# Diversity of supramolecular assemblies based on photoactive Cu(I) trimetallic building blocks and N donor ditopic ligands: from 1D coordination polymers to metallacycles

Adrien Schlachter, Jaison Casas, Vincent Dorcet, Guillaume Calvez, Sylvie Ferlay, Christophe Lescop

► To cite this version:

Adrien Schlachter, Jaison Casas, Vincent Dorcet, Guillaume Calvez, Sylvie Ferlay, et al.. Diversity of supramolecular assemblies based on photoactive Cu(I) trimetallic building blocks and N donor ditopic ligands: from 1D coordination polymers to metallacycles. Inorganic Chemistry Frontiers, 2025, 12 (24), pp.8460-8469. 10.1039/d5qi01567g. hal-05304185

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ARTICLE

# Diversity of supramolecular assemblies based on photoactive Cu(I) trimetallic building blocks and N donor ditopic ligands: from 1D coordination polymers to metallacycles

Received 00th January 20xx,
Accepted 00th January 20xx

DOI: 10.1039/x0xx00000x

Adrien Schlachter,ª Jaison Casas,ᵇ Vincent Dorcet,ª Guillaume Calvez,ª Sylvie Ferlayᵇ* and Christophe Lescopª*

A series of polymetallic Cu(I) assemblies C₁-₄ was selectively obtained by self-assembly of a preorganized trimetallic precursor B with 3,3'-bipyridine ligand L₁ and structurally related longer ligands L₂-₄, respectively, allowing to investigate the impact of ligands' backbones on architectures on the derivatives C₁-₄. While linkers L₁ and L₂ led to the formation of 1D coordination polymers (C₁,₂), the newly prepared alloxazine-functionalized ligands L₃ and L₄, promoting the appearance of steric constraints and π-π interactions, led to the formation of discrete hexametallacycles (C₃,₄). Structural characterization via X-ray diffraction confirmed the role of ligand design in determining the final architectures. The solid-state photophysical properties of ligands L₃ and L₄, trimetallic precursor B and derivatives C₁-₄, are reported. L₃ and L₄ exhibit weak yellow fluorescence at room temperature (RT), while the trimetallic precursor B displays intense yellow ³MLCT phosphorescence at RT. Assemblies C₁-₄ show varied photophysical behaviors including ³MLCT phosphorescence for C₁, ligand centered phosphorescence and fluorescence for C₂ and C₄, respectively, while C₃ is non-emissive. This study provides new insights into the steric and electronic factors governing Cu(I)-based luminescent materials' preparation, highlighting diverse photophysical behaviors including efficient RT emission performances.

## Introduction

An innovative alternative to traditional synthetic strategies for creating innovative molecular frameworks lies in the use of self-assembly processes, in which non-covalent kinetically labile bond formations drive the organization of individual building blocks through self-sorting and self-correction mechanisms, affording *in fine* thermodynamically stable products.¹ Over the past decade the use of the metal-ligand coordination bonds has led to the formation of a large number of multimetallic supramolecular structures, in particular accordingly to Coordination Driven Supramolecular (CDS) chemistry synthetic principles.²,³ The CDS chemistry employs pre-designed coordination complexes characterized by well-defined geometries (being in most cases hardly accessible from single metal center coordination sphere) and vacant coordination sites. These pre-organized precursors are subsequently combined by connecting polytopic ligands to yield multimetallic assemblies whose sizes and geometries are precisely determined by the symmetrical arrangement of the linking sites

within the individual building blocks. This strategy has enabled the development of a large diversity of multifunctional assemblies, including extended coordination networks and discrete metallacages, bearing for example remarkable ability for selective encapsulation of specific guest species and/or original reactivity within their internal confined spaces.³ Among these intricate polymetallic CDS structures, metallo-macrocycles frequently appear as the targeted scaffolds or as sub-units within more complex molecular architectures.

So far, the use of Pt(II) and Pd(II) metal centers dominates CDS chemistry since these ions offer strong preferences for a rigid square-planar coordination geometry, along with highly directional, thermodynamically stable, yet kinetically labile metal-ligand interactions. This combination of properties ensures successful CDS synthetic processes²,³ and has been historically key to the growth of this field. However, alternatives to these leading trends have appeared in the recent years,⁴ shifting towards exploring alternative metal centers and coordinating groups, broadening thus the design of crystal engineering related with CDS chemistry. In this context, we have recently introduced pre-assembled Cu(I)-based precursors,⁵ such as the [Cu₂(µ₂-dppm)₂]²⁺ bimetallic fragment A⁵f⁻¹ (Scheme 1), where dppm stands for bis(diphenylphosphino)methane), into CDS self-assembly strategies. Although Cu(I) ions typically exhibit labile, flexible, and low-directional coordination sphere, these pre-assembled Cu(I)-based precursors have proven to be effective in the selective preparation of original supramolecular assemblies.⁵f⁻⁻m Moreover, these polymetallic species exhibit a variety of

<footnote>ªDr. A. Schlachter, Dr. V. Dorcet, Dr. G. Calvez, Dr. C. Lescop
INSA Rennes, CNRS, Univ Rennes, ISCR - UMR6226, F-35000 Rennes, France
E-mail: christophe.lescop@insa-rennes.fr.</footnote>

