Tuning the Aggregation of N^{^}N^{^}C Pt(II) Complexes by Varying the Aliphatic Side Chain and Auxiliary Halide Ligand: ¹H and ¹⁹⁵Pt NMR Investigation

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. Experimental data allowed to predict the most probable geometry of the dimers and to get insight into the structural and thermodynamic specificity of the aggregation. The in‐depth analysis of the data suggests that the halide auxiliary ligand has no significant influence on self‐association while the effect of the aliphatic side chain depends on the length and the structure of the chain.

Enhancing Circularly Polarized Phosphorescence via Integrated Top‐Down and Bottom‐Up Approach

“…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.…”

“…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.…”

On the thermodynamics of aggregation toward phosphorescent metallomesogens: From electronic tuning to supramolecular design

“…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.…”

“…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 $$5d_{z^2}$$ 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).…”

Unusual Reactivity and Photophysical Properties of Platinum(II) Pincer Complexes Containing 6,6'‐Diphenyl‐2,2'‐bipyridine Ligands

“…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,…”