Exploiting coordination geometry to tune the dimensions and processability of metallosupramolecular polymers†

Achieving precise control over the morphology, dimensions and processability of functional materials is a key but challenging requirement for the fabrication of smart devices. To address this issue, we herein compare the self-assembly behavior of two new Pt(ii) complexes that differ in the molecular and coordination geometry through implementation of either a monodentate (pyridine) or bidentate (bipyridine) ligand. The molecular preorganization of the bipyridine-based complex enables effective self-assembly in solution involving Pt⋯Pt interactions, while preserving aggregate solubility. On the other hand, increased steric effects of the linear bispyridine-based complex hinder an effective preorganization leading to poorly solvated aggregates when a critical concentration is exceeded.

analyzer, integrating sphere and employing U6039-05 PLQY measurement software (Hamamatsu Photonics, Ltd., Shizuoka, Japan). All samples were measured in Suprasil® quartz cuvettes with septa. Deaerated samples were measured upon flushing with argon for 20 min (using the septa with a cannula).
X-ray diffractometric analysis: Powder X-ray diffraction experiments were conducted on a ®Rigaku Smartlab X-ray diffractometer in parallel beam geometry with Cu-Kα radiation. The measurement steps were 0.01 deg with a measurement time per step of 0.6 s, using a voltage of 45 kV and a current of 190 mA. Samples have been prepared by stepwise dropcasting a solution with a concentration of 7.5 mM (MCH) onto a glass microscope plate from FisherbrandTM with a thickness of 0.8-1 mm.

Scanning Electron Microscopy:
The SEM images were recorded on a Phenom Pharos Desktop SEM and on a Phenom ProX Desktop SEM manufactured by Thermo Fisher Scientific. The individual images have been recorded using a zoom between 22500x and 300x with either a BSD or SED detector and an acceleration voltage of either 5 or 10 kV (For individual images please see the corresponding figure caption). All solutions have been dropcasted onto a silicon wafer (10 µL) and additionally coated with Pt using a physical vapor deposition for a time interval of 30 seconds prior to measurement. Scheme S1: Synthesis of complex 1.

Synthesis and Characterization
Compound 3 was synthesized according to procedures previously reported by our group. 1,2 Synthesis of 4 4 was synthesized according to a previously reported method. 3    Synthesis of 1 6 (40 mg, 0.037 mmol, 1.0 eq.) and PtCl 2 (PhCN) 2 (17 mg, 0.037 mmol, 1.0 eq.) were dissolved in distilled toluene (5 mL) under Argon and stirred at 100 °C for 7 days. The solvent was removed in vacuo and the crude product was purified by column chromatography (SiO 2 , DCM) to give an orange powder.

Additional Spectroscopic Data
Scheme S3: Schematic representation of the self-assembly of a structurally related bipyridine based Pt II complex with a larger aromatic OPE system. 2 Our previous report was the first study 2 detailing the influence of coordination geometry on self-assembly. Accordingly, more examples based on a modified molecular design are necessary to understand the structure-property relationship in detail. Hence, we designed the molecules 1 and 2 in our current submission, which exhibit a smaller aromatic moiety and in turn a lower aggregation tendency. V-shaped 1 in our previous example exhibited pathway complexity in a two-step cooperative self-assembly process into a single aggregate (solvated fiber structures). We expected the change in intermolecular interactions in our design to alter this behavior, as the steric demand of the bulky metal center and the flexible solubilizing chains are now balanced against weaker aggregation-inducing interactions. Consequently, we anticipated the system to engage in a different self-assembly behavior to balance the now weaker aggregation inducing interactions by following new aggregation pathways or forming altered molecular arrangements, changing the overall morphology.  In order to confirm the assignment of the low energy absorption band in MCH at high temperature, the absorption maximum was plotted against the solvent polarity in a number of solvents ( Figure S9 + S10). A linear fit of the maximum absorbance against the solvent polarity conducted for 1 (at 298 K) is nearly parallel to that of previously reported Pt(bipy)Cl 2 6 with an offset corresponding to the shift in absorbance observed in the molecularly dissolved state in chloroform. Additionally, we recorded UV/Vis spectra at elevated temperatures revealing a temperature-dependent shift of the absorption maximum for all solvents. As the molecularly dissolved state in MCH cannot be recorded at 298 K due to aggregation, a comparison of the data recorded at elevated temperatures is more appropriate. Unfortunately, most organic solvents have a boiling point well below that of MCH (which is also the reason why it is frequently used in aggregation studies), one exception being toluene. In toluene, the absorbance at 363 K shifts to 454 nm (from 449 nm at room temperature), which indicates that a similar behavior would also be observed for MCH. Taking all these points into consideration, we conclude that the low energy absorbance should be assigned to MLCT transitions.           Based on the supporting evidence from VT-UV/Vis and solvent dependent NMR, we infer that the observed loss of fine structure upon increase of solvent polarity is caused by an increased stabilization of various rotamers in the OPE backbone as well as the pyridine-Pt bond, which has been previously demonstrated for purely organic OPE based molecules. 8 The band centered around 375 nm in MCH is attributed to the transition into an MLCT state of the molecularly dissolved species in analogy to the assignment for 1.        ROESY NMR studies of Agg1 reveal numerous intermolecular close contacts. In particular, the alpha proton H a of the pyridine moiety shows a correlation signal with the proton H d of the peripheral phenyl ring. In addition, a correlation signal with the first methylene unit of the alkyl chain can also be observed. This interaction is highly unlikely to originate from a parallel 1D stack, or from an intramolecular interaction. Hence, this cross-signal hints at a possible interdigitation of more than one stack in the assembly. Furthermore, the proton H b gives a correlation signal with the proton H d as well, although a clear differentiation between inter and intramolecular interactions cannot be made. Various cross-signals between the alkyl chains and the aromatic protons are also appreciable (black boxes). The signals are especially pronounced in the case of the peripheral phenyl ring, possibly through intramolecular close contacts. However, cross-signals with the aromatic protons of the bipyridine moiety can also be observed, indicating an antiparallel arrangement as well as possible interdigitation of the alkyl chains between neighboring stacks. It can also be noted that proton H c exhibits only relatively weak interactions with the alkyl chains, indicating a shielding effect due to the relative positioning inside of the aromatic backbone.  Note that the greyed-out molecules correspond to the layer below the normal colored molecules, while additional layers have been omitted for clarity.         Comparing this pattern with single crystal X-ray structures of structurally related bispyridyldichlorido Pt(II) complexes, 10 we tentatively assign the reflex corresponding to a distance of 3.73 Å to the intermolecular distance between the aromatic moieties. Additionally, the reflex at 2Θ = 23.86°, correlating to a distance of 4.46 Å, can by assigned to the intermolecular distance between the Pt atoms. Additionally, based on the out-of-plane arrangement of the chlorido ligands (torsional angle = 49°) 10 two separate reflexes corresponding to the intrastrand Pt-Cl distances can be observed ( Figure S36). The shorter distance (Pt1-Cl22 / Pt2-Cl11) can be observed at 4.34 Å, while for the second intermolecular Pt-Cl distance (Pt1-Cl21 / Pt2-Cl12) a reflex at 2Θ = 16.29° corresponding to 5.47 Å can be appreciated. In accordance with the single crystal analysis of the structurally related reference compound 10 reflexes corresponding to distances of 6.51, 7.54 and 12.08 Å are attributed to interstrand Pt-Pt distances.