<footnote>ᵇDr. J. Casas, Dr. S. Ferlay
CNRS, CMC UMR 7140, Université de Strasbourg, Strasbourg 67081 Cedex, France
E-mail: ferlay@unistra.fr.</footnote>

<footnote>Electronic Supplementary Information (ESI) available: experimental, analytical and crystallographic details. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/x0xx00000x</footnote>
luminescence properties due to the versatile photophysical behaviours associated with Cu(I)-based compounds,⁶ This series of results opened up appealing perspectives for designing innovative luminescent solid-state supramolecular materials. It was highlighted that, in order to successfully introduce the Cu(I) ion in CDS chemistry processes, a specific assembling ligand design is required in order to overcome the limitations due to the high flexibility of the Cu(I) coordination spheres and impose directionality at the level of the coordination links formed on the vacant sites of the metal ions on these precursors.⁵ª Therefore, a special attention has to be paid to the preparation of such pre-assembled polymetallic precursors.

<figure><img src="image_2.png" /><figcaption>**Scheme 1** Molecular structure of a) the precursors A and B; b) the linkers L₁-₄</figcaption></figure>

Within the series of polymetallic luminescent assemblies that have been previously isolated from the preassembled bimetallic precursor **A**, three RT highly luminescent tetrametallic dicationic discrete metallacycles Dₓ (X = Cl, Br, I)⁷ (scheme 2b) were prepared resulting from the reaction of **A** with the 3,3'-bipyridine ligand L₁ in presence of halide ions. In the case of the preparation of these assemblies, it was highlighted that it is necessary to introduce µ₂-X bridging halide ligands, affording the Cu(I) bimetallic sub-unit **A'** (scheme 2b), to lock the Cu(I) bimetallic fragments in a conformation that allows conducting selective CDS self-assembly processes toward the formation a metallacyclic backbone (scheme 2b). As a result, three new tetracationic metallacycles were obtained selectively, presenting enhanced solid-state luminescence properties characterized by phosphorescence radiative relaxation processes and high RT emission quantum yields (Φem = 55–80 %). Taking into consideration the structural resemblances of the bimetallic precursors **A'** and the trimetallic precursor **B** (Scheme 2), We have been motivated to explore the scope and limitation of the use of a monocationic trimetallic Cu(I) complex **B** as potential pre-assembled building block for the preparation of new polymetallic supramolecular Cu(I) assemblies embedded with solid-state luminescence properties. This precursor **B** (Scheme 1a) presents a linear array of three Cu(I) ions stabilised by two dpmp ligands (where dpmp stands for bis-diphenylphosphinomethyl)phenylphosphine) and two µ₂-bridging bromide ions. The preparation and characterization of this trimetallic complex was previously reported⁸ together with

its reactions with a series of main group element organometallic ligand '$E_n''^{2g}$ (E= P, As; n = 2,3,5) such as the '$P_5$' pentaphosphaferrocene ligand, affording either discrete derivative or 1D-coordination polymers (1D CPs).⁸ While this early work evidenced the versatility of the assembly processes that can be directed using derivative **B**, no description of its own luminescence properties was reported (while assemblies of **B** with the '$E_n$' ligand complexes are not luminescent). However, **B** reveals to be an appealing RT solid-state luminophore (*vide infra*) which potentially makes it an attractive photoactive pre-assembled building-block to conduct self-assembly reactions toward new luminescent species. Indeed, in the present study, **B** was reacted (Scheme 2a) at room temperature (RT) with four different ditopic N-donor organic linkers L₁-₄ bearing the 3-pyridyl moiety (L₁-₃) or pyrimidine moiety (L₄) as terminal coordinating group (Scheme 1b). In addition, for L₃-₄, the presence of the structuring alloxazine moiety will add recognition schemes between the components during the assembling process. This allowed us to build new coordination compounds C₁-₄ (Scheme 2a) presenting various emission properties, and demonstrated the powerful approach of the crystal engineering for the control of the formation of species presenting different dimensionalities. Four new polymetallic supramolecular assemblies C₁-₄ have been obtained (Scheme 2a), displaying either infinite one-dimensional coordination polymers (C₁,₂) or discrete metallacyclic (C₃,₄) scaffolds. Their syntheses, characterizations, X-ray single crystal molecular structures, solid-state luminescence properties are reported below.

<figure><img src="image_3.png" /><figcaption>**Scheme 2** Preparation and schematic structures of the derivatives a) C₁-₄, b) Dₓ⁸ from bimetallic **A'** and trimetallic **B** Cu(I) complexes.</figcaption></figure>

## Results and discussion

### 1. Syntheses of ligands L₃-₄

Regarding the results obtained in the course of this study in a first step using the 'simple' linkers L₁ and L₂ (*vide infra*), our attention was directed toward the linkers L₃,₄ appended with an additional alloxazine unit as lateral functional and structuring π-conjugated group. L₃ presents similar metrics as L₂. The alloxazine moiety (Scheme 1b) is an isomer of the isoalloxazine, related to flavins and belongs to an important class of
biomolecules exhibiting three different redox and protonation states including an intermediate radical state.⁹ They have been known to perform chelation of various metal ions through 4-O

