Dual-Emissive Rectangular Supramolecular Pt(II)-p-Biphenyl with 4,4′-Bipyridine Derivative Metallacycles: Stepwise Synthesis and Photophysical Properties

Mixed-ligand tetranuclear supramolecular coordination complexes (SCCs) of Pt(II)-p-biphenyl and bridging ligands derivatives of 4,4′-bypiridine (8)–(10), were synthesized and characterized. The SCCs were synthesized stepwise, starting from the Pt-p-biphenyl -Pt core. The crystal structure of complex {[Pt(2,2′-bpy)]4(μ-bph)2(μ-(4,4′-bpy)2}{PF6}4 (2,2′-bpy = 2,2′-bipyridine, bph = p-biphenyl and 4,4′-bpy = 4,4′ bipyridine), was determined using single-crystal diffraction methods. The emission profile of the tetranuclear complexes (8)–(10) was influenced by the length of the bridging ligands and was found to depend on solvent polarity. Dual-emission patterns in methanol–water mixtures were observed only in the cases of complexes (9) and (10), attributed to aggregation-induced emission phenomena.


Introduction
The adjustment of the optical characteristics of transition metal complexes by means of a systematic modification of both their structure and ligands constitutes a significant undertaking within the realm of synthetic inorganic chemistry.Without a doubt, it certainly contributes to the improvement of technological applications, including solar cells [1,2], light-emitting diodes [3,4], nonlinear optical materials (NLO) [5,6], agents for bioimaging and biosensing [7,8], etc., alongside facilitating the systematic investigation of their structure-activity relationship.In recent decades, there has been remarkable research interest regarding the investigation of the optical properties displayed by supramolecular coordination complexes (SCCs), such as 2D-metallacycles and 3D-metallacages.This increased interest can be attributed to their ability to modulate their size, shape, and charge through the coordinated ligands [9].
The efficient construction of SCCs can be achieved through either spontaneous coordination-driven self-assembly or through a planned stepwise synthesis.Platinum and palladium molecular squares constitute a significant category of 2D metallacycles, wherein four metal atoms occupy the vertices of a square and are bridged by four bridging ligands.The coordination sphere of each metal is completed by two atoms of ancillary ligand(s) (Figure 1).
Apart from the rectangular squares, there is another category of supramolecular complexes referred to as rhomboidals.While the angles in the squares are approximately 90°, in rhomboidals, the angles are estimated to be greater due to the trans-orientation of bridging ligands [36,37].Rhomboidal Pt(II) complexes have been reported, starting from 2,9-bis[trans-Pt(PEt3)2NO3]phenanthrene and the equivalent addition of a non-linear ligand.These complexes exhibited excellent photophysical properties [37], leading to their Apart from the rectangular squares, there is another category of supramolecular complexes referred to as rhomboidals.While the angles in the squares are approximately 90 • , in rhomboidals, the angles are estimated to be greater due to the transorientation of bridging ligands [36,37].Rhomboidal Pt(II) complexes have been reported, starting from 2,9-bis[trans-Pt(PEt 3 ) 2 NO 3 ]phenanthrene and the equivalent addition of a non-linear ligand.These complexes exhibited excellent photophysical properties [37], leading to their potential use in cancer cell imaging and cancer chemotherapy.In vivo experiments have shown low toxicity in healthy cells [38].Pollock et al. [39] reported on multinuclear bis(phosphine)Pt(II) metal complexes in self-assembled coordination cages due to their favorable photophysical properties, including tunability and long-lived excited states.The focus was on the development of highly emissive rhomboidal structures using anilinecontaining donors and Pt-based metal acceptors.The authors successfully synthesized a series of rhomboidal complexes with tunable emission wavelengths across the visible spectrum by varying the functional groups attached to the aniline core.
