Abstract:A series of six tridentate cyclometallated N^N^C Pt(II) complexes with different halide auxiliary ligands and different aliphatic side chains have been prepared. All complexes show concentration‐dependent NMR spectra. Their self‐association was studied by a dilution method monitoring both the 1H as well as 195Pt nuclei. Both techniques show similar results validating that 195Pt NMR is an important methodology to study self‐association of potentially any Pt complex regardless of the nature of the ligands. Exper… Show more
“…195 Pt{ 1 H} NMR (107 MHz) spectra indicate a downfield shift from −3144.0562 ppm for a 5.0 mM [PtN]ClO 4 solution (CD 2 Cl 2 ) to −3139.4412 ppm for the co‐assemblies of PtN:L‐BT (CD 3 CN) (SI, Figure S6). The shift is ascribed to charge delocalization due to the 5 d z 2 (Pt)⋅⋅⋅5 d z 2 (Pt) interaction along coaxial stacks [93–94] . Taken together, the results reveal that the helical assemblies consist of tightly packed bundles of coaxial molecular wires, wherein [PtN] + planes are aligned in an edge‐on orientation with respect to the substrate.…”
Section: Resultsmentioning
confidence: 81%
“…The shift is ascribed to charge delocalization due to the 5d z 2 (Pt)•••5d z 2 (Pt) interaction along coaxial stacks. [93][94] Taken together, the results reveal that the helical assemblies consist of tightly packed bundles of coaxial molecular wires, wherein [PtN] + planes are aligned in an edge-on orientation with respect to the substrate.…”
In the dynamic domain of chiroptical technologies, it is imperative to engineer emitters endowed with circularly polarized luminescence (CPL) properties. This research demonstrates an advancement by employing a combined top‐down and bottom‐up strategy for the simultaneous amplification of photoluminescence quantum yield (Φ) and the luminescence dissymmetry factor (glum). Square‐planar Pt(II) complexes form helical assemblies, driven by torsional strain induced by bis(nonyl) chains. Integration of chiral anions leads these assemblies to prefer distinct helical sense. This arrangement activates the metal‐metal‐to‐ligand charge transfer (MMLCT) transition that is CPL‐active, with Φ and |glum| observing an upswing contingent on the charge number and aryl substituents in chiral anions. Utilizing the soft‐lithographic micromolding in capillaries technique, we could fabricate exquisitely‐ordered, one‐dimensional co‐assemblies to achieve the metrics to Φ of 0.32 and |glum| of 0.13. Finally, our spectroscopic research elucidates the underlying mechanism for the dual amplification, making a significant stride in the advancement of CPL‐active emitters.
“…195 Pt{ 1 H} NMR (107 MHz) spectra indicate a downfield shift from −3144.0562 ppm for a 5.0 mM [PtN]ClO 4 solution (CD 2 Cl 2 ) to −3139.4412 ppm for the co‐assemblies of PtN:L‐BT (CD 3 CN) (SI, Figure S6). The shift is ascribed to charge delocalization due to the 5 d z 2 (Pt)⋅⋅⋅5 d z 2 (Pt) interaction along coaxial stacks [93–94] . Taken together, the results reveal that the helical assemblies consist of tightly packed bundles of coaxial molecular wires, wherein [PtN] + planes are aligned in an edge‐on orientation with respect to the substrate.…”
Section: Resultsmentioning
confidence: 81%
“…The shift is ascribed to charge delocalization due to the 5d z 2 (Pt)•••5d z 2 (Pt) interaction along coaxial stacks. [93][94] Taken together, the results reveal that the helical assemblies consist of tightly packed bundles of coaxial molecular wires, wherein [PtN] + planes are aligned in an edge-on orientation with respect to the substrate.…”
In the dynamic domain of chiroptical technologies, it is imperative to engineer emitters endowed with circularly polarized luminescence (CPL) properties. This research demonstrates an advancement by employing a combined top‐down and bottom‐up strategy for the simultaneous amplification of photoluminescence quantum yield (Φ) and the luminescence dissymmetry factor (glum). Square‐planar Pt(II) complexes form helical assemblies, driven by torsional strain induced by bis(nonyl) chains. Integration of chiral anions leads these assemblies to prefer distinct helical sense. This arrangement activates the metal‐metal‐to‐ligand charge transfer (MMLCT) transition that is CPL‐active, with Φ and |glum| observing an upswing contingent on the charge number and aryl substituents in chiral anions. Utilizing the soft‐lithographic micromolding in capillaries technique, we could fabricate exquisitely‐ordered, one‐dimensional co‐assemblies to achieve the metrics to Φ of 0.32 and |glum| of 0.13. Finally, our spectroscopic research elucidates the underlying mechanism for the dual amplification, making a significant stride in the advancement of CPL‐active emitters.
“…This robust method involves measurements of samples at variable concentrations and different temperatures while monitoring the chemical shifts of selected key atom probes affected by stacking. [10,[17][18][19] In this work, two new series of asymmetric tetradentate ligand precursors (L Ph -n and L Fpy -n) were synthesized, along with their corresponding Pt(II) complexes having two different cyclometallating rings; within each of the series, three different alkyl chain lengths were probed. The synthesis of asymmetric CˆN*NˆC-coordinated yet non-mesogenic Pt(II) complexes was recently reported by Tunik et al, but without studying the effect of fluorination and chain length on the thermodynamics of aggregation while using orthogonal phenyl moieties at the bridging N-atom.…”
Section: Introductionmentioning
confidence: 99%
“…This phenomenon is mainly driven by van der Waals interactions, but dipolar coupling phenomena and hydrogen bonds also play a role. [ 9,10 ] 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 among the orbital lobes protruding out of the coordination plane becomes feasible. The resulting aggregates show a red‐shifted emission compared to the monomeric species, which arises from triplet metal‐metal‐to‐ligands charge‐transfer ( 3 MMLCT) states with a certain degree of excimeric character (i.e., the interaction is stronger in the excited state than in the ground‐state of the monomers, thus resulting in shortened Pt‐Pt distances).…”
Two series with three Pt(II) complexes each (PtLPh‐n, PtLFpy‐n) bearing asymmetric tetradentate ligands as dianionic luminophores with variable alkyl chain lengths were synthesized. Hence, each ligand series is distinguished by one of its cyclometallating rings (phenyl vs. 2,6‐difluoropyrid‐3‐yl). Steady‐state and time‐resolved photoluminescence spectroscopic studies in diluted solutions at room temperature and in glassy matrices at 77 K show that the emissive state is mainly centered on the invariantly electron‐rich cyclometalated side while the second ring regulates the admixture of ligand‐centered and metal‐to‐ligand charge‐transfer character. Hence, the radiative rates can be controlled, as indicated by quantum‐mechanical calculations, which also explain the temperature‐dependent trend in the phosphorescence rate constants. Studies in condensed phases (single‐crystal X‐ray diffractometry, polarized optical microscopy, differential scanning calorimetry, steady‐state and time‐resolved photoluminescence micro(spectro)scopy) showed the development of a smectic A mesophase for the fluorinated species bearing the two longest alkyl chains. Nuclear magnetic resonance‐based studies on the thermodynamics of aggregation in solution confirm the marked enthalpic stabilization of aggregates mediated by the polar 2,6‐difluoropyrid‐3‐yl moiety (and to a lesser extent by dispersive forces between the alkyl chains). On the other hand, the negative entropy of aggregation is dominated by the restriction of degrees of freedom involving the peripheral alkyl moieties upon stacking, which becomes increasingly relevant for longer chains. All these factors control Pt···Pt coupling, a crucial interaction for the design of photofunctional mesogens based on Pt(II) complexes.
“…Pt(II) complexes containing NNC pincer ligands is a well-known class of luminescent compounds showing outstanding photophysical characteristics, [1][2][3][4][5] which depend on the composition and structure of the NNC aromatic system and on the properties of lateral ligand occupying the fourth coordination position. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] The most part of these compounds are based on the 6-phenyl-2,2′-bipyridine coordinating moiety, [6,7,15,[17][18][19][20][21][22][23] which can be decorated with the substituents at bipyridine and phenyl fragments thus making possible to modify emission parameters of the final chromophores [8][9][10][11][12][13] and their physicochemical properties for various applications. [20,21,23,24] Surprisingly, a closely analogous and easily synthesized 6,6′-diphenyl-2,2′-bipyridine ligand was very rarely used [25,…”
A series of novel 6,6'‐diphenyl‐2,2'‐bipyridine ligands modified with the substituents at phenyl and bipyridine moieties have been prepared and used in the synthesis of pincer platinum chloride complexes 1–3, [Pt(NNC–R)Cl], where NNC–R – dimethyl 6,6'‐diphenyl‐[2,2'‐bipyridine]‐5,5'‐dicarboxylate (R = H, (1)), dimethyl 6,6'‐bis(4‐fluorophenyl)‐[2,2'‐bipyridine]‐5,5'‐dicarboxylate (R = F (2)), dimethyl 6,6'‐bis(4‐methoxyphenyl)‐[2,2'‐bipyridine]‐5,5'‐dicarboxylate (R = OMe (3)). Reactions of the obtained compounds with triphenylphosphine proceed through unusual pathway, which gives the [Pt(NNC–R)(PPh3)2Cl] products (1a–3a) containing two phosphine ligands, with the chloride retained in coordination sphere and diphenyl‐bipyridine fragment coordinated in η1‐mode through metalation of a pyridine ring. All complexes have been characterized with mass‐spectrometry and NMR spectroscopy, solid‐state structure of 1–3 and 1a, 3a was revealed by using XRD crystallography. The complexes 1–3 are phosphorescent in dichloromethane solution and in solid state. Their photophysical characteristics were determined and analyzed by DFT calculations, which gave assignment of emissive excited state character with the major contribution from the intraligand charge transfer (3ILCT, Ph→bipyridine) and ligand centered (3LC, bipyridine fragment) transitions.
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