<figure><img src="image_4.png" /><figcaption>**Scheme 3** Synthetic pathway for the preparation of L₃ and L₄</figcaption></figure>

and 5-N site of the alloxazine core affording complexes of alloxazine coordinated through the O,N alloxazine core with transition metals have been reported mostly with 4d and 5d metals such as ruthenium, rhenium, iridium and tungsten.⁹ Finally, combining the alloxazine core and bipyridyl moieties can lead to interesting enhanced π-stacking within metallo-organic frameworks as already observed with the parent ligand presenting N donor atom in position 4 of the pyridyl ring, where only the N donor atoms on the pyridine are involved in coordination to metal ions, preventing the coordination abilities of the alloxazine core. This parent ligand has been already reported for the preparation of extended coordination polymers.¹⁰

L₃ and L₄ have been obtained following the synthetic pathway represented in scheme 3 (see experimental section), in 53 % and 25 % yields respectively, starting from the condensation of alloxane with 3,6-dibromobenzo-1,2-diamine¹⁰ in the presence of boric acid, followed by a methylation using methyl iodide; then a Suzuki–Miyaura cross-coupling was carried out with 3-pyridyl-1-boronic acid (or 3,5-pyrimidine-1-boronic acid), leading to L₃ and L₄ respectively.¹⁰

## 2. Preparation of the derivatives C₁-₄.

The trimetallic precursor B was prepared in-situ. In the case of the preparation of the species C₁-₂, CH₂Cl₂ solutions of one equivalent of [Cu(CH₃)CN]₄PF₆, two equivalents of CuBr and two equivalents of dpmp ligand were prepared (Scheme 1a) and left upon stirring at room temperature (RT) under air for one hour, affording colorless solutions. Then solutions of one equivalent of the ligands L₁₂ dissolved in CH₂Cl₂ were added, leading to colorless clear solution. These solutions were left upon stirring at RT for one night. The crude solutions obtained were then left to crystallize under air at RT upon pentane vapor diffusions. After one-week, homogeneous batches of well-shaped single crystals of derivatives C₁₂ were obtained.¹¹ In the case of the preparation of the species C₃-₄, the trimetallic precursor B was prepared similarly using ligands L₁₂ and CHCl₃ as solvent, affording colorless solutions. On the top of these solutions were layered of CH₂Cl₂ solutions of equivalent of the ligands L₃₄ affording after two weeks of slow diffusions homogeneous batches of block-shaped single crystals of derivatives C₃-₄.¹¹ After filtration, these samples were dried affording homogeneous colorless (C₁-₂), yellow (C₃) or orange (C₄) polycrystalline solids of the derivatives C₁-₄ with good yields of 70-85 %.

<figure><img src="image_5.png" /><figcaption>**Fig. 1** Views of the molecular X-ray structures of the 1D CPs a) C₁ and b) C₂: top, fragments showing the local coordination of two linkers on a central trimetallic building block; middle, general view of the 1D CPs scaffolds, bottom, general views of the molecular stacking in the crystals (top and middle views: counter-anions and solvent molecules have been omitted for clarity, bottom: stick and ball views with Cu₃Br₂ units highlighted as blue polyhedrons and the connecting ligands highlighted as black rectangles).</figcaption></figure>

These derivatives are characterized in their solid-state IR spectrum by a superposition of the bands typical of the dpmp ligands and of the different ditopic L₁₄ connecting ligands used, together with an intense band at ca 830 cm⁻¹ typical of the PF₆ counter-anion, supporting the presence in all samples prepared of both dppm and the connecting ligands used in cationic assemblies. X-ray single crystal diffraction analyses¹¹ of derivatives C₁-₄ were conducted on single crystals obtained along the synthetic procedures applied.

## 3. Structural Characterization of the 1D-CPs C₁,₂.

Single crystal diffraction analyses (see crystallographic data in table S1)¹¹ revealed in the case of C₁ the formation of a 1D CP (Fig. 1a) with an asymmetric unit containing two symmetrically independent but chemically similar [Cu₃(µ-Br)₂(dpmp)₂]L₁(PF₆)] moieties and 3.5 included CH₂Cl₂ solvent molecules. Waved chains are then formed due to the interconnection of the components via bond formation between the N donor atoms of the linear L₁ ligand and the two external Cu(I) ions of [CuI₃(µ-Br)₂(dpmp)₂]⁻ building block B (Scheme 2). These external Cu(I) metal centers of the trimetallic building blocks exhibit therefore a distorted tetrahedral P₂Br₁N₁ coordination sphere while the internal Cu(I) metal centers' keep a distorted tetrahedral P₂Br₂ coordination sphere as observed in B). The intermetallic distance significantly increased (from 2.8470(1) - 2.8995(1) Å in B to 3.260(7) - 3.402(13) Å in C₁, Table S2), implying that there are no cuprophilic interactions¹² in C₁. Such an increase of the intermetallic distance was also previously observed as B was associated with organometallic P₃ and P₅ ligand-complexes within 1D CP networks.⁷ The coordination of the N-donors atoms induces moreover an increase of the Cu-Br distance and the Cu-Br-Cu angles (Table S2) in C₁ compared to what is
observed for **B**, which is directly related to the increase of the coordination number of the external Cu(I) ions of the trimetallic units. Conversely, the Cu-P distances (Table S2) are mostly unchanged comparing **B** and **C**₁. In addition, the coordination of the N donors atoms of **L**₁ is transoid (Fig. 1a) considering the ligands' backbone symmetry. These informations are in contrast with what is observed in the case of the structure of the metallacycles **D**ₓ⁸ (Scheme 2b) in which the N donor atoms of **L**₁ are cis-orientated, leading to the ring structure of **D**ₓ. Hence, changing the pre-assembled Cu(I) units reacted with **L**₁ from the bimetallic building-block **A**' to the trimetallic building-block **B** induces a strong alteration of the polymetallic molecular scaffolds, from discrete metallacycle in **D**ₓ to 1D infinite chain in **C**₁. However, the metric data (Table S2) such as the N-Cu distances are comparable within **D**Br (d(Cu-N) = 2.109(4) Å and 2.121(5) Å)⁸ and **C**₁ (d(Cu-N) = 2.098(7) - 2.107(7) Å, Table S2) as well as the Cu-Cu-N angles (DBr: 150.76(5), and 150.27(6) °; C₁: 146.7 °). Within the 1D CP polymer backbone of **C**₁, the torsion angle between the two six-membered rings of the coordinated ligands **L**₁ are 0.8° and 26.1°, which is in the same range of the torsion angle observed in DBr (17.2°).⁸ These data suggest that no specific steric constrains occur within the scaffold of **C**₁ at the connecting ligands' environment. Thus, the observed discrepancy must be related with the larger dimensions of **B** compared to the one of **A**.

