Platinum polyynes

These new complexes and polymers are related to the square-planar palladium and platinum polyynes which have recently been shown (25-28) to exhibit interesting X ) behavior. We have not yet measured the %(3) properties of our rhodium complexes, or the molecular weights of the polymers. Current synthetic work is directed towards understanding the influence of the linker groups on electronic communication between the metal centers, and on designing new linkers with low-lying 7i levels to improve conjugation. 

FIGURE 17. Transparency region for selected platinum polyynes and some benchmark optical limiters (Cu-Pc-tBu4=CuII-tetrakis(tert-butyl)phthalocyanine Zn-TPP=ZnII-tetrakis(4-phenyl)porphyrin). 

Soluble platinum polyynes containing bithiazole units in the backbone were prepared by Wong et al.71 Polymer 22 was prepared via dehydrohalogenation reactions and contains... 

The synthesis of several high molecular-weight platinum polyyne polymers carrying chiral (R)-l,l -bi-2-naphthol bridge, P17, was described.48 These represent the first examples of metal acetylide polymer with an optically active backbone. They display much larger specific negative optical rotations than both the metal-free alkyne precursors and their corresponding dinuclear model compounds. These results support the fact that the main chain of P17 adopts a one-handed helical conformation and induces the helical chirality of the polymers. 

Raithby and co-workers further compared the photophysical properties of several platinum(II) polyynes P25, P27, and P29 with their organic copolyynes.59 Since the nonradiative decay rate for the triplet emission, (Lm)p, is equal or larger than the corresponding radiative decay rate, (Ljjp, the PL quantum efficiencies of the platinum polyynes are reduced from those for the organic polymers. Optical data reveal that the anchoring of octyl side chains on the fluorenyl spacer reduces interchain interaction in the polyynes, while a fluorenonyl spacer affords a donor-acceptor motif along the rodlike backbone. 

Figure 6.6 Space-filling diagram for the model compound of the platinum polyyne P49.

Figure 6.8 Optical band gaps (Eg in eV) for platinum polyynes with different spacer groups R.

The synthesis of platinum polyynes with heteroaromatic organic spacer groups has also been readily accomplished, for example, species 188 with skeletal pyridyl units that make use of the dehydrohalogenation method (Scheme 16(a)) or an McsSnCl elimination procedure analogous to that in Equation (64) (Scheme 17)." The resultant polymers could be quaternized at nitrogen with methyl iodide and triflate. Materials such as 189 with a bithiazole spacer have also been prepared by the dehydrohalogenation method. 

A step-growth polycondensation route has been succesfully devised to prepare novel nickel polymers 207 with arene spacer groups. The procedure involved the polycondensation of the fluorinated dilithiated species 206 and an Ni(ii) complex (Equation (75))." " The rod-like structure of these polymers was established by dilute-solution viscosity measurements, and the results were similar to those reported for the related platinum polyyne polymers 166 (M = Pt(P Bu3)2 x = 2) (Section 12.06.5.2.3). 

The absolute moleeular weights of these materials have been established by GPG by means of the universal calibration technique that involves the acquisition of intrinsic viscosity data. As with the aforementioned platinum polyyne polymers 166 (M = Pt(P"Bu3)2 x = Z), the intrinsic viscosities were found to be independent of the nature of the solvent and a Mark-Houwink a-value of 1.5 was determined, which is indicative of a rodlike structure. Interestingly, it was found that in this case, GPG, using PS standards, underestimates the true molecular weight of the polymers. This was attributed to the high molar mass of a repeat unit in the Ni polymer 207 compared to PS, which overcompensates for the effect of the rigid-rod structure that would be expected to lead to the opposite situation. Absolute values of of up to ca. 1 x 10 were determined for the polymer samples. 

Platinum polyynes represent one of the most interesting and well-studied classes of linear metallopolymers. Dendritic analogs of these materials have been prepared via a variety of methodologies. One example is the nonametallic dendrimer 248 that was prepared via a convergent route as illustrated in Equation (92). Dendrimers based on ruthenium polyyne architectures have also been prepared and promising NLO properties have been identified. ... 

Fig. 5.5 Photocells constructed from single layers of platinum polyynes 5.32 and 5.33.

Although rigid-rod polyynes are still being investigated some of their properties in general and those of the platinum polyynes in particular are beginning to be unraveled. These can be summarized as follows ... 

Scheme 7 shows the polycondensation of the diethynyl monomer 79 with the dichloroplatimun complex 80. In this example, the polymerization reaction occurs at the metal center to )deld the platinum polyyne 81. ... 

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