New members of the family of highly luminescent 1,3-bis(4-phenylpyridin-2-yl)-4,6-difluorobenzene platinum(II) complexes: exploring the effect of substituents on the 4-phenylpyridine unit

Abstract

The synthesis and characterization of Pt{1,3-bis(4-phenylpyridin-2-yl)-4,6-difluorobenzene}Cl and Pt{1,3-bis(4-(4-methoxy-2,6-dimethylphenyl)-pyridin-2-yl)-4,6-difluorobenzene}Cl are reported, along with their molecular structure optimized by Density Functional Theory. These new NCN-coordinated Pt(II) complexes are both very highly luminescent in deoxygenated solution in the blue region of the spectrum: λ_max = 471–480 nm and Φ_lum = 0.89–0.98 at room temperature. Compared to the Pt{1,3-bis(pyridin-2-yl)-4,6-difluorobenzene}Cl analogue, the complex with a simple, unsubstituted phenyl ring at position 4 of the pyridinyl rings shows an improved luminescence quantum yield. However, a further enhancement is achieved with the 2,6-dimethyl-4-methoxyphenyl substituent, the steric hindrance of which inhibits the formation of bimolecular species, allowing high quantum yields to be maintained even in concentrated solutions (2 × 10⁻⁴ M).

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Introduction

Luminescent platinum(II) complexes are extensively researched owing to their potential for application in nonlinear optics,^1–8 bioimaging,^9–25 sensing,^26–28 photocatalysis,^29–31 and electro-luminescent devices.^32–46 The strong spin–orbit coupling (SOC) associated with the platinum atom promotes intersystem crossing to triplet excited states and their subsequent radiative decay by relaxing the spin selection rule. The phosphorescence is typically favoured by the introduction of platinum–carbon bonds within cyclometallated units, as the resulting strong ligand fields ensure that otherwise deactivating d–d excited states are destabilised, and non-radiative decay through them is suppressed.^47,48 Unlike complexes of d⁶ metal ions such as Ir(III), the square planar geometry favours the formation of bimolecular states – either in the ground state (dimers or higher aggregates) or in the excited state (excimers) – thanks to Pt⋯Pt or ligand⋯ligand intermolecular interactions. These species may emit at lower energies than the isolated molecules, offering an intriguing route to deep-red/NIR-emitting materials, colour modulation according to the local concentration, and even white light emission.^{42,43,49–51}

Pt(II) complexes of the NCN-coordinating ligand 1,3-bis(pyridin-2-yl)benzene (dpyb) are among the brightest and most efficient Pt-based emitters, apparently owing to the combination of a particularly short Pt–C bond and high rigidity, minimising non-radiative decay.^52–55 Recently, some of us studied the effect of the introduction of a polarizable π-delocalized bulky substituent on the phosphorescence properties of Pt(F₂dpyb)Cl {F₂dpybH = 1,3-bis(pyridin-2-yl)-4,6-difluorobenzene},⁵⁶ demonstrating particularly high quantum yields for PtL¹Cl and PtL²Cl {Scheme 1; HL¹ = 1,3-bis(4-triphenylamine-pyridin-2-yl)-4,6-difluoro-benzene and HL² = 1,3-bis(4-mesityl-pyridin-2-yl)-4,6-difluoro-benzene}.^57,58 In this context, we were curious to see the effect of the introduction of other π-delocalized groups on the 4-position of the pyridine rings. Here we describe the synthesis and properties of the complex with a simple unsubstituted phenyl group on each pyridine ring (PtL³Cl, Scheme 1) and the related complex with a 2,6-dimethyl-4-methoxyphenyl group (PtL⁴Cl). Both are highly emissive, enlarging this fascinating, brightly luminescent family of complexes based on NCN ligands that feature 4-phenylpyridin-2-yl units.

Scheme 1 Chemical structures of the investigated complexes.

Results and discussion

Preparation of the new pro-ligands HLⁿ and of the related Pt(II) complexes

The new proligand 1,3-bis(4-phenylpyridin-2-yl)-4,6-difluoro-benzene (HL³) was prepared by Pd-catalysed cross-coupling of the pinacol ester of 1,3-difluoro-4,6-diboronic acid⁵⁸ with 2-chloro-4-phenylpyridine. 1,3-Bis(4-(4-methoxy-2,6-dimethyl-phenyl)-pyridin-2-yl)-4,6-difluorobenzene (HL⁴) was prepared similarly using 2-chloro-4-(2,6-dimethyl-4-methoxyphenyl)-pyridine (Scheme 2). The two chlorinated reagents were likewise prepared by cross-couplings, as shown in Scheme 2. Reaction of the proligands with K₂PtCl₄ led to PtL³Cl and PtL⁴Cl in 93% and 81% yield, respectively. Full details of synthesis and characterisation are provided in the Experimental Section and in the ESI.†

Scheme 2 Synthesis of PtL³Cl and PtL⁴Cl.

Photophysical properties

The absorption spectra of PtL³Cl and PtL⁴Cl in dichloromethane at selected concentrations between 1 × 10⁻⁶ and 1 × 10⁻⁴ M are shown in Fig. 1. There are intense bands in the range 260–320 nm, due to intraligand ¹π–π* transitions of the NCN ligand, and less intense bands at 340–420 nm, due to charge-transfer transitions involving the cyclometalated ligand and the metal, as for related NCN-coordinated platinum(II) complexes.^55–59 A weaker band at 471 and 467 nm (ε = 262 and 214 M⁻¹ cm⁻¹) for PtL³Cl and PtL⁴Cl, respectively (Fig. 1, insets), is attributed to the weak transition from the singlet ground state to the lowest triplet state. This formally spin forbidden S₀ → T₁ transition, facilitated by the high SOC associated with the Pt centre, is close to that of the parent Pt(F₂dpyb)Cl (467 nm, 140 M⁻¹ cm⁻¹). The higher extinction coefficient for this transition in PtL³Cl and PtL⁴Cl may be an indication of more efficient SOC pathways.

Fig. 1 Absorption spectra of PtL³Cl (a) and PtL⁴Cl (b) at the concentrations indicated, in CH₂Cl₂ at 298 K. The weak bands at longer wavelengths are shown on an expanded scale in the insets, for clarity.

The normalized emission spectra of PtL³Cl and PtL⁴Cl at various concentrations in degassed CH₂Cl₂ solution at room temperature are shown in Fig. 2 (see also Fig. S4–S8 and S18–S22 in the ESI†). Upon excitation at 380 nm in dilute solution (1 × 10⁻⁶ M), PtL³Cl displays a structured spectrum, λ^0,0 = 480 nm, with a vibrational progression of around 1400 cm⁻¹, attributed to emission from the T₁ state.⁵⁶ The corresponding band of PtL⁴Cl is a little blue-shifted to 471 nm, very similar to that reported for the mesityl analogue PtL²Cl⁵⁸ and for Pt(F₂dpyb)Cl.⁵⁶ In contrast, the previously investigated triphenylamine-substituted complex PtL¹Cl displayed much lower-energy emission, with λ_max = 562 nm.⁵⁷

Fig. 2 Normalized emission spectra of PtL³Cl (a; λ_ex = 380 nm) and PtL⁴Cl (b; λ_ex = 377 nm) in degassed dichloromethane solution at the concentrations indicated, at 298 K.

For PtL³Cl, as the concentration is increased, a broad, structureless band progressively grows in, with λ_max around 704 nm (Fig. 2a), attributed to the formation of emissive, bimolecular excited states (excimers and/or aggregates).⁵⁹ For PtL⁴Cl, the corresponding band – centered at 680 nm in this case – is much less intense at a given concentration (compare Fig. 2a and b), probably due to the steric hindrance of the 4-methoxy-2,6-dimethyl phenyl substituent on the pyridyl rings. The presence of the two methyl groups ortho to the interannular C–C bond will inhibit the attainment of the planar conformation that favours face-to-face intermolecular interactions. The corresponding band was similarly weak in the mesityl-substituted PtL²Cl.⁵⁸

Under the same conditions, PtL¹Cl, PtL²Cl, and Pt(F₂dpyb)Cl are bright Pt(II) emitters with reported luminescence quantum yields (Φ_lum) of 0.90,⁵⁷ 0.97,⁵⁸ and 0.80,⁵⁶ respectively. PtL³Cl and PtL⁴Cl are similarly here to be characterized by excellent quantum yields of 0.89 and 0.98, respectively, as determined with an integrating sphere (Table 1). Under air-equilibrated conditions, the Φ_lum values decrease to 0.28 and 0.16, respectively, due to oxygen quenching; given the efficacy of this quenching, efficient production of singlet oxygen can be anticipated, an interesting aspect for photodynamic therapy.¹⁹

Table 1 Photophysical parameters of PtL³Cl and PtL⁴Cl, with those of PtL¹Cl⁵⁷ and PtL²Cl⁵⁸ also reported for comparison

Parameter^a	PtL^1Cl	PtL^2Cl	PtL^3Cl	PtL^4Cl
a At a concentration of 5 × 10^−6 M at 298 K in degassed CH2Cl2, unless otherwise indicated. b λ ex = 422, 334, 380, and 377 nm for PtL^1Cl, PtL^2Cl, PtL^3Cl, and PtL^4Cl, respectively. c λ max of the excimer at 1.9 × 10^−4 M. d φ lum measured with an integrating sphere. e Radiative and non-radiative rate constants are calculated from the quantum yields and emission decay times according to kr = Φlum/τ and knr = (1 − Φlum)/τ.
λ max,abs S0 → T1/nm [ε/M^−1 cm^−1]	Not detected	467 [120]	471 [277]	467 [214]
λ max,em/nm^b monomer [excimer]^c	562 [696]	471 [680]	480 [704]	471 [680]
Φ lum [aerated]	0.90 [0.059]	0.97 [0.18]	0.89 [0.28]	0.98 [0.16]
Φ lum (1.9 × 10^−4 M)^d [aerated]	0.66 [0.026]	0.62 [0.12]	0.53 [0.22]	0.85 [0.13]
τ/μs	104	4.8	3.5	4.5
τ/μs (1.9 × 10^−4 M)	4.3	2.4	0.93	4.0
k r  /s^−1	8.7 × 10^3	2.0 × 10^5	2.5 × 10^5	2.2 × 10^5
k r  ^e/s^−1 (1.9 × 10^−4 M)	1.5 × 10^5	2.6 × 10^5	5.7 × 10^5	2.1 × 10^5
k nr  /s^−1	96 × 10^2	6.3 × 10^3	3.1 × 10^4	4.4 × 10^3
k nr  ^e/ s^−1 (1.9 × 10^−4 M)	7.7 × 10^4	1.6 × 10^5	5.1 × 10^5	3.7 × 10^4

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The formation of excimers and aggregates of Pt(NCN)Cl complexes typically comes at the expense of the quantum yields.⁵⁵ For PtL³Cl and PtL⁴Cl, increasing the concentration does compromise the quantum yield, but only to a very modest extent: for instance, the values at 1.9 × 10⁻⁴ M remain remarkably high (0.53 and 0.85, respectively). Inspection of the values in Table 1, in the context also of PtL^1,2Cl, indicates that Φ_lum for PtL⁴Cl is substantially less affected by concentration than the other three complexes. Apparently, the steric hindrance of the 4-methoxy-2,6-dimethyl phenyl substituents to the formation of bi-molecular emissive species – as noted above based on the low intensity of the low-energy excimer band – also ensures that excellent quantum yields are maintained, even at elevated concentrations.

In the literature, methods to determine the luminescence quantum yields can be divided into two main approaches: the use of an integrating sphere, or the use of standards relative to which the intensity of emission is compared.⁶⁰ We were curious to compare the Φ_lum values measured by means of an integrating sphere (Table 1) with those obtained relative to different standards. By using Pt(dpyb)Cl as the standard (Φ_lum = 0.60 in degassed CH₂Cl₂, λ^em_max = 491 nm),⁵² we determined Φ_lum values of 0.83 and 0.93 for PtL³Cl and PtL⁴Cl, respectively, in good agreement with the values measured with the integrating sphere. By using [Ru(bpy)₃]Cl₂ as standard (Φ_lum = 0.04 in aerated H₂O; λ^em_max = 628 nm),⁶⁰ values of 0.84 and 0.71, respectively, were determined. We consider Pt(dpyb)Cl to be the more reliable standard, owing to the better match of the emissive regions and to a more comparable quantum yield.

Excited state decay measurements of PtL³Cl in degassed CH₂Cl₂ solutions at different concentrations were performed, exciting at 374 nm and monitoring the emission at 480 nm (ESI, Table S2 and Fig. S9–S13†). The longest lifetime, 3.8 μs, is observed at the lowest concentration (1 × 10⁻⁶ M). An increase of the concentration leads to a decrease of the lifetime (3.5 and 3.3 μs at 5 × 10⁻⁶ and 1 × 10⁻⁵ M, respectively), a much lower value (0.93 μs) being obtained at 1.9 × 10⁻⁴ M. A linear Stern–Volmer relationship is observed, with a self-quenching constant k_Q of 4.3 × 10⁹ M⁻¹ s⁻¹ determined from the gradient, consistent with excimer formation (i.e., diffusion-controlled excited-state quenching as opposed to ground-state aggregation). Moreover, the temporal evolution of the emission intensity of the most concentrated solution at 704 nm clearly shows an initial rise at short time intervals, associated with the formation of excimers, with a τ of 0.7 μs (Fig. S14 in the ESI†). Corresponding measurements were made for PtL⁴Cl, monitoring the emission intensity at 471 nm (ESI, Table S4 and Fig. S23–S27†). Again, the longest lifetime, 4.6 μs, is observed at the lowest concentration (1 × 10⁻⁶ M). In this case, the lifetime is only marginally reduced over the entire concentration range investigated (τ = 4.6, 4.5, 4.2 and 4.0 μs at 2.5 × 10⁻⁶, 5 × 10⁻⁶, 1 × 10⁻⁵, and 1.9 × 10⁻⁴ M, respectively), consistent with high quantum yields being maintained at high concentrations, and with the excimer band having almost negligible intensity. In this instance, the change in lifetime is simply too small to determine the self-quenching constant reliably. However, for the most concentrated solution, the emission intensity again shows an initial rise at short time intervals after excitation (Fig. S28†), from which a time constant for excimer formation of 1.5 μs was estimated. The process is thus evidently slower than for PtL³Cl. The effect of the 4-methoxy-2,6-dimethyl groups in hindering self-quenching and excimer formation is apparently rather larger than that associated with the mesityl groups in PtL²Cl, wherein the lifetime declined to a greater extent with concentration (Table 1).⁵⁸ As expected, the presence of substituents on the phenyl rings of the pyridine rings reduces the propensity to form bimolecular species (see Fig. S29 in the ESI† for the plot of intensity of the lowest energy band vs. concentration).

The very long lifetime observed in the case of PtL¹Cl, with a triphenylamine group on the pyridines, remains unique amongst the four complexes.⁵⁷

Radiative k_r and non-radiative k_nr decay constants can be estimated from the Φ_lum and τ values, assuming that the emitting state is formed with unit efficiency. It is clear from the values so calculated (Table 1) that the superior quantum yield of PtL⁴Cl compared to PtL³Cl originates from suppressed non-radiative processes in the former, both in dilute and concentrated solution. Meanwhile, the k_r values of PtL^2–4Cl are ≥2 × 10⁵ s⁻¹, around 3× that of the parent unsubstituted complex Pt(dpyb)Cl, and approaching that of the “gold standard” fac-Ir(ppy)₃, for which k_r is around 4 × 10⁵ s⁻¹.³⁸ It is likely that the higher energy of the emissive triplet state in PtL^2–4Cl leads to a smaller S₁–T₁ energy gap ΔE_S–T, and hence to more efficient promotion of the formally forbidden T₁ → S₀ transition (the efficiency of which is inversely related to ΔE_S–T⁴⁷). The ΔE_S–T values estimated from the maxima of the lowest-energy absorption bands and the 0,0 component of the emission are approximately 5900 cm⁻¹ for PtL¹Cl, compared to lower values of 5100 for PtL²Cl, and 5300 cm⁻¹ for PtL³Cl and PtL⁴Cl. Of course, relaxation of the spin selection rule also requires efficient mixing of metal orbitals into the excited state, to benefit from the high spin–orbit coupling associated with the metal. TD-DFT calculations on related complexes reveal heavily-mixed d_Pt|π_L → π_L* states.^61,62 On the other hand, the electron-rich anilino pendants in PtL¹Cl likely render the lowest-energy excited states of intraligand character (i.e., π_Ar → π_py*, where Ar = Ph₂N–C₆H₄–), suppressing the degree of metal character and leading to an abnormally low k_r and long observed lifetime τ.⁶¹

Computational modelling

To model the molecular structure of PtL³Cl and PtL⁴Cl, we turned to geometry optimization by Density Functional Theory (DFT). DFT calculations were performed both on the isolated complexes and on the related dimers. The dimers can be considered the simplest representative species of the aggregation phenomenon that may provide information on the packing of PtL³Cl and PtL⁴Cl in the crystal and the aggregation in solution. The monomer and the dimer geometry optimizations were performed with the Gaussian09 program package (G09)⁶³ by using the B3LYP exchange–correlation functional⁶⁴ integrated with the D3-BJ model⁶⁵ to include the dispersion effects in the geometry optimizations. The dichloromethane solvation effects were included through the conductor-like polarizable continuum model as implemented in G09.^66–69 All the atoms, except Pt, were described by 6-31G** basis set,^70–72 while Pt was described with the LANL2DZ basis set along with the corresponding pseudopotentials.⁷³ Such computational methodology has been demonstrated to be accurate for reproducing the geometry of the PtL²Cl complex and its aggregation phenomena in solution; moreover the optimized dimer structure calculated in solution mimics the main orientation of the PtL²Cl molecules in the crystal.⁵⁸ In Fig. 3 and 4 the optimized molecular geometries of both PtL³Cl and PtL⁴Cl monomer and dimer, respectively, are reported, showing both the front and side views for the dimers. As already observed for (PtL²Cl)₂,⁵⁸ in (PtL³Cl)₂ and (PtL⁴Cl)₂ the two monomers are arranged in a head-to-tail configuration with respect to the Pt centers being staggered one from the other. In (PtL³Cl)₂ and (PtL⁴Cl)₂ the Pt⋯Pt distance is computed to be 4.88 Å and 6.54 Å, respectively, compared to a value of 6.31 Å for (PtL²Cl)₂. In (PtL³Cl)₂ the presence of unsubstituted phenyls allows for a closer approach of the two monomeric units; on the contrary, in (PtL⁴Cl)₂, the methoxy substituent in place of methyl in para position slightly increases the Pt⋯Pt distance.

Fig. 3 Optimized molecular geometries of the monomer and dimer of PtL³Cl in dichloromethane. Both the front and side view have been shown for the dimer.

Fig. 4 Optimized molecular geometries of the monomer and dimer of PtL⁴Cl in dichloromethane. Both the front and side view have been shown for the dimer.

The dimerization energy for the formation of (PtL³Cl)₂ in dichloromethane is computed to be slightly smaller than for (PtL²Cl)₂ −43.34 kcal mol⁻¹vs. −47.4 kcal mol⁻¹, while that computed for (PtL⁴Cl)₂ in solution is slightly larger, at −50.5 kcal mol⁻¹. The dimerization energy provides an estimate of π⋯π and Pt⋯Pt interactions that allow the dimer to form.

Conclusion

In conclusion, two novel members of the family of 1,3-bis(4-phenylpyridin-2-yl)-4,6-difluoro-benzene Pt(II) complexes were easily prepared and well characterized. Both are highly luminescent (Φ_lum = 0.89–0.98) in the blue region (471–480 nm) with lifetimes of a magnitude typical for Pt(dpyb)Cl derivatives (ca. 4 μs). It appears that the introduction of a simple phenyl group on the position 4 of the pyridine rings is a useful way to improve the luminescence quantum yield of the parent complex Pt(F₂dpyb)Cl. A further enhancement can be achieved with a suitable functionalization of the 4-phenylpyridine moiety. Thus, this work shows that the steric hindrance of the 4-methoxy-2,6-dimethyl phenyl moiety on the pyridinyl rings is particularly appropriate, and even better than that of a triphenylamine or mesityl group in hampering the formation of bimolecular species. It allows excellent quantum yields to be maintained even in concentrated solutions, an aspect of particular interest in future applications.

Experimental section

General comments

All reagents and solvents were used as received from the supplier. The purifications were performed through column chromatography on silica gel (Merck Geduran 60, 0.063–0.200 mm).

NMR characterizations were obtained recording on a Bruker AV III 300 MHz or AV III 400 MHz spectrometers. Chemical shifts of ¹H, ¹⁹F and ¹³C NMR spectra are reported in parts per million (ppm) and the coupling constants are measured in Hertz (Hz). The multiplicities of signals are listed as singlet (s), d (doublet), t (triplet), quartet (q), multiplet (m).

UV-Visible spectra were collected by a Shimadzu UV3600 spectrophotometer. Luminescence measurements were carried out in CH₂Cl₂ solution after the Freeze–Pump–Thaw (FPT) procedure necessary to remove dissolved oxygen. Photoluminescence quantum yields, Φ_lum, were measured using a C11347 Quantaurus Hamamatsu Photonics K.K spectrometer (see ESI† for details) or relative to the standards indicated earlier.

Steady state and time-resolved fluorescence data were obtained using a FLS980 spectrofluorimeter (Edinburg Instrument Ltd). Emission spectra were corrected for background intensity and quantum efficiency of the photomultiplier tube. Excitation spectra were corrected for the intensity fluctuation of a 450 W Xenon arc lamp. Time-resolved fluorescence measurements were performed through the time-correlated single photon counting technique with an Edinburgh Picosecond Pulsed Diode Laser (emitted wavelength 374 nm).

Synthesis of PtL³Cl

HL³ (0.10 g, 0.24 mmol) was dissolved in acetonitrile (9 mL) and a solution of K₂PtCl₄ (0.16 g, 0.38 mmol) in water (1 mL) was added. Before sealing the flask, the reaction mixture was degassed by bubbling argon through the solution for 30 minutes. The mixture was heated at 110 °C for 72 h. The obtained suspension was allowed to cool to room temperature and was filtered through a 0.45 μm Nylon membrane. The collected solid was then washed with water, MeOH and diethyl ether, and dried under vacuum to obtain the desired Pt complex as a yellow powder (121 mg, 93% yield). ¹H-NMR (300 MHz, CDCl₃, δ): 9.32 (d, J = 6.1 Hz, ³J(¹⁹⁵Pt) = 41 Hz, 2H), 8.11 (s, 2H), 7.69–7.78 (m, 4H), 7.58 (dd, J = 8.9, 5.0 Hz, 6H), 7.49 (dd, J = 6.0, 1.9 Hz, 2H), 6.77 (t, J = 11.3 Hz, 1H). ¹⁹F {¹H} NMR (282.36 MHz, CDCl₃, δ): −108.30 (s, ³J(¹⁹⁵Pt) = 43 Hz, 2F). ¹³C {¹H} NMR (75.48 MHz, CDCl₃, δ): 151.8, 136.7, 130.3, 129.4, 127.2, 120.7, 120.4. Elemental anal. calcd for C₂₈H₁₇ F₂N₂¹⁹⁵Pt³⁵Cl: C, 51.74; H, 2.64; N, 4.31; Cl, 5.45; F, 5.85, Pt, 30.01; found: C, 51.83; H, 2.67; N, 4.33.

Synthesis of PtL⁴Cl

HL⁴ (0.14 g, 0.27 mmol) was dissolved in acetonitrile (11.7 mL) and a solution of K₂PtCl₄ (0.22 g, 0.53 mmol) in water (1.3 mL) was added. Argon was bubbled through the mixture for 40 minutes before sealing the reaction vessel. The reaction mixture was heated to 110 °C for 72 h. The obtained suspension was allowed to cool to room temperature and then filtered through a 0.45 μm Nylon membrane. The collected solid waswashed with water, MeOH and diethyl ether, and dried under vacuum to obtain the desired Pt complex as a yellow powder (124 mg, 81%). ¹H-NMR (300 MHz, CDCl₃, δ): 9.40 (d, J = 5.9 Hz, ³J(¹⁹⁵Pt) = 40 Hz, 2H), 7.76 (s, 2H), 7.17 (d, J = 5.8, 2H), 6.68–6.80 (m, 5H), 3.87 (s, 6H), 2.13 (s, 12H). ¹³C{¹H}-NMR (75.48 MHz, CDCl₃, δ): 164.2, 159.4, 153.8, 151.9, 136.3, 130.7, 124.9, 124.1, 113.3, 55.2, 21.2. ¹⁹F{¹H}-NMR (282 MHz, CDCl₃, δ): −108.1 (s, 2F). HRMS (ESI⁺): (M + Na)⁺ calcd for C₃₄H₂₉N₂O₂F₂³⁵Cl Na¹⁹⁵Pt, 788.1426; found: 788.1436. Elemental anal. calcd for C₃₄H₂₉ClF₂N₂O₂Pt: C, 53.30; H, 3.82; N, 3.66; found: C, 53.55; H, 3.83; N, 3.64.

Author contributions

Conceptualization, D.R. and V.G.; methodology, B.C., D.M., A.C., C.D., F.F., S.F.; investigation, G.D., D.M., F.F., J.A.G.W., S.F.; resources, A.C. and C.D.; data curation, G.D., D.M., F.F., J.A.G.W., S.F.; supervision, D.R. and V.G.; writing—original draft, F.F.; writing—review and editing, G.D., B.C., V.G., J.A.G.W., D.M., A.C., C.D., F.F., S.F., D.R. All authors have read and agreed to the published version of the manuscript.

Data availability

The data supporting this article, including details on the synthesis and full characterization of the two complexes (¹H, ¹³C, and ¹⁹F NMR spectra, HRMS, elemental analysis, photophysical characterization), computational modelling have been included as part of the ESI.†

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

Fondazione Cariplo and Regione Lombardia are acknowledged for the instrumentation bought during the SmartMatLab Centre project (2014). The work was supported by the National Interuniversity Consortium of Materials Science and Technology (Project TRI_25_073 Dragonetti and TRI_25_173 Colombo) and Università di Milano (Project PSR2023_DIP_005_PI_FTESS).

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d5dt00682a

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