X-ray crystal structure determination (Table S1) revealed that the derivative **C**₂ built from the longer linker **L**₂ presents also a 1D CP scaffold than **C**₁ (Fig. 1b), bearing waved chains in which the repetition unit's is composed by one [Cu₃(µ-Br)₂(dpmp)₂]L₂(PF₆)·3 CH₂Cl₂ fragment. Metric data are mostly comparable with those observed for **C**₁ (Table S1). The connecting ligands **L**₂ present also a transoid type of coordination (Fig. 1b) and their backbone is not fully planar with torsion angles of 24.7° and 28.8° between the central phenyl ring and the terminal 3-pyridyl rings.

Finally, regarding the crystal packing, both 1D CPs **C**₁ and **C**₂ present similar extended organization in the crystal with all polymeric chains being parallel (Fig. 1), separated by included anions and solvent molecules and presenting only weak non-specific short contact interchain interactions.

Considering the discrepancy observed between the metallacycle scaffolds of the **D**ₓ series (obtained from **A**) and the 1D-CPs of the derivatives **C**₁,₂ (obtained from **B**), we have aimed exploring further the parameters that can drive the selection of one of these architectures over the other one. In the case of **D**Br, it was suggested that a minimization of steric constrains between the different Cu(I) precursors connected by the 'shorter' linker **L**₁ might be a parameter to promote the formation of the metallacycle backbone toward the 1D CP framework, due to a 'sterical protection effect' that was previously suggested to explain the formation of related Cu(I) tetrametallic metallacycles.¹³ Using a longer Cu(I) pre-organized precursor such as **B** may allow a sufficient alteration of these constraints to promote the formation of the 1D CP scaffold. In addition, as the longer ditopic linker **L**₂ is reacted, 1D-CP scaffold is also obtained which supports the hypothesis of sterical effects between the different building-blocks to select nature of

the architectures obtained. Therefore, altering the molecular structure of the ditopic linkers reacted with **B** may also impact the nature of the scaffold of the resulting multimetallic assemblies.

### 4. Structural Characterization of the metallacycles C₃,₄.

We have targeted the ditopic linkers **L**₃ and **L**₄ (Scheme 1) in which the alloxazine groups provide a lateral unsymmetrical crowding very likely favouring cisoid-type of coordination, together with potential formation of intermolecular π-π interactions.

X-ray diffraction studies (Table S1)¹¹ performed at low temperature (LT) on single crystals of derivatives **C**₃ and **C**₄ bearing the alloxazine containing ligands **L**₃ and **L**₄ (Scheme 1) revealed different molecular scaffold compared to the 1D CP networks highlighted for **C**₁ and **C**₂.

