainly\n2 4 4\noccur between adjacent ligands, therefore quenching emissions from ligand-centered excited state, and in\nturn making CC band predominant. Thus, compared to PL spectrum of really neat [PhPXZDBFDP] Cu I\n2 4 4\nfilm in Figure 2a, PL spectra in the original Supplementary Figure 7b mainly contain emission bands at\n~500 nm, which are almost identical to PL spectrum of 20% [PhPXZDBFDP] Cu I doped film ascribed\n2 4 4\nto ligand-centered excited states, accompanied with nearly negligible 3CC bands.\nIn the first revision, because of our carelessness, despite the correct solution concentration of 10\nmg mL-1, we inappropriately adopted dip coating to prepare the neat film. Although the film thickness\nwould be acceptable, the film is still not uniform, inducing the unsmooth and even noisy spectral profiles.\nIn this second revision, we further used spin coating technology to prepare the uniform and homogeneous\nS4\nneat [PhPXZDBFDP] Cu I film, whose PL spectra show smoother profiles. The PL spectra at 300 K in\n2 4 4\nboth Supplementary Fig. 27b and Fig. 2a are almost identical, with respect to smoothness, locations and\nprofiles. We also should apologize for our unclear description of dual-peak fitting in the caption of Fig. 2a.\nPL spectrum of neat [PhPXZDBFDP] Cu I film in Fig. 2a is the experimental result, which is dual-peak\n2 4 4\nfitted to divided into two bands corresponding to emissions from MLCT and CC states. The description in\nthe caption of Fig. 2a was revised to improve clarity.\nThe revised Supplementary Figure 27b was added in the revision, as well as the related discussion.\nThanks a lot!\nRevision:\nTemperature dependent PL spectra of spin-coated neat [PhPXZDBF] Cu I film were remeasured\n2 4 4\nand added, as well as the related discussions:\n“PL spectra of neat [PXZDBFDP] Cu I are nearly independent on temperature. But, neat\n2 4 4\n[PhPXZDBFDP] Cu I film shows the remarkable changes from HE to LE bands along with temperature\n2 4 4\ndecreasing, attributed to the radiation shift from ligand-center excited states to CC states, which is\nconsistent with the typical thermochromic behavior similar to previous reports of mono-dentate ligands\nbased copper iodide clusters.”\n“PL spectrum of neat [PhPXZDBFDP] Cu I film is fitted with dual peaks corresponding to MLCT\n2 4 4\nand CC transitions, respectively highlighted with green and red fill colors;”\nSupplementary Fig. 27. PL spectra of spin-coated neat films based on (b) [PhPXZBFDP] Cu I in\n2 4 4\ntemperature range of 20-300 K.\nS5\n6. Regarding the cyclic voltammetry, the experimental conditions must be provided in SI. After\nmultiple cycles, the changes in the peak’s positions are quite significant and not limited as mentioned.\nPXZDBFDP cluster appears even less reproducible than PhPXZDBFDP cluster. The authors should give\nan explanation.\nResponse: Thanks for this constructive comment! We should apologize for the insufficient and inaccurate\nCV data and discussions. CV curves were measured with an Eco Chemie B. V. AUTOLAB potentiostat\nin a typical three-electrode cell, which contains a platinum sheet working electrode, a platinum wire\ncounter electrode and a silver/silver chloride (Ag/AgCl) reference electrode. Tetrabutylammonium\nhexafluorophosphate was used as electrolyte with a concentration of 0.1 mol L-1. All electrochemical\nexperiments were carried out under a nitrogen atmosphere at room temperature. Dichloromethane and\ntetrahydrofuran were used as solvents for oxidation and reduction, respectively, to provide enough\nwindows. The scanning rate was 100 mV s-1.\nTo investigate the electrochemical stability of the clusters, the redox circles were repeated for ten\ntimes, which were provided as Supplementary Fig. 23. In the last revision, as reviewer pointed out, the\nredox peaks of the clusters were shifted during multicyclic voltammetrical measurement. We think the\nvariations should be attributed to irreversibility induced by over oxidation and reduction. Therefore, we\nremeasured multicyclic voltammograms with limited bias ranges to repeat the first oxidation and\nreduction peaks, which show that both clusters are actually electrochemically stable.\nExperimental details, related discussions and Supplementary Fig. 23 were revised. Thanks a lot!\nRevision:\nExperimental conditions for cyclic voltammetry have been added:\n“Cyclic voltammetric (CV) studies were conducted using an Eco Chemie B. V. AUTOLAB\npotentiostat in a typical three-electrode cell with a platinum sheet working electrode, a platinum wire\ncounter electrode and a silver/silver chloride (Ag/AgCl) reference electrode. Tetrabutylammonium\nhexafluorophosphate was used as electrolyte with a concentration of 0.1 mol L-1. All electrochemical\nexperiments were carried out under a nitrogen atmosphere at room temperature.”\n“Multicycle voltammograms of [PXZDBFDP] Cu I and [PhPXZDBFDP] Cu I were measured,\n2 4 4 2 4 4\nwhich shows that during ten redox cycles, the changes of the peak potentials and peak areas are limited,\nindicating their good electrochemical stability and the unchanged chemical structures during redox\nprocesses.”\nS6\nSupplementary Fig. 23. Electrochemical stabilities of [PXZDBFDP] Cu I and [PhPXZBFDP] Cu I\n2 4 4 2 4 4\nevaluated with multicyclic voltammograms at room temperature with a scanning rate of 100 mV s-1.\nS7\nResponses to Reviewers’ Comments\nReviewer #1:\nI see the authors provide detailed description about the PL spectrum discrepancy in the first and second\nversion. I support the publication of revised manuscript in Nature Communications.\nResponse: We are very grateful to reviewer for the kind approval of our efforts in the evision. Thanks a\nlot!\nReviewer #4:\nThe authors have provided convincing explanations and new data regarding issues related to film\nemission discrepancy and the reversibility of cyclic voltammograms. The article can therefore be\nrecommended for publication in Nature Communications.\nResponse: Reviewer’s kind approval and accurate summary of our revisions are highly appreciated.\nThanks a lot!\nS1"}, {"round": 2, "reviewer_comments": {"reviewer_1": "I see the authors provide detailed description about the PL spectrum discrepancy in the first and second version. I support the publication of revised manuscript in Nature Communications.", "reviewer_4": "The authors have provided convincing explanations and new data regarding issues related to film emission discrepancy and the reversibility of cyclic voltammograms. The article can therefore be recommended for publication in Nature Communications."}, "author_response": ""}]

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