Spacers platinum polymers

Whether chelation (as opposed to covalent bonding) of an active moiety to an excipient qualifies the entire construct as a new chemical entity (NCE) is a moot point. A case in point is polymer platinate. This compound consists of a polymer backbone, hydroxypropylmethacrylamide, linked to a polypeptide spacer. The peptide is in turn linked with an aminomalonate chelating group, which chelates the platinum compound (Fig. 2). 

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. 

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. 

Most polymetallaynes have band gaps of ca. 2.4-3.2 eV but the value can be reduced substantially to ca. 1.7 eV by the use of alternating donor (bis(phosphine)platinum acetylide) and acceptor (electron-deficient thienopyrazine) units in the backbone as in polymer 191." Similarly, donor-acceptor interactions appear to be important in polymer 192, which possesses a ferrocenylfluorenyl spacer that has a band gap of 2.1 eV. In the absence of the donor metallocene group, the analogous polymer has a substantially wider gap ( g = 2.9... 

Electrochemical studies of several polymetallaynes have also been reported. Reduction of organic spacer groups can be achieved and the oxidation of substituents (e.g., ferrocene) can be reversible. However, electrochemical oxidation of the platinum centers in polymetallaynes appears to occur in two irreversible redox steps (presumably involving Pt VPt and Pt VPt couples). This observation suggests that the chemical doping experiments that were used to increase the electrical conductivities of the polymers described above are not simple processes. 

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). 

Detailed studies have been performed on the photophysics of a range of Pt poly-ynes [68, 75-77], and the energy-gap law for triplet states in a series of platinum poly-ynes has been established [78]. Convincing evidence for Jt-conjugation between metal sites in the main chain has been provided by some of the experiments [75]. The photophysics of polymers with fluorene and carbazole spacers has also been investigated in depth, and the studies indicate that the singlet state extends over more than one repeat unit whereas the triplet state is strongly localized [79]. 

As an example, the PT matrix (spacer -(CH2)20CH2-and Ar phenyl) generated by electrodeposition on platinum or on a glassy carbon plate (area = 5 cm ) at constant potential (-1-1.40 V versus 0.1 M Ag+/Ag reference electrode in acetonitrile, anodic charge = 2 C) was found to afford an interfacial functionalization of 2 pmol cm . Moreover, a direct functional group accessibUity can be electrochemically measured with further complete polymer (PT) recycling by using electroactive probes [98]. 

Two-photcMi absorptimi and ultiafast dynamics of spin photoexcitations have been used for the characterizatimi of cmijugated polymers containing platinum atoms (Scheme 10.8). These complexes show a record intersystem crossing time of 1 ps (with one phenyl spacer) and 6 ps (with three phenyl spacers). This tunable ultrafast intersystem crossing determines the intensity ratio of the phosphorescence and fluorescence emissimi bands and is potentially useful for apphcatimis for white OLEDs [32]. 

Scheme 10.17. Luminescent platinum-containing alkynyl polymers with different aromatic spacers.

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