<figure><img src="image_6.png" /><figcaption>**Fig. 2.** Views of the molecular X-ray structures of the discrete dicationic metallacycles a) and b) **C**₄: top, general views of the scaffolds, *middle*, lateral views along the Cu₆ plans, *bottom*, general views of the molecular stacking in the crystals (top and middle views: counter-anions and solvent molecules have been omitted for clarity, bottom: stick and ball views with Cu₃Br₂ units highlighted as blue polyhedrons and the connecting ligands highlighted as black rectangles).</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>**Fig. 3.** Views of the π-π interactions highlighted with blue dotted lined ellipse taking place between two neighbouring assemblies of a) **C**₃ and b) **C**₄ (the tetrametallacycles are shown in stick and ball style with all atoms colored in white with the exception of those owing to the ligands **L**₃ and **L**₄ on which the π-π interactions are highlighted).</figcaption></figure>
Both compounds crystallize in the triclinic space group P-1 with an asymmetric unit containing half of the discrete supramolecular assemblies C₃ or C₄, one hexafluorophosphate counter-anion, the unit cell being completed with disordered CH₂Cl₂ solvent molecules. These derivatives C₃ and C₄ are similar centrosymmetric dicationic hexametallacycles (Scheme 1b, Fig. 2) resulting from the connection of two [Cu₃(dpmp)₂(µ₂-Br)]⁺ trimetallic units by, respectively, two ligands L₃ or L₄ acting as ditopic linkers. In both compounds, all the six metal ions are coplanar. The external Cu(I) metal centers of each trimetallic units present similar P₂Br₁N₁ distorted tetrahedral coordination spheres while the central Cu(I) metal center have P₂Br₂ distorted tetrahedral environment as observed in B (Scheme 1). In both assemblies, the connecting ligands L₃ and L₄ adopt a cisoïd coordination with respect to the symmetry of the ligand scaffolds with the alloxazine fragments pointing out of the center of metallacycles (angles of the mean planes of the alloxazine fragments and the plane including the six metal centers: C₃; 29.5°; C₄; 37.0°, table S2). Compared to the other Cu(I) polymetallic assemblies based on this [Cu₃(dpmp)₂(µ₂-Br)]⁺ trimetallic unit, the overall metric data remain unchanged.⁷ The intermetallic distance are larger (d(Cu-Cu) > 3.35 Å, above the limit usually proposed for cuprophilic interactions)¹² than in B, and are in the same range than the distances observed in D<sub>Br</sub>, C<sub>1</sub> and C<sub>2</sub> (Table 1). Within these metallacyclic assemblies, the µ₂-bromo ligands (separated by ca. 7.50 Å in C₃ and 7.0 Å in C₄ between each of the two trimetallic sub-units present in the metallacycle) are orientated toward the center of the metallacycle and are located slightly outward of the mean plane defined by the six Cu(I) ions (deviation to the mean plane: 0.187 Å and 0.416 Å in C₃, 0.104 Å and 0.260 Å in C₄). In D<sub>Br</sub>, the intramolecular distance between the µ₂-bromo fragments is shorter which is expected since the connecting ligands C₃ and C₄ are longer than C₁ and the µ₂-bromo units are located more outward of the plane defined by the four metal centers (deviation to the mean plane: 0.812 Å) which confirms the assumption of sterical constrains lying within the D<sub>Br</sub> metallacycle, these constrains being mostly released within C₃ and C₄ scaffolds due to the larger dimensions of the connecting ligands L₃ and L₄ compared to L₁. The coordination of the ligands L₃ or L₄ on the external metal centers centers of the trimetallic units is symmetrical (Table S2) with comparable (Cu-Cu-N) angles (146.33° and 147.38° for C₃; 147.83° and 149.52° for C₃ and) and (Cu-N) bond lengths (2.085(3) and 2.087(3) Å for C₃; 2.091(7)° and 2.100(7)° for C₄). The torsion angles between the two N-donors terminal rings of the connecting ligands L₃,₄ and their central alloxazine moieties' mean planes are also very similar in both metallacycles (39.3° and 40.5° in C₃; 39.8° and 40.5° C₄). All these metric data support the assumption of a lack of specific intramolecular sterical constrains lying between the Cu₃ sub-units and the connecting ligands L₃,₄ within the metallacycle's backbones of assemblies C₃,₄, conversely to what was observed within metallacycle D<sub>Br</sub>. Very likely, the alloxazine moieties on L₃,₄ supply a lateral crowding effect that promote the cisoïd conformation observed in the crystal structures of the derivatives C₃,₄ and favour the metalacyclic backbone formation at the expense of a 1D CP coordination network. Interestingly,

both derivatives C₃ and C₄ exhibit different crystal packings (Fig. 2, bottom) that however feature in each case intermolecular π-π interactions (intermolecular distances below 3.5 Å) involving the alloxazine moieties of two neighbouring assemblies, all alloxazine fragments being involved in such interactions (Fig. 3, these intermolecular interactions are more intense in the case of C₃ and C₄). This is in a marked contrast with the crystal packings of the derivatives D<sub>Br</sub>, C₁ and C₂ where none of such intermolecular interactions are observed. The generation of such π-π interactions specifically allowed by the presence of the alloxazine moieties in the core of the connecting ligands L₃ and L₄ might also be a factor that contributes in the stabilization of the metallacyclic structure of the assemblies C₃ and C₄ (Fig. 2).

**5. Study of the photophysical properties.**

L₃ and L₄ are yellow colored polycrystalline powders as seen under visible light and emit a weak yellowish light in the solid state at RT upon photoexcitation (λ<sub>ex</sub> = 365 nm). Thermal variations study¹¹ of the emission spectra and the decay time of the excited state of both ligands L₃ and L₄ reveal fluorescence radiative relaxation pathways characterized at RT for L₃ by a large band in its emission spectra centerer at 613 nm (λ<sub>ex</sub> = 340 nm) associated with a monoexponential decay time of 5 ns (Table S3) and for L₄ by a large band emission spectrum centered at 599 nm (λ<sub>ex</sub> = 340 nm) and biexponential decay times of 40 ns (main contribution) and 13 ns (minor contribution) (Table S4).