While there is extensive literature on the synthesis of various platinum tetranuclear molecular squares with equal in length BLs, the exploration of rectangular structures with different length BLs is relatively rare [21,27].However, recently Chen et al. [40] reported a series of SCCs with ligands, modified 4,4-bipyridine and p-phthalic acid in order to investigate their photophysical properties.The introduction of platinum atoms led to a red-shift in both the absorption and emission spectra when compared to the spectra of the free ligands.Achieving such structures typically involves a stepwise synthesis approach, which we have employed in constructing of the rectangular structures described in this study.More particularly, we synthesized and characterized a series of platinum rectangular metallocycles based on the bimetallic complex [Pt(bpy)Cl] 2 (µ-bph), (A), incorporating the 4,4 -bpy-like ligands 4,4 -bipyridine, (B), 1,4-di(pyridin-4-yl)benzene, (C), and 4,4di(pyridin-4-yl)-1,1 -biphenyl, (D), each with increased lengths (Figure 2).To promote the aggregation of SCCs, we introduced 2,2 -bipyridine as auxiliary ligand, taking advantage of its ability to facilitate intermolecular stacking between the platinum molecular squares.The optical characteristics of these complexes were investigated, particularly in relation to the solvent polarity and their aggregation degree [41].
a series of SCCs with ligands, modified 4,4-bipyridine and p-phthalic acid in order to investigate their photophysical properties.The introduction of platinum atoms led to a redshift in both the absorption and emission spectra when compared to the spectra of the free ligands.Achieving such structures typically involves a stepwise synthesis approach, which we have employed in constructing of the rectangular structures described in this study.More particularly, we synthesized and characterized a series of platinum rectangular metallocycles based on the bimetallic complex [Pt(bpy)Cl]2(µ-bph), (A), incorporating the 4,4′-bpy-like ligands 4,4′-bipyridine, (B), 1,4-di(pyridin-4-yl)benzene, (C), and 4,4′di(pyridin-4-yl)-1,1′-biphenyl, (D), each with increased lengths (Figure 2).To promote the aggregation of SCCs, we introduced 2,2′-bipyridine as auxiliary ligand, taking advantage of its ability to facilitate intermolecular stacking between the platinum molecular squares.The optical characteristics of these complexes were investigated, particularly in relation to the solvent polarity and their aggregation degree [41].

Synthesis and Characterization
Initially, the binuclear complex [Pt(η 2 -COD)Cl]2(µ-bph) (1) was synthesized through a slight modification of the method published by Yamago group [23].The synthesis follows a three-step process as presented in Scheme 1.In the first step, a bromine-lithium exchange takes place at −78 °C in dry THF without isolating the reaction product.Then, a transmetallation reaction occurs between the 4,4′-lithiated-1,1′-biphenyl and (CH3)3SnCl, resulting in the formation of the arylstannane 4,4′-bis(trimethylstannyl)-1,1′-biphenyl in a good yield.Finally, a similar transmetallation reaction occurs between the arylstannane and the platinum complex Pt(η 2 -COD)Cl2, leading to the formation of the binuclear complex (1), which serves as the starting material for the subsequent reactions.The η 2coordinated ligand 1,5-cyclooctadiene (COD) in (1) was replaced by the chelating ligand 2,2′-bpy, in CH2Cl2, resulting in a nearly quantitative yield of the complex [Pt(bpy)Cl]2(µbph) (2).The addition of 2,2′-bpy to (2) caused a noticeable color change in the reaction mixture from colorless to bright yellow.

