Relatively efficient photovoltaic devices were fabricated using blends of a phosphorescent platinum-acetylide polymer and a fullerene (PCBM); involvement of the triplet excited state of the platinum-acetylide polymer in photoinduced charge transfer is believed to contribute to the device efficiency.

A series of 4'-tolylterpyridyl platinum(II) complexes with different arylacetylide ligands, namely, phenylacetylide, 4-bromophenylacetylide, 4-nitrophenylacetylide, 4-methoxyphenylacetylide, 4-dimethylaminophenylacetylide, 1-naphthylacetylide, and 3-quinolinylacetylide, were synthesized. Their photophysical properties, such as electronic absorption spectra, emission characteristics at room temperature and 77 K, and transient difference absorption spectra, have been investigated. All of these complexes exhibit a metal-to-ligand charge-transfer (1MLCT) transition at ca. 420-430 nm in their electronic absorption spectra. For ttpy-Ph, ttpy-C6H4Br-4, ttpy-C6H4OCH3-4, ttpy-C6H4N(CH3)2-4, and ttpy-Np, an additional solvatochromic charge-transfer band appears at ca. 460-540 nm. This band is sensitive to the para substituents on the phenylacetylide ligand and is tentatively assigned to a metal- or/and acetylide-to-terpyridyl charge-transfer transition (i.e., a 1MLCT or/and 1LLCT transition). All of the complexes exhibit room-temperature phosphorescence. The emission can be attributed to a 3MLCT state except for ttpy-C6H4NO2-4, for which the emission likely originates from an intraligand 3pi,pi* state involving the nitrophenylacetylide ligand. For ttpy-C6H4OCH3-4, ttpy-C6H4N(CH3)2-4, and ttpy-Np, there probably is more than one low-energy state in close energy proximity, resulting in multiple exponential decays. In addition, the triplet transient absorption difference spectra of ttpy-Ph, ttpy-C6H4Br-4, ttpy-C6H4NO2-4, and ttpy-Quin exhibit moderately intense, broad absorption bands in the visible region and extending into the near-IR region, which likely originate from the same excited state that emits or from a state that is in equilibrium with the emitting state. It appears that the electron-rich arylacetylide ligands, especially 4-methoxyphenylacetylide and 4-dimethylaminophenylacetylide, cause a decrease of the emission efficiency and disappearance of the transient absorption. In contrast, the complexes that exhibit positive absorption bands in the visible spectral region of the triplet transient difference absorption spectra show substantial optical limiting for nanosecond laser pulses at 532 nm.

The fullerene end-capped platinum acetylide donor-acceptor triad Pt(2)ThC(60) was synthesized and characterized by using photophysical methods and photovoltaic device testing. The triad consists of the platinum acetylide oligomer Ph-[triple bond, length as m-dash]-Pt(PBu3)2-[triple bond, length as m-dash]-Th-[triple bond, length as m-dash]-Pt(PBu3)2-[triple bond, length as m-dash]-Ph (Ph=phenyl and Th=2,5-thienyl, stereochemistry at both Pt centers is trans) that contains fulleropyrrolidine moieties on each of the terminal phenylene units. Electrochemistry of the triad reveals relatively low potential oxidation and reduction waves corresponding, respectively, to oxidation of the platinum acetylide and reduction of the fulleropyrrolidine units. Photoluminescence spectroscopy shows that the singlet and triplet states of the platinum acetylide chromophore are strongly quenched in the triad assembly, both in solution at ambient temperature as well as in a low-temperature solvent glass. The excited state quenching arises due to intramolecular photoinduced electron transfer to produce a charge separated state based on charge transfer from the platinum acetylide (donor) to the fulleropyrrolidine (acceptor). Picosecond time resolved absorption spectroscopy confirms that the charge transfer state is produced within 1 ps of photoexcitation, and it decays by charge recombination within 400 ps. Organic photovoltaic devices fabricated using spin-coated films of Pt2ThC60 as the active material operate with modest efficiency, exhibiting a short circuit photocurrent of 0.51 mA cm(-2) and an open circuit voltage of 0.41 V under 100 mW cm(-2)/AM1.5 illumination. The results are discussed in terms of the relationship between the mechanism of photoinduced electron transfer in the triad and the comparatively efficient photovoltaic response exhibited by the material.

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