Absorption spectra at room temperature of derivatives B, C₁ and C₂ show a broad band in the near UV-region with its lower energy λ<sub>max(abs)</sub> centered at (λ<sub>-max(abs)</sub> at 308 nm (B), 363 nm (C₁) and 320 nm (C₂), Fig. S14-S16), typical of MLCT transitions.¹⁴ No absorption is observed in the visible region of these spectra which is in agreement with the colorless aspect of the polycrystalline powder samples obtained. Conversely, polycrystalline samples of the assemblies C₃ and C₄ are yellow (C₃) or orange (C₄) colored as seen under visible light. Accordingly, their absorption spectra display large bands whose lower energy λ<sub>max(abs)</sub> (centered at 430 nm for C₃ and 416 nm for C₄, Fig. S17, S18) are significantly red-shifted compared to the bands observed in the absorption spectra of B, C₁ and C₂.

<figure><img src="image_8.png" /><figcaption>**Fig. 4.** Thermal variation of the solid-state normalized emission spectrum of B (λ<sub>ex</sub> = 320 nm; the gap centered at 640 nm arise from a second harmonic suppression) and C₁ (λ<sub>ex</sub> = 380 nm, the signal at ca. 430 nm is an instrument artefact).</figcaption></figure>

At RT under air, polycrystalline batches of derivatives B, C₁, C₂ and C₄ display respectively an eye-perceived intense yellow (B), intense greenish (C₁), weak yellow (C₂), and weak yellow-orange (C₄) solid-state RT luminescence while C₃ is non emissive. The intensities of photoluminescence signal of derivatives B, C₁,
C₂ and C₄ increase as the sample are cooled down to ca. 80 K with a shift to a green-colored luminescence at LT in the case of the derivative **B** while no significant shift of the eye-perceived color of emitted light is observed for C₁, C₂ and C₄, solid-state sample of C₃ remaining non-emissive at LT. The excitation spectra at RT of these four photoluminescent derivatives show large excitation domains in the near UV region with one maximum at ca. 320 nm for **B** (λ<sub>ex</sub> = 500 nm), two maxima at ca. 330 nm and ca. 380 nm for C₁ (λ<sub>ex</sub> = 500 nm), one maximum at ca. 380 nm for C₂ (λ<sub>ex</sub> = 540 nm) and one maximum at ca. 325 nm for C₄ (λ<sub>ex</sub> = 500 nm). Upon excitation at 320 nm (**B**), 380 nm (C₁) and 330 nm (C₂ and C₄) at 300 K (see excitation spectra Fig. S27-S30), the emission spectra display at 300 K a broad featureless band centered at λ<sub>em</sub> = 532 and 506 nm for **B** and C₁, respectively (Fig. 4, Table 1), two maxima at 490 nm and 523 nm and a shoulder at ca. 575 nm for C₂, and a maximum at 574 nm and a shoulder at ca. 500 nm for C₄ (Fig. 5, Table 1). In addition, RT emission decay times of **B** and C₂ were treated by biexponential fits affording for **B** τ₁ and τ₂ lifetimes of 11 µs and 40 µs, and for C₂ τ₁ and τ₂ lifetimes of 0.3 µs and 1.1 µs. In contrast, RT emission decay times of C₁ and C₄ are mono-exponential (τ = 14 µs for C₁ while τ= 6 ns for C₄ being markedly shorter than the lifetimes measured for **B**, C₁ and C₃). Finally, RT emission quantum yields (EQY) reach 88 % for **B**, 60 % for C₁, and 7 % for C₂ (the RT intensity of the luminescence of the signal in the case of C₄ is too weak to allow a quantitative determination of its RT EQY (C₄'s EQY < 1 %)). To get more insights about the emission properties of derivatives **B**, C₁, C₂ and C₄, temperature dependent photophysical characterizations were conducted upon temperature cooling from 300 K to 80 K. For each derivative, a net increase of the signal intensity is observed as the temperature decreases. In the emission spectra of **B** under excitation at 320 nm, a gradual blue shift (Fig. 4) of the large band displayed at 300 K (λ<sub>max</sub> = 532 nm) takes place yielding at 80 K a large signal with λ<sub>max</sub> = 506 nm (Table 1). Regarding the thermal variation of the lifetimes of the excited state of **B**, a continual and significant increase of two RT components of the decay time is observed upon cooling (Fig. S33a), reaching τ₁ = 190 µs and τ₂ = 48 µs at 80 K (Table 1 and Table S5).

<figure><img src="image_9.png" /><figcaption>**Fig. 5.** Thermal variation of the solid-state normalized emission spectrum of C₂ (λ<sub>ex</sub> = 330 nm) and C₄ (λ<sub>ex</sub> = 330 nm).</figcaption></figure>

Considering the 1D CP **C**₁, a very slight blue shift of the large band observed at 300 K takes place (λ<sub>max</sub> = 512 nm at 80K). The decay time of the excited state remains consistent over the full emission spectrum and is monoexponential down to 250 K (Fig. S34a) with a very moderate variation of the value but transfer to biexponential at lower temperatures (at 250 K, τ₁ = 69 µs and

τ₂ = 17 µs, Table S6). Both components' values then increase as the temperature decreases reaching τ₁ = 138 µs and τ₂ = 36 µs at 80 K (Table 1 and Table S6). Upon cooling, the profile of the emission spectrum of the 1D-CP **C**₂ is mostly unchanged but gets more structured. However, the higher energy maximum peak at 300 K displays a slight blue shift upon cooling (527 nm at 80 K). The decay time of the excited state remains biexponential (Fig. S35a) and the values continuously increase with the cooling (τ₁ = 49 µs and τ₂ = 23 µs at 80 K, Table S7). Finally, concerning the emission spectra of the metallacycle **C**₄, a structuration of the profile of the spectrum observed at 300 K takes place upon cooling with an enhancement of the intensity of the signal at 500 nm (observed as a shoulder at 300 K) compared to the maxima observed at 574 nm at 300 K (this signal being slightly blue shifted as the temperature decreases, reaching 560 nm at 80 K). In addition, shoulders at ca. 470 nm and ca. 615 nm appear in the lowest temperatures spectra. Concomitantly, the thermal variation of the decay times measured for **C**₄ increases (Fig. S36a) continually as the temperature decreases and reaches 12 ns at 80 K (Table S8).

Hence, the solid-state photophysical properties of the reported coordination compounds exhibit quite a wide range of behaviours, suggesting diverse mechanisms of relaxation processes after UV-vis light excitation. On the one hand, derivatives **B**, **C**₁ and **C**₂ present remarkable (B and C₁) or moderate (C₂) RT EQY associated with microseconds time range decay time of the excited states. The VT emission behavior of phases **B** and **C**₁, along with the thermal variations of their luminescence decay times (Table 1), suggests that the emission properties of these compounds are governed by a triplet metal-to-ligand charge transfer phosphorescence process. For discrete derivative **B**, a pronounced rigidochromic effect is observed that likely accounts for the observed blue shift in its emission spectrum upon cooling. At low temperatures, an increased rigidity of the molecular backbone in this discrete trimetallic Cu(I) complex restricts structural relaxation in the excited state and suppresses distortion associated with cuprophilic interactions, thereby stabilizing higher-energy emissive states. Such behavior has been previously reported for Cu₄I₄-based luminescent derivatives.¹⁵ In contrast, this effect is not observed for the 1D coordination polymer **C**₁, in which cuprophilic interactions are absent. Furthermore, the formation of an extended coordination network in **C**₁ likely imposes greater intrinsic rigidity at RT compared to the discrete structure of **B**, thus minimizing the impact of temperature-induced rigidity changes on the excited-state dynamics.
<table><caption>**Table 1.** Photophysical data in the solid-state for the derivatives L₃, L₄, B, C₁, C₂ and C₄ ($k_r = Φ_{em}/τ_{obs}$; $k_{nr} = (1-Φ_{em})/τ_{obs}$; $k_r$ and $k_{nr}$ have been calculated based on the longer and main component of the decay time), a = shoulder; (M) indicates the major component and (m) indicates the minor component extracted when biexponential decays times are determined.</caption><thead><tr><th></th><th>T<br>(K)</th><th>λ<sub>max</sub><br>(nm)</th><th>FWHM<br>(cm<sup>-1</sup>)</th><th>Φ<sub>em</sub><br>(%)</th><th>τ<sub>obs</sub></th><th>k<sub>r</sub><br>(s<sup>-1</sup>)<sup>a</sup></th><th>k<sub>nr</sub><br>(s<sup>-1</sup>)<sup>b</sup></th></tr></thead><tbody><tr><td rowspan="2">L<sub>3</sub></td><td>80</td><td>613</td><td>1400</td><td>-</td><td>11 ns</td><td>-</td><td>-</td></tr><tr><td>300</td><td>613</td><td>1350</td><td>-</td><td>5 ns</td><td>-</td><td>-</td></tr><tr><td rowspan="2">L<sub>4</sub></td><td>80</td><td>598</td><td>3860</td><td>-</td><td>189 ns (M)<br>48 (m)</td><td>-</td><td>-</td></tr><tr><td>300</td><td>599</td><td>3800</td><td>-</td><td>40 ns (M)<br>13 ns (m)</td><td>-</td><td>-</td></tr><tr><td rowspan="3">B</td><td>80</td><td>506</td><td>2900</td><td>-</td><td>190 μs (M)<br>48 μs (m)</td><td>-</td><td>-</td></tr><tr><td>300</td><td>532</td><td>4000</td><td>88</td><td>40 μs (M)<br>11 μs (m)</td><td>2.2×10<sup>4</sup></td><td>3.0×10<sup>3</sup></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td rowspan="2">C<sub>1</sub></td><td>80</td><td>512</td><td>4090</td><td>-</td><td>138 μs (M)<br>36 μs (M)</td><td>-</td><td>-</td></tr><tr><td>300</td><td>506</td><td>4340</td><td>60</td><td>14 μs</td><td>4.3×10<sup>4</sup></td><td>2.9×10<sup>-2</sup></td></tr><tr><td rowspan="3">C<sub>2</sub></td><td>80</td><td>527</td><td>3370</td><td>-</td><td>49 μs (M)<br>23 μs (m)</td><td>-</td><td>-</td></tr><tr><td>300</td><td>523</td><td>3490</td><td>7</td><td>1.1 μs (m)<br>0.3 μs (M)</td><td>6.4×10<sup>4</sup></td><td>8.5×10<sup>-1</sup></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td rowspan="2">C<sub>4</sub></td><td>80</td><td>500<sup>a</sup></td><td>560</td><td>5630</td><td>12 ns</td><td>-</td><td>-</td></tr><tr><td>300</td><td>574</td><td>3670</td><td>-</td><td>6 ns</td><td>-</td><td>-</td></tr></tbody></table>

For derivative C₂, the emission lifetimes and the low RT EQY are consistent with a triplet-state origin of the luminescence. The thermal evolution of the emission spectra, along with the presence of vibrational substructures in particular at low temperature, suggests that the emission may arise from a metal-perturbed triplet intraligand charge transfer (³ILCT) or triplet ligand-to-ligand charge transfer (³LL'CT) state, where L = L₂ and L' = dpmp. In contrast in the case of derivative C₄, the emission lifetimes and the very low RT EQY instead point toward a fluorescence-type radiative relaxation process. This emission is likely centered on the coordinated ligand L₄ and involve a metal-perturbed singlet ILCT (¹ILCT) or LL'CT (¹LL'CT) transition, where L = L₄ and L' = dpmp. This assignment is further supported by the close similarity in λₘₐₓ values of the RT emission spectra of free ligand L₄ and the metallacycle C₄. It is not straightforward to rationalize from these measurements the differences observed between the photophysical processes taking place in the 1D-CP C₂ and the metallacycle C₄. These species differ from both their supramolecular organisation and the nature of the π-conjugated core of the N-donor organic linker coordinated to the Cu(I) trimetallic sub-units and it is very likely that multiple factors contribute to their distinct luminescence properties. Notably, the presence of the extended π-conjugated alloxazine fragments in the ligand L₄ in C₄ likely plays a dominant role by significantly lowering the energy levels of the ligand's frontier molecular orbitals. This can shift the distribution of electronic density within the excited states of the assembly toward the connecting ligand framework, thereby reducing the

participation of the Cu(I) building-blocks' orbitals in the emission process. As a result, the emission properties in C₄ may be predominantly ligand L₄-centered fluorescence, with only a very minor contribution from the metal-based orbitals. In contrast in the case of the 1D-CP C₂ based on the ligand L₂ featuring a less extended π-conjugated backbone (as indicated by higher energy λₘₐₓ(abs) values) an intermediate situation may arise with a larger involvement of the Cu(I) building blocks (through the contribution of their spin-orbit coupling values in particular) that may promote efficient radiative transitions from the lowest-lying triplet state. It is worth noting that a similar dependence of the photophysical process of a series of 1D-CPs derived from a tetrametallic pre-assembled precursor with the extend of the π-conjugation of the internal core of the N-donors connecting ligands has been recently described and rationalized.⁵⁾

## Conclusions

The ability of trimetallic pre-assembled precursor B to react with ditopic linkers selectively allowing the formation of polymetallic assemblies is demonstrated though this study. The crucial role of both precursor architecture and linker design in directing the self-assembly of these polymetallic Cu(I) assemblies is highlighted. Indeed, in contrast with the previously studied bimetallic precursor A' that enabled the formation of discrete tetrametallic metallacycles Dₓ from its reaction with the 'simple' ditopic linkers L₁,₂, the trimetallic precursor B led to the synthesis of 1D CPs C₁,₂ when associated with these linkers. However, introducing the alloxazine-functionalized linkers (L₃,₄) resulted in a shift back to discrete hexametalacycles (C₃,₄), demonstrating that lateral steric hindrance and π-π interactions can be harnessed to control supramolecular organization. The solid-state photophysical properties of the derivatives studied exhibit diverse relaxation mechanisms upon UV-visible light excitation. Derivatives B and C₁ demonstrate good RT EQY and microsecond-range decay times, indicative of triplet metal-to-ligand charge transfer phosphorescence process. In contrast, regarding the 1D-Cp C₂ that displays a weak RT EQY and shorter emission lifetimes, metal-perturbed triplet intraligand charge transfer (³ILCT) or triplet ligand-to-ligand charge transfer (³LL'CT) state can account for the luminescence properties observed. Finally, C₄ exhibits fluorescence-based radiative relaxation, likely due to metal-perturbed ligand centered intraligand charge transfer (¹ILCT). All in all, these results provide valuable insights for the rational design of luminescent Cu(I)-based metallosupramolecular assemblies with tailored architectures.

## Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

## Conflicts of interest
There are no conflicts to declare.

## Data availability

Crystallographic data have been deposited at the CCDC under 2441072 (C₁), 2441073 (C₂), 2441074 (C₃) and 2441075 (C₄), and can be obtained from https://www.ccdc.cam.ac.uk/structures/.

## Acknowledgements

This work was supported by the CNRS, the ANR (ANR PRC SMAC and ANR PRCI SUPRALUM), the French ‘Ministère de l’Enseignement Supérieur, de la Recherche et de l’Innovation’ and the French ‘Ministère des Affaires Etrangères’. C.L. thanks the Alexander von Humboldt Foundation for a fellowship for experienced researcher. Financial support from the University of Strasbourg Agence Nationale de la Recherche (ANR) through BattAllox project ANR-20-CE05-0005 are acknowledged.

## Notes and references

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For experimental details and characterization, detailed photophysical and crystallographic data, see ESI.

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