Synthesis and Characterization
Initially, the binuclear complex [Pt(η 2 -COD)Cl] 2 (µ-bph) (1) was synthesized through a slight modification of the method published by Yamago group [23].The synthesis follows a three-step process as presented in Scheme 1.In the first step, a bromine-lithium exchange takes place at −78 • C in dry THF without isolating the reaction product.Then, a transmetallation reaction occurs between the 4,4 -lithiated-1,1 -biphenyl and (CH 3 ) 3 SnCl, resulting in the formation of the arylstannane 4,4 -bis(trimethylstannyl)-1,1 -biphenyl in a good yield.Finally, a similar transmetallation reaction occurs between the arylstannane and the platinum complex Pt(η 2 -COD)Cl 2 , leading to the formation of the binuclear complex (1), which serves as the starting material for the subsequent reactions.The η 2 -coordinated ligand 1,5-cyclooctadiene (COD) in (1) was replaced by the chelating ligand 2,2 -bpy, in CH 2 Cl 2 , resulting in a nearly quantitative yield of the complex [Pt(bpy)Cl] 2 (µ-bph) (2).The addition of 2,2 -bpy to (2) caused a noticeable color change in the reaction mixture from colorless to bright yellow.
In the 1 H NMR spectrum of (2) in CD 2 Cl 2 , the half proton signals of the molecule were observed, reflecting its high symmetry.However, the two pyridine rings of 2,2 -bpy exhibit chemical nonequivalence, which can be attributed to a vertical orientation of bph ring system with respect to the plane of the 2,2 -bpy.This arrangement affects the chemical environment of the one pyridine ring of 2,2 -bpy that is positioned above the bph ring system, resulting in significant upfield shifts for its protons.Additionally, the proximity between the H6 of the other pyridine ring and the coordinated chlorine can result in interactions that further shift the H6 signal downfield.(Figure 3a).Additional evidence is present in the HR-ESI-MS of (2), where a cluster peak exists at m/z = 967.1224,assignable to the cation [C 34 H 31 N 4 ClSO 195 Pt 2 ] + (calc.m/z = 967.1224)which may formulated as {[Pt 2 (2,2bpy) 2 (DMSO)Cl](µ-bph)} + .The presence of the DMSO in the cation can be attributed to the addition of 5 µL DMSO to the sample in order to facilitate the solubility of (2).However, it seems that only partial replacement of the chloride takes place, as was also observed in the 1 H NMR spectrum of (2) when it dissolved in dmso-d 6 (Figure 3b).Thus, the symmetry of compound (2) was reduced, resulting in the appearance of two distinct sets of proton signals, one for each pyridine moiety of 2,2 -bpy.Under these circumstances, the H6 of 2,2 -bpy interacts with two different ligands: the coordinated chlorine located at one site of (2), which causes a downfield shift at 9.38 ppm, and the oxygen atom of the DMSO situated at the other site of (2), leading to a downfield shift at 9.66 ppm.This observation implies a stronger interaction between H6 and DMSO compared to that of chlorine (Figure 3a).The syn-conformation of the two chlorines in complex (2), which promotes the formation of the tetranuclear squares, has been observed in similar complexes as well [42].
Molecules 2023, 28, x FOR PEER REVIEW 4 of 19 Scheme 1. Reaction and conditions for the formation of complex (2).
In the 1 H NMR spectrum of (2) in CD2Cl2, the half proton signals of the molecule were observed, reflecting its high symmetry.However, the two pyridine rings of 2,2′-bpy exhibit chemical nonequivalence, which can be a ributed to a vertical orientation of bph ring system with respect to the plane of the 2,2′-bpy.This arrangement affects the chemical environment of the one pyridine ring of 2,2′-bpy that is positioned above the bph ring system, resulting in significant upfield shifts for its protons.Additionally, the proximity between the H6 of the other pyridine ring and the coordinated chlorine can result in interactions that further shift the H6 signal downfield.(Figure 3a).Additional evidence is present in the HR-ESI-MS of ( 2), where a cluster peak exists at m/z = 967.1224,assignable to the cation [C34H31N4ClSO 195 Pt2] + (calc.m/z = 967.1224)which may formulated as {[Pt2(2,2′-bpy)2(DMSO)Cl](µ-bph)} + .The presence of the DMSO in the cation can be attributed to the addition of 5 µL DMSO to the sample in order to facilitate the solubility of (2).However, it seems that only partial replacement of the chloride takes place, as was also observed in the 1 H NMR spectrum of (2) when it dissolved in dmso-d6 (Figure 3b).Thus, the symmetry of compound (2) was reduced, resulting in the appearance of two distinct sets of proton signals, one for each pyridine moiety of 2,2′-bpy.Under these circumstances, the H6 of 2,2′-bpy interacts with two different ligands: the coordinated chlorine located at one site of ( 2), which causes a downfield shift at 9.38 ppm, and the oxygen Scheme 1. Reaction and conditions for the formation of complex (2).
