Neutral orthometalated platinum(II) complexes of the deprotonated 6-phenyl-2,2'-bipyridine ligand (bearing a trialkoxygallate, tolyl, ethynyltrialkoxygallate, or ethynyltolyl substituent) and a sigma-bonded Cl, ethynyltolyl, or ethynyltrialkoxygallate coligand have been prