Pt(II) Complexes with Tetradentate C^N*N^C Luminophores: From Supramolecular Interactions to Temperature-Sensing Materials with Memory and Optical Readouts

A series of four regioisomeric Pt(II) complexes (PtLa-n and PtLb-n) bearing tetradentate luminophores as dianionic ligands were synthesized. Hence, both classes of cyclometallating chelators were decorated with three n-hexyl (n = 6) or n-dodecyl (n = 12) chains. The new compounds were unambiguously characterized by means of multiple NMR spectroscopies and mass spectrometry. Steady-state and time-resolved photoluminescence spectroscopy as well quantum chemical calculations show that the effect of the regioisomerism on the emission colour and on the deactivation rate constants can be correlated with the participation of the Pt atom on the excited state. The thermal properties of the complexes were studied by DSC, POM and temperature-dependent steady-state photoluminescence spectroscopy. Three of the four complexes (PtLa-12, PtLb-6 and PtLb-12) present an intriguing thermochromism resulting from the responsive metal–metal interactions involving adjacent monomeric units. Each material has different transition temperatures and memory capabilities, which can be tuned at the intermolecular level. Hence, dipole–dipole interactions between the luminophores and disruption of the crystalline packing by the alkyl groups are responsible for the final properties of the resulting materials.

Several Pt(II)-based species with sensing applications rely on their capability to form aggregates, both in solution and in the solid state.The formation of Pt(II)-based aggregates is possible due to their planar coordination geometry and is mainly driven by van der Waals interactions.When the distance between the Pt atoms is approximately 3.5 Å or shorter (i.e., below the sum of their van der Waals radii), coupling between the d z 2 orbital lobes protruding out of the coordination plane becomes feasible.The resulting aggregates show a red-shifted emission if compared with the monomeric species, which arises from triplet metal-metal-to-ligand charge transfer ( 3 MMLCT) states with a certain degree of excimeric character [14,21,31,32].Hence, we have now prepared a series of Pt(II) complexes where the modification in the length and position of peripheral alkyl chains allows us to control the photophysical properties, the characteristics of the solid phase and the transition temperatures of the resulting solids.These concepts can lead to temperature-sensing materials with memory based on Pt-Pt interactions and providing optical readouts.
The complexes presented in this work have been developed as a natural progression of our previous research [4].The herein-reported replacement of the methoxyphenyl group at the bridging N-atom by alkyl chains aims at promoting the aggregation of the complexes.This stacking was partially hampered in our previous complexes, due to the 90 • rotation of the phenyl ring with respect to the luminophoric plane [4,14].In addition, modulation of the length and position of the alkyl chains affects the packing and supramolecular interactions between the molecular units in the solid state, leading to changes in the thermal properties of the complexes.

Synthesis
The synthesis of the ligands (Scheme 1) started with the reaction between 2,6dibromopyridine and 2-amino-6-bromopyridine promoted by NaH to give the precursor 1.The intermediate 1 was reacted with 1-bromohexane or 1-bromododecane to yield the precursors 2-6 and 2-12, respectively.A further Suzuki-Miyaura cross-coupling with an excess of the corresponding hydroxyphenylboronic acid allowed us to prepare the intermediates 3a-n and 3b-n (n = 6 or 12).The phenolic species were not isolated and the ligands L a -n and L b -n were finally obtained by Williamson's ether synthesis using the corresponding alkylbromide [4].The Pt(II) complexes were prepared by a standard cycloplatination reaction with K 2 PtCl 4 in acetic acid at reflux with yields between 30 and 44%, which are in agreement with previously reported syntheses [4,14].The comparable yields obtained for both regioisomers suggest that, in the case of PtL b -n complexes, only one of the three potential cyclometallation products is formed.This result may be attributed to the steric hindrance imposed by the alkyl chains during the cycloplatination reaction.The complexes show a good solubility in polar organic solvents, such as DCM and THF, mostly due to the presence of the peripheral alkyl chains [4].All the precursors and complexes were unambiguously characterized by means of 2D-NMR (including a full assignment of 1 H and 13 C signals) as well as by high-resolution mass spectrometry (Figures S1-S61).Further experimental details can be found in the ESI.

Photophysics in Diluted Conditions
The photophysical characterization of the complexes was initially performed in diluted DCM solutions (complex concentration c ≈ 10 −5 M) at room temperature.The absorption bands in the region between 235 and 300 nm can be assigned to transitions into 1 LC states, while the bands in the region between 350 and 450 nm are related to mixed singlet states with variable degrees of LC and MLCT character, as was previously reported for comparable complexes (Figure 1 left, Figure S62 and Table S1) [14,21,[33][34][35].Interestingly, the PtL b -n complexes present a stronger absorption band in the 1 MLCT (≈420 nm) region if compared with the PtL a -n complexes.This can be attributed to the higher contribution of the alkoxy group in para position (with respect to the Pt atom) to the HOMO than in case of the moiety in meta position, and therefore to a higher destabilization of the HOMO (as previously observed for Ir(III) complexes and [36,37] in phenylpyridine Pt(II)-based complexes [38]).
The emission spectra of the PtL a -n complexes (Figure 1 right, Figure S63) show a maximum at 517 nm with vibrational shoulders at 553 nm, which arise mainly from 3 MP-LC states [14,33,34,39].The spectra of PtL b -n are red-shifted with a maximum at 555 nm (Figure 1 right, Figure S64).The red shift in the emission can be also ascribed to a destabilization of the HOMO and consequently to a reduction in the gap between the excited and ground state [37,38].To support and interpret the experimental results, (TD-)DFT calculations were performed for the methoxy-substituted complexes (PtL a -1 and PtL b -1) as model compounds.After the geometry optimization of the ground state (S0) and the lowest triplet state (T1) was achieved, the emission maxima were calculated (Figure S77) [40][41][42][43][44][45][46][47].

Photophysics in Diluted Conditions
The photophysical characterization of the complexes was initially performed in diluted DCM solutions (complex concentration c ≈ 10 −5 M) at room temperature.The absorption bands in the region between 235 and 300 nm can be assigned to transitions into 1 LC states, while the bands in the region between 350 and 450 nm are related to mixed singlet states with variable degrees of LC and MLCT character, as was previously reported for comparable complexes (Figure 1 left, Figure S62 and Table S1) [14,21,[33][34][35].Interestingly, the PtL b -n complexes present a stronger absorption band in the 1 MLCT (≈420 nm) region if compared with the PtL a -n complexes.This can be attributed to the higher contribution of the alkoxy group in para position (with respect to the Pt atom) to the HOMO than in case of the moiety in meta position, and therefore to a higher destabilization of the HOMO (as previously observed for Ir(III) complexes and [36,37] in phenylpyridine Pt(II)-based complexes [38]).

Photophysics in Diluted Conditions
The photophysical characterization of the complexes was initially performed in diluted DCM solutions (complex concentration c ≈ 10 −5 M) at room temperature.The absorption bands in the region between 235 and 300 nm can be assigned to transitions into 1 LC states, while the bands in the region between 350 and 450 nm are related to mixed singlet states with variable degrees of LC and MLCT character, as was previously reported for comparable complexes (Figure 1 left, Figure S62 and Table S1) [14,21,[33][34][35].Interestingly, the PtL b -n complexes present a stronger absorption band in the 1 MLCT (≈420 nm) region if compared with the PtL a -n complexes.This can be attributed to the higher contribution of the alkoxy group in para position (with respect to the Pt atom) to the HOMO than in case of the moiety in meta position, and therefore to a higher destabilization of the HOMO (as previously observed for Ir(III) complexes and [36,37] in phenylpyridine Pt(II)-based complexes [38]).
The emission spectra of the PtL a -n complexes (Figure 1 right, Figure S63) show a maximum at 517 nm with vibrational shoulders at 553 nm, which arise mainly from 3 MP-LC states [14,33,34,39].The spectra of PtL b -n are red-shifted with a maximum at 555 nm (Figure 1 right, Figure S64).The red shift in the emission can be also ascribed to a destabilization of the HOMO and consequently to a reduction in the gap between the excited and ground state [37,38].To support and interpret the experimental results, (TD-)DFT calculations were performed for the methoxy-substituted complexes (PtL a -1 and PtL b -1) as model compounds.After the geometry optimization of the ground state (S0) and the lowest triplet state (T1) was achieved, the emission maxima were calculated (Figure S77) [40][41][42][43][44][45][46][47].The emission spectra of the PtL a -n complexes (Figure 1 right, Figure S63) show a maximum at 517 nm with vibrational shoulders at 553 nm, which arise mainly from 3 MP-LC states [14,33,34,39].The spectra of PtL b -n are red-shifted with a maximum at 555 nm (Figure 1 right, Figure S64).The red shift in the emission can be also ascribed to a destabilization of the HOMO and consequently to a reduction in the gap between the excited and ground state [37,38].To support and interpret the experimental results, (TD-)DFT calculations were performed for the methoxy-substituted complexes (PtL a -1 and PtL b -1) as model compounds.After the geometry optimization of the ground state (S 0 ) and the lowest triplet state (T 1 ) was achieved, the emission maxima were calculated (Figure S77) [40][41][42][43][44][45][46][47].
A detailed characterization of the emissive state can be achieved with the aid of a correlated electron-hole pair analysis using the software package for Theoretical Density, Orbital Relaxation and Exciton analysis (TheoDORE) [48].The result of the decomposition into contributions from MLCT, LMCT (ligand-to-metal charge transfer), LC and MC is presented in Figure 2. The higher MLCT character in the excited state of PtL b -n, particularly if compared with PtL a -n (25.0%vs 21.1%, respectively), may be responsible for the lack of vibronic progression in PtL b -n complexes, due the stronger geometrical distortion in the excited state.The distortion of the excited state (∆Q) can be estimated by the so-called Huang-Rhys factor (S) according to Equation ( 1), where I 0-0 is the emission intensity of the 0-0 transition and I 1-0 the one corresponding to the first vibronic peak (Table 1) [26].Consistently, S is higher for PtL b -n than for PtL a -n complexes.The photophysical properties were also studied in diluted glassy matrices of 2-methyltetrahydrofuran (complex concentration, c ≈ 10 −5 M) at 77 K.All the complexes show a blue shift in the emission spectra of approximately 10 nm, if compared with the solutions at r.t.This is a consequence of the weaker charge-transfer stabilization associated with the limited solvent reorientation in the rigid matrices, thereby decreasing the 3 MLCT character of the emissive state [49,50].Another consequence of the restricted solvent reorientation is the reduced density of solvent-related roto-vibrational states, thus leading to a welldefined vibrational progression [51].Interestingly, the reduction in S is more significant for PtL b -n than for PtL a -n when the fluid solution is changed to the glassy matrix, which is in agreement with a higher loss of MLCT character from the lack of solvent reorientation.The excited state of Pt(II) complexes can be deactivated in fluid solution by 3 O2-mediated diffusional quenching, which is reflected in the decrease (by a factor > 50) in the knr  The photophysical properties were also studied in diluted glassy matrices of 2-methyltetrahydrofuran (complex concentration, c ≈ 10 −5 M) at 77 K.All the complexes show a blue shift in the emission spectra of approximately 10 nm, if compared with the solutions at r.t.This is a consequence of the weaker charge-transfer stabilization associated with the limited solvent reorientation in the rigid matrices, thereby decreasing the 3 MLCT character of the emissive state [49,50].Another consequence of the restricted solvent reorientation is the reduced density of solvent-related roto-vibrational states, thus leading to a well-defined vibrational progression [51].Interestingly, the reduction in S is more significant for PtL b -n than for PtL a -n when the fluid solution is changed to the glassy matrix, which is in agreement with a higher loss of MLCT character from the lack of solvent reorientation.
The excited state of Pt(II) complexes can be deactivated in fluid solution by 3 O 2mediated diffusional quenching, which is reflected in the decrease (by a factor > 50) in the k nr after Ar purging of the samples.The PtL a -n series shows longer lifetimes (Figures S65-S76) and higher quantum yields than their PtL b -n isomers (Table 2); a similar effect was previously reported for Ir(III) complexes [37].
When the complexes are studied in dilute fluid solutions, different conformations are thermally accessible and possess comparable excited state characters yet different deactivation rates; therefore, multiexponential decays can be observed in some cases.This effect is also noticeable in glassy matrices, yielding multiexponential decays as previously reported for other Pt(II) complexes [33,51,52].Compared to the analogous complex with a methoxyphenyl group (which has been previously reported by our group [4]), PL a -6 presents somewhat higher k r and k nr rates.This can be attributed to the reduced steric strain associated with the n-alkyl substitution, as opposed to a phenyl moiety at the bridging N-atom.The k r and k nr values of PtL a -n and PtL b -n show two interesting trends.The k r are in the same range for both luminophores; however, PtL b -n complexes present k nr values between 2 and 3 times higher than the PtL a -n compounds.In this case, the faster nonradiative intersystem crossing rate constant between the T 1 and S 0 states can be ascribed to the higher geometrical distortion in the excited state of PtL b -n, if compared with the PtL a -n complexes.It would be expected that a lower MLCT character of the excited state leads to a higher k r at 77 K than at r.t.However, the four complexes show a counterintuitive tendency, with higher k r at lower temperatures.This was already observed for other Pt(II) complexes with tridentate luminophores, and (TD-)DFT calculations at a higher level of sophistication (including a temperature-dependent Boltzmann analysis of the radiative rate constants) will be needed to elucidate the nature of this observation [53].    [.d Average radiationless deactivation rate constant [54].e Monoexponential decay.f Biexponential decay.

Thermochromic Properties
The thermochromic properties of the compounds were studied by differential scanning calorimetry (DSC), polarized optic microscopy (POM) and temperature-dependent steadystate luminescence spectroscopy.
In DSC experiments (Table 3, Figures S78-S81), PtL a -6 melts at 245 • C with decomposition.No changes below this temperature were observed in POM.PtL a -12 shows, within a first cycle, a crystal-to-crystal transition at 74 • C, while melting at 197 • C and crystallizing again at 186 • C (Figure S82).Changes in the melting temperature within cycles for PtL a -12 indicate a small decomposition during the phase transition.PtL b -6 and PtL b -12 both melt at around 130 • C, returning not to a crystalline phase, but rather to a glassy phase in a reversible way (Figures S83 and S84).In the case of the "open" series PtL b -n, the increasing chain length produces an enhancement of the van der Waals interactions between the alkyl groups while causing a slight raise of the melting temperature and a significant increment of the melting enthalpy.
Interestingly, the transitions undergone by PtL a -12 involve a change in the luminescence colour, with a decrease of the monomeric emission and the growth of an unstructured yet red-shifted band.This new luminescence can be ascribed to the formation of dimers and aggregates where the Pt•••Pt distances are shorter than 3.5 Å. [3,14,34,55].The assignment of this emission band was carried out by comparing the calculated emission spectra of the dimers with the experimental bands measured upon heating of the samples.The calculated emission spectra of PtL a -1 and PtL b -1 dimers are in very good agreement with the experimental data (Figure 3).Interestingly, the transitions undergone by PtL a -12 involve a change in the luminescence colour, with a decrease of the monomeric emission and the growth of an unstructured yet red-shifted band.This new luminescence can be ascribed to the formation of dimers and aggregates where the Pt•••Pt distances are shorter than 3.5 Å. [3,14,34,55].The assignment of this emission band was carried out by comparing the calculated emission spectra of the dimers with the experimental bands measured upon heating of the samples.The calculated emission spectra of PtL a -1 and PtL b -1 dimers are in very good agreement with the experimental data (Figure 3).Powder X-ray diffractometry of PtL a -12 was performed before and after heating the sample above the transition temperature.The diffraction pattern before the thermal treatment shows typical Bragg reflections of a polycrystalline sample.Upon heating, no Bragg reflections are observed while showing the formation of a mostly amorphous solid (Figure 4).
In the case of complexes PtL b -6 and PtL b -12, the monomeric emission intensities decrease with increasing temperature (Figures S86 and S87), as expected for the progressive population of roto-vibrational states while leading to faster non-radiative deactivation rates.On the other hand, PtL a -12 shows a very stable emission intensity at 512 nm as a function of temperature below the transition temperature.In the range between 65 °C and 75 °C, the emission intensity at 512 nm decreases by roughly 80%.
The emission spectra of PtL a -12, PtL b -6 and PtL b -12 were measured 48 h after melting (Figure 5).Notably, each complex exhibits a different behaviour.PtL a -12 keeps the emission of the aggregates kinetically blocked and PtL b -6 shows partial recovery, whereas for PtL b -12 the original emission (i.e., before heating) is fully recovered.These observations can be explained in terms of the intermolecular interactions within the solids: the "closed" complexes PtL a -n possess a higher dipolar moment than the "open" PtL b -n series.Consequently, the interaction between the aromatic cores within the aggregates is more pronounced.Conversely, the longer alkyl moieties disrupt the interactions between the aromatic planes [56,57].As a result of these combined effects, PtL b -12 is able to return to a Powder X-ray diffractometry of PtL a -12 was performed before and after heating the sample above the transition temperature.The diffraction pattern before the thermal treatment shows typical Bragg reflections of a polycrystalline sample.Upon heating, no Bragg reflections are observed while showing the formation of a mostly amorphous solid (Figure 4).
In the case of complexes PtL b -6 and PtL b -12, the monomeric emission intensities decrease with increasing temperature (Figures S86 and S87), as expected for the progressive population of roto-vibrational states while leading to faster non-radiative deactivation rates.On the other hand, PtL a -12 shows a very stable emission intensity at 512 nm as a function of temperature below the transition temperature.In the range between 65 • C and 75 • C, the emission intensity at 512 nm decreases by roughly 80%.
The emission spectra of PtL a -12, PtL b -6 and PtL b -12 were measured 48 h after melting (Figure 5).Notably, each complex exhibits a different behaviour.PtL a -12 keeps the emission of the aggregates kinetically blocked and PtL b -6 shows partial recovery, whereas for PtL b -12 the original emission (i.e., before heating) is fully recovered.These observations can be explained in terms of the intermolecular interactions within the solids: the "closed" complexes PtL a -n possess a higher dipolar moment than the "open" PtL b -n series.Consequently, the interaction between the aromatic cores within the aggregates is more pronounced.Conversely, the longer alkyl moieties disrupt the interactions between the aromatic planes [56,57].As a result of these combined effects, PtL b -12 is able to return to a monomer-dominated phase, whereas PtL b -6 achieves only a partial reversion.Ultimately, the more robust dipole interactions sustain the aggregates in the case of PtL a -12.
monomer-dominated phase, whereas PtL b -6 achieves only a partial reversion.Ultimately, the more robust dipole interactions sustain the aggregates in the case of PtL a -12.

Conclusions
Four new Pt(II) complexes with CˆN*NˆC ligands were synthesized and characterized.The position of the alkoxy groups has a crucial effect on the photophysical properties of the monomeric complexes by varying the metal participation on the excited state.The PtL b -n complexes with an extended metal contribution display emission maxima that are red-shifted by approximately 45 nm while having higher k nr values in comparison with their PtL a -n isomers; this demonstrates that small changes in the ligand structure can significantly affect the photophysical properties.The alkyl chain length affects the capability of the complexes to form crystalline phases and their transition temperatures.Interestingly, the phase transitions facilitate the Pt-Pt coupling, which causes a red-shifted luminescence due to the formation of dimers.Depending on the substitution pattern and the alkyl chain length, the thermal properties of the materials can be tuned.Moreover, the balance between the different classes of intermolecular interactions affects the memory of thermal exposure above the transition temperatures.Hence, variable alkyl chain lengths can be exploited to design materials with different sensitivity ranges, in order to cover appropriated windows for their use as sensors with multiple optical readouts (i.e., based on photoluminescence wavelengths, intensities and lifetimes).

Figure 2 .
Figure 2. Molecular orbitals dominating the T1 state of PtL a -1 and PtL b -1 at the optimized T1 geometry (left).Characterization of the emissive T1 state by correlated electron-hole pair analysis (right).

Figure 2 .
Figure 2. Molecular orbitals dominating the T 1 state of PtL a -1 and PtL b -1 at the optimized T 1 geometry (left).Characterization of the emissive T 1 state by correlated electron-hole pair analysis (right).

Figure 3 .
Figure 3. Molecular orbitals dominating the description of the T1 state for the dimers of PtL a -1 A (left) and PtL b -1 B (right) at the optimized T1 geometry (left).Calculated (solid lines) and experimental (dashed lines) emission spectra of the aggregates (right).

Figure 3 .
Figure 3. Molecular orbitals dominating the description of the T 1 state for the dimers of PtL a -1 A (left) and PtL b -1 B (right) at the optimized T 1 geometry (left).Calculated (solid lines) and experimental (dashed lines) emission spectra of the aggregates (right).

Figure 4 .
Figure 4. (a) Emission spectra of solid PtL a -12 upon heating (λexc = 470 nm).(b) Emission intensity at 512 nm and 661 nm as a function of the temperature.(c) X-ray diffraction pattern of PtL a -12 before and after the phase transition.Inset: detail of the X-ray diffraction pattern after the phase transition.(d) Photographs of solid PtL a -12 at different temperatures under UV-light excitation, λexc = 365 nm.

Figure 5 .
Figure 5. Emission spectra of PtL a -12 (red), PtL b -12 (green) and PtL b -6 (orange) after melting and 48 h storage under ambient conditions (left).Photographs of the complexes PtL a -12 (A), PtL b -12 (B) and PtL b -6 (C) after melting and 48 h storage under ambient conditions as observed under room light and under UV-light irradiation, λexc = 365 nm (right).

Figure 4 .
Figure 4. (a) Emission spectra of solid PtL a -12 upon heating (λ exc = 470 nm).(b) Emission intensity at 512 nm and 661 nm as a function of the temperature.(c) X-ray diffraction pattern of PtL a -12 before and after the phase transition.Inset: detail of the X-ray diffraction pattern after the phase transition.(d) Photographs of solid PtL a -12 at different temperatures under UV-light excitation, λ exc = 365 nm.

Figure 4 .
Figure 4. (a) Emission spectra of solid PtL a -12 upon heating (λexc = 470 nm).(b) Emission intensity at 512 nm and 661 nm as a function of the temperature.(c) X-ray diffraction pattern of PtL a -12 before and after the phase transition.Inset: detail of the X-ray diffraction pattern after the phase transition.(d) Photographs of solid PtL a -12 at different temperatures under UV-light excitation, λexc = 365 nm.

Figure 5 .
Figure 5. Emission spectra of PtL a -12 (red), PtL b -12 (green) and PtL b -6 (orange) after melting and 48 h storage under ambient conditions (left).Photographs of the complexes PtL a -12 (A), PtL b -12 (B) and PtL b -6 (C) after melting and 48 h storage under ambient conditions as observed under room light and under UV-light irradiation, λexc = 365 nm (right).

Figure 5 .
Figure 5. Emission spectra of PtL a -12 (red), PtL b -12 (green) and PtL b -6 (orange) after melting and 48 h storage under ambient conditions (left).Photographs of the complexes PtL a -12 (A), PtL b -12 (B) and PtL b -6 (C) after melting and 48 h storage under ambient conditions as observed under room light and under UV-light irradiation, λ exc = 365 nm (right).
FigureS76.Left: Raw time-resolved photoluminescence decay of PtL b -12 (c ≈ 10 −5 M) in a frozen glassy matrix of 2Me-THF at 77 K, including the residuals (λ exc = 376.7 nm, λ em = 540 nm).Right: Fitting parameters including pre-exponential factors and confidence limits.FigureS77.Calculated emission spectra at 77 K in THF.FigureS78.DSC profile of PtL a -6 on heating with a heating/cooling rate of 10 • C/min.First cycle (black and red curves), second cycle (blue and green curves), third cycle (purple and brown curves).FigureS79.DSC profile of PtL a -12 on heating with a heating/cooling rate of 10 • C/min.First cycle (black and red curves), second cycle (blue and green curves), third cycle (purple and brown curves).
Figure S80.DSC profile of PtL b -6 on heating with a heating/cooling rate of 10 • C/min.First cycle (black and red curves), second cycle (blue and green curves), third cycle (purple and brown curves).
Figure S81.DSC profile of PtL b -12 on heating with a heating/cooling rate of 10 • C/min.First cycle (black and red curves), second cycle (blue and green curves), third cycle (purple and brown curves).
Figure S82.POM images of PtL a -12 in the crystalline phase (left) and in the isotropic phase (right) after melting on cooling.Figure S83.POM images of PtL b -6 in the glassy phase (left) and in the isotropic phase (right) after melting on cooling.Figure S84.POM images of PtL b -12 in the glassy phase (left) and in the isotropic phase (right) after melting on cooling.Figure S85.Left: Emission spectra of solid PtL a -12 upon heating (λ exc = 470 nm).Centre: Emission intensity at 512 nm and 661 nm as a function of the temperature.Right: Photographs of solid PtL a -12 at different temperatures under UV excitation, λ exc = 365 nm.

Figure S86 .
Figure S86.Left: Emission spectra of solid PtL b -6 upon heating (λ exc = 470 nm).Centre: Emission intensity at 512 nm and 661 nm as a function of the temperature.Right: Photographs of solid PtL a -12 at different temperatures under UV excitation, λ exc = 365 nm. Figure S87.Left: Emission spectra of solid PtL b -12 upon heating (λ exc = 470 nm).Centre: Emission intensity at 512 nm and 661 nm as a function of the temperature.Right: Photographs of solid PtL a -12 at different temperatures under UV excitation, λ exc = 365 nm.

Table 1 .
Huang-Rhys factor in fluid solution at r.t. and in glassy matrices at 77 K for the four complexes.

Table 1 .
Huang-Rhys factor in fluid solution at r.t. and in glassy matrices at 77 K for the four complexes.

Table 2 .
Photophysical parameters of the complexes.

Table 3 .
Transition temperatures and enthalpies of the complexes.
Temperatures given in • C; enthalpies in kJ•mol −1 are indicated in parentheses.Cr: crystalline phase; I: isotropic liquid.Heating rates: 10 • C/s.Values are reported in the second heating cycle except for PL a -6.

Table 3 .
Transition temperatures and enthalpies of the complexes.Temperatures given in °C; enthalpies in kJ•mol −1 are indicated in parentheses.Cr: crystalline phase; I: isotropic liquid.Heating rates: 10 °C/s.Values are reported in the second heating cycle except for PL a -6.