Attempts to react directly complex (2) with pyridinic ligands were unsuccessful due to its extremely low solubility in many organic solvents.Thus, the replacement of chlorines was achieved by adding an equimolar amount of AgNO 3 in MeCN and subjecting the mixture to sonication using a 750 W sonicator.The 1 HNMR spectrum of {[Pt(2,2bpy)(MeCN)] 2 (µ-bph)}(NO 3 ) 2 in DMSO-d 6 indicates that the pyridine rings of 2,2 -bpy remain nonequivalent due to the vertical orientation of bph ring system towards the plane of the 2,2 -bpy.Furthermore, the replacement of the coordinated MeCN by DMSO-d 6 influences the chemical shift of 2,2 -bpyH6, which is observed at 9.66 ppm.This finding supports the hypothesis of a mixed Cl-DMSO adduct when ( 2) is dissolved in DMSO-d 6 .
The formation of the SCCs ( 8)-(10) was further confirmed through high-resolution ESI-MS analysis.In all spectra, three cluster peaks were observed, assignable to the multicharged cations generated after the successive release of the [PF6] − from the original complex.Therefore, the following cations were assigned: {M-4[PF6]} 4+ , {M-3[PF6]} 3+ and {M-3[PF6]} 2+ , with the {M-4[PF6]} 4+ being the most abundant among them.The isotopic pa erns of these cations were found to match the simulated theoretical ones, as illustrated in Figure 5.
A common characteristic of the two coordination sites is the twisted orientation of the 4,4 -bpy and bph rings with respect to the plane of the Pt It is likely that this orientation of the aromatic ligand rings is adopted to relieve the steric repulsion between the hydrogen atoms bonded on the ortho positions of the coordinated atoms.
An accurate description of the arrangement formed by the four platinum atoms is a parallelogram, since it is planar due to symmetry, the angles deviate significantly from 90 • , and the two diagonals are different, as shown in Table 1.
The lattice constituents interact with each other with a variety of supramolecular interactions involving π-π stacking between the 2,2 -bpy rings and non-conventional C-H• • • F H-bonds.There is a significant amount of void space in the structure (approximately 13.7% of the unit cell volume) which hosted some electron density that belongs probably to the crystallization solvents and could not be modeled.

Photophysical Studies 2.3.1. Absorption and Emission Spectra of (8)-(10)
Absorption and emission spectral data of the complexes (8)-(10) are summarized in Table 2. Figure 7a,b display the solid-state UV-vis absorption and emission spectra of ( 8)-(10).It is likely that this orientation of the aromatic ligand rings is adopted to relieve the steric repulsion between the hydrogen atoms bonded on the ortho positions of the coordinated atoms.An accurate description of the arrangement formed by the four platinum atoms is a parallelogram, since it is planar due to symmetry, the angles deviate significantly from 90°, and the two diagonals are different, as shown in Table 1.
The la ice constituents interact with each other with a variety of supramolecular interactions involving π-π stacking between the 2,2′-bpy rings and non-conventional C-H⋯F H-bonds.There is a significant amount of void space in the structure (approximately 13.7% of the unit cell volume) which hosted some electron density that belongs probably to the crystallization solvents and could not be modeled.
In acetonitrile solutions, the UV-vis spectra of the complexes ( 8)-(10) (Figure 7c) exhibit a broad band spanning the range of 250 to 400 nm, with their λmax values centered at 273, 295 and 315 nm, which can be assigned to intraligand transitions.Notably, the spectra's maxima demonstrate that shifts are proportional to the expansion of N,N′ ligand rings.This is particularly evident when introducing a phenyl ring, resulting in the anticipated red-shift [46].The molar absorbance coefficients for these complexes were calculated to fall within the range of 17 to 12 × 10 4 M −1 cm −1 , similar to those reported by Stang et al. for rhomboidal complexes featuring phenanthrene ligands [37].Complexes previously mentioned in the literature generally exhibit similar behavior, with their absorbance plateau extending up to 400 nm [37,39,40,47].However, a notable exception is found in a rhomboidal platinum complex with two -NH2 groups, substituted in 2,6-bis(4-pyridylethynyl)aniline, which displays an absorption band with λmax at 480 nm [37].The solid-state absorption spectra of ( 8)-(10) exhibit similar features, with the absorption bands observed at 200-350 nm attributed to intraligand transitions of the CˆC bph and N,N of 4,4-bpy, dpbz and dpbph.The lowest absorption bands at 442 (8), 425 nm (9), and 423 (sh) (10) are assigned to metal-to-ligand charge transfer [(5d)Pt→π*(L)] transitions [44].These absorption maxima follow the order (8) > ( 9) ≈ (10), and blue-shifted as the length of the BL increases, which can be attributed to the reduced CT efficiency caused by the increased length of the BL [45].
In acetonitrile solutions, the UV-vis spectra of the complexes ( 8)-(10) (Figure 7c) exhibit a broad band spanning the range of 250 to 400 nm, with their λ max values centered at 273, 295 and 315 nm, which can be assigned to intraligand transitions.Notably, the spectra's maxima demonstrate that shifts are proportional to the expansion of N,N ligand rings.This is particularly evident when introducing a phenyl ring, resulting in the anticipated red-shift [46].The molar absorbance coefficients for these complexes were calculated to fall within the range of 17 to 12 × 10 4 M −1 cm −1 , similar to those reported by Stang et al. for rhomboidal complexes featuring phenanthrene ligands [37].Complexes previously mentioned in the literature generally exhibit similar behavior, with their absorbance plateau extending up to 400 nm [37,39,40,47].However, a notable exception is found in a rhomboidal platinum complex with two -NH2 groups, substituted in 2,6-bis(4pyridylethynyl)aniline, which displays an absorption band with λ max at 480 nm [37].
Upon excitation at 400 nm, ( 8)-( 10) emit orange-red light with λ em centered at 602 (8), 581 (9) and 578 nm (10).The calculated Φ values range from 1.2 to 6.0.Again, a blueshift is observed upon increasing the BL length.In diluted acetonitrile solutions, the emission maxima of ( 8)-( 10) are observed at 646 (8), 667 (9) and 685 nm (10) with low Φ values (0.04-0.14%) (Figure 7c).The emission of complexes ( 8) and ( 9) is considerably red-shifted compared to most complexes mentioned in the literature, such as rhomboidal Pt(II) complexes with 2,6-bis(4-pyridylethynyl)aniline and anthracene, where λ em was found at approximately 400 and 500 nm accompanied by moderate Φ values [39].Among these, only the complex which has two -NH 2 groups, substituted in the ligand, and mentioned previously, exhibits an emission band centered at 581 nm and quantum yield smaller than 1%.A similar phenomenon is observed in parallelogram complexes with 1,4-bis(4-pyridylethynyl)benzene and p-Phtalic acid, where emission bands are centered at 390 nm [40].The excitation of samples at 400 nm produces an emission at approximately 600 nm, with a low quantum yield for complexes 9 and 10 (1%) and a moderate quantum yield for complex (11) (6%).In this case, a blue-shifting is observed due to the increase in aromaticity.The λ max are red-shifted by 50-100 nm compared to those in the solid state, indicating that the emission in the solid state is influenced by aggregation-induced phenomena possibly caused either by Pt• • • Pt interactions or/and by intermolecular ligand stacking [48], enhancing the quantum efficiency as well.However, contrary to the observation in the solid state, the emission λ max of ( 8)-( 10) in acetonitrile undergoes a red-shift upon increasing the BL length.
Transient photoluminescence measurements were carried out at 25 • C and λ exc = 325 nm, and the results are summarized at Table 3. Complexes ( 8)-( 10) have τ values that are about 10-100 times larger than parallelogram and rhomboidal ones reported in the literature [40,47]; however, they are within the normal range for organometallic compounds (10-700 ns) [49].The emission spectra of ( 8)-(10) were recorded in solvents with varying polarities to investigate their fluorosolvatochromic properties (Figure 8).The excitation wavelength λ exc.was kept constant at 365 nm for all cases.Complex (8) appears to be non-emissive in certain polar solvents such as DMF, EA, MeOH and THF.On the other hand, complexes ( 9) and (10) are emissive in all nine tested solvents, including methanol, wherein a bimodal emission pattern was observed.The emission band is located at orange region (590-614 nm) in slightly polar solvents, and red-shifted (620-670 nm) at highly polar solvents like methanol, acetone, acetonitrile and DMF.The results are presented in Table 4. Furthermore, in the spectrum of (10), the strongest emission is observed in CH 2 Cl 2 compared with the other solvents (Φ = 4%), similar to ( 8) and ( 9) in the same solvent.The red-shift of the λ em in highly polar solvents suggests that their excited states are more polarized than their ground states [41].
Molecules 2023, 28, x FOR PEER REVIEW 11 of 19 2.3.2.Solvent Effect on Emission Spectra of ( 8)-(10) The emission spectra of ( 8)-(10) were recorded in solvents with varying polarities to investigate their fluorosolvatochromic properties (Figure 8).The excitation wavelength λexc.was kept constant at 365 nm for all cases.Complex (8) appears to be non-emissive in certain polar solvents such as DMF, EA, MeOH and THF.On the other hand, complexes (9) and (10) are emissive in all nine tested solvents, including methanol, wherein a bimodal emission pa ern was observed.The emission band is located at orange region (590-614 nm) in slightly polar solvents, and red-shifted (620-670 nm) at highly polar solvents like methanol, acetone, acetonitrile and DMF.The results are presented in Table 4. Furthermore, in the spectrum of (10), the strongest emission is observed in CH2Cl2 compared with the other solvents (Φ = 4%), similar to ( 8) and ( 9) in the same solvent.The red-shift of the λem in highly polar solvents suggests that their excited states are more polarized than their ground states [41].2.3.3.Aggregation Effect and Emission Bimodal Spectra of ( 9) and (10) As previously mentioned, (Section 2.3.2) complexes ( 9) and (10) exhibit dual-emission spectra in MeOH, emitting at λ em 455/659 nm and 461/630 nm, respectively.Dual emitters have attracted considerable attention for various applications, such as fluorescent sensors [51], bioimaging [52], and single-molecule white light-emitting diodes [53] among others.For the latter, the tuning of the emission color may achieved by combining the λ em of a dual emitter with appropriate portions in different matrices [54].Aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ) are opposing phenomena [55].AIE refers to luminogenic compounds that are non-emissive when they are well dissolved in solvents as isolated molecules but become highly luminescent when they are aggregated in solvents with low solubility.AIE is the result of rapid energy dissipation by crossing a conical intersection in solutions, leading to low luminescence efficiencies and, in solids, intermolecular coupling, which effectively transfers energy and prevents quenching [56].On the other hand, ACQ refers toa reduction in emission intensity due to the aggregation of molecules into nanostructures, resulting in a smaller energy gap between the first singlet-excited state and the first triplet-excited state [57].
In order to investigate the influence of aggregation in dual emissions of the complexes (8) and ( 9), titrations of the complexes in methanol with a solvent capable of forming molecular aggregates, such as water, was carried out (Figure 9).In order to investigate the influence of aggregation in dual emissions of the complexes ( 8) and ( 9), titrations of the complexes in methanol with a solvent capable of forming molecular aggregates, such as water, was carried out (Figure 9).In the case of complex ( 9), as the percentage of H2O increases up to 50%, the intensity of the peak at 659 nm also increases, as well as the peak at 455 nm, which slightly blueshifted (Δν = 40 nm).This could be a ributed to the molecular aggregation of ( 9) due to hydrophobic interactions in a 1:1 mixture of water and methanol.Similar results have been In the case of complex (9), as the percentage of H 2 O increases up to 50%, the intensity of the peak at 659 nm also increases, as well as the peak at 455 nm, which slightly blue-shifted (∆ν = 40 nm).This could be attributed to the molecular aggregation of (9) due to hydrophobic interactions in a 1:1 mixture of water and methanol.Similar results have been reported by Fan et al., wherein the induced emission of a dual-emitter rhomboidal metallacycle in a solvent mixture of MeCN/hexane was attributed to the formation of aggregates [41].However, when the H 2 O percentage exceeds 50%, a sharp change in the spectrum is observed, followed by a significant blue-shift in the λ em emission (∆ν = 35 nm) and an increase in intensity.Simultaneously, the intensity of the orange emission significantly decreases.This sharp change may be attributed to the transition from the aggregate phase to the solid phase, through the precipitation of the complex in such a mixture of solvents.Similarly, in the case of complex (10), with increasing the percentage of H 2 O up to 40%, the intensity of the peak at 630 nm increases, and a blue-shift of ∆ν = 15 nm is observed, while the intensity of the peak at 461 nm increases but remains almost at the same λ em .This similarity with complex (9) suggests that the origin of the phenomenon is likely the same, originating from the molecular aggregation.The slight differences that appear are probably due to the differences in their size and solubility in MeOH/H 2 O, as the precipitation starts at relatively lower ratios MeOH:H 2 O [1:1 for (9) and 1:1.5 for (10)].When the H 2 O percentage exceeds 40%, a smoother change than in the case of ( 9) is observed.This is followed by a blue-shift of the λ em emission (∆ν = 15 nm) and a significant increase in intensity.Simultaneously, the intensity of the orange emission significantly decreases, reaching almost zero in 90% water, which may be attributed to the nearly complete precipitation of (10).
1 H NMR spectra of the ligands and the complexes were recorded using a Bruker Avance II spectrometer operating at a 1 H frequency of 500.13MHz or 400.13 MHz, and were processed using Topspin 4.2 (Bruker Analytik GmbH, Bremen, Germany).Two-dimensional COSY, TOCSY, and ROESY spectra were recorded following standard Bruker procedures.High-resolution electrospray ionization mass spectra (HR-ESI-MS) were obtained using a Thermo Scientific LTQ Orbitrap XL™ system.The UV-vis spectra of the complexes were recorded on an Agilent Cary 60 UV-vis spectrophotometer with a xenon source lamp in MeCN at room temperature.The fluorescence lifetime of complexes ( 8)-(10) was measured using an Edinburgh Mini-tau Lifetime Spectrometer.The sonication of the reaction between [Pt(bpy)Cl] 2 (µ-bph) and AgNO 3 in MeCN was achieved using a Sonics and Materials instrument.

Fluorescence Emission Studies
Emission studies were carried out using a Jasco FP-8300 fluorometer equipped with a xenon lamp source and an integrated sphere for solid samples.The relative quantum yield for solutions was determined using the equation Qs = Q r (A r /A s )(E s /E r )(n s /n r ) 2 , with a water solution of [Ru(bpy) 3 ]Cl 2 serving as the reference standard (Q r = 0.04).In this equation, 'A' represents the absorbance of the solutions, 'E' stands for the integrated fluorescence intensity of the emission spectrum, and 'n' denotes the refractive index of the solvents.Subscripts 'r' and 's' correspond to the reference and sample, respectively.The relative quantum yield of the solid-state complexes was calculated using the following equation: Q = S 2 /(S 0 − S 1 ), where 'Q' represents the quantum yield of the solid state of the complexes.In this equation, 'S 2 ' denotes the integrated emission intensity of the sample, while 'S 0 ' and 'S 1 ' refer to the excitation intensities of the standard and the sample, respectively.

X-ray Crystallography
Crystals from compound 8 were grown via slow vapor diffusion of diethyl ether in an acetonitrile solution of the prepared complex.
A suitable crystal of approximate dimensions 0.02 × 0.06 × 0.12 mm 3 was glued to a thin glass fiber with cyanoacrylate (super glue) adhesive and placed on the goniometer head.Diffraction data were collected on a Bruker D8 Quest Eco diffractometer, equipped with a Photon II detector and a TRIUMPH (curved graphite) monochromator utilizing Mo Kα radiation (λ = 0.71073 Å) using the APEX3 software package [58].The collected frames were integrated with the Bruker SAINT software using a wide-frame algorithm.Data were corrected for absorption effects using the multi-scan method (SADABS) [59].The structure was solved using the Bruker SHELXT Software Package and refined via full-matrix leastsquares techniques on F2 (SHELXL 2018/3) [60] via the ShelXle interface [61].The non-H atoms were treated anisotropically, while the organic H atoms were placed in calculated, ideal positions and refined as riding on their respective carbon atoms.
Details on data collection and refinement are presented in Table S1.Full details on the structures can be found in the CIF files deposited with CCDC.CCDC 2296015 contains the supplementary crystallographic data for this paper.

Conclusions
Platinum(II) supramolecular coordination complexes (SCCs) ( 8)-(10) were synthesized using a stepwise method and fully characterized.The structural features of ( 8)-( 10) indicate that they have a rectangular shape, especially complex (8), while complexes ( 9) and ( 10) can be referred to as parallelograms with four platinum atoms at the corners.This is also confirmed by the crystal structure of (8).The complexes' emission spectra in solution showed a strong dependence on solvent polarity.Complexes ( 9) and (10) exhibited dual emission in MeOH, while (8) was non-emissive.Furthermore, ( 9) and (10) exhibited aggregation-induced emission (AIE) and quenching-induced emission (QIE) phenomena upon aggregation in MeOH/H 2 O solutions.
Funding: Antonia Garypidou and Konstantinos Ypsilantis were financially supported by the project "Center For Research, Quality Analysis Of Cultural Heritage Materials and Communication Of Science" (MIS 5047233) implemented under the Action "Reinforcement of the Research and Innovation Infrastructure", funded by the Operational Program "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund).

Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.

Molecules 2023 ,
28,  x FOR PEER REVIEW 12 of 19 aggregated in solvents with low solubility.AIE is the result of rapid energy dissipation by crossing a conical intersection in solutions, leading to low luminescence efficiencies and, in solids, intermolecular coupling, which effectively transfers energy and prevents quenching[56].On the other hand, ACQ refers toa reduction in emission intensity due to the aggregation of molecules into nanostructures, resulting in a smaller energy gap between the first singlet-excited state and the first triplet-excited state [57].

Figure 9 .
Figure 9. (a) Emission spectrum of complex (9) increasing in a mixture of MeOH/H2O in different ratios.(b) Emission spectrum of complex (10) increasing in a mixture MeOH/H2O in different ratios.

Figure 9 .
Figure 9. (a) Emission spectrum of complex (9) increasing in a mixture of MeOH/H 2 O in different ratios.(b) Emission spectrum of complex (10) increasing in a mixture MeOH/H 2 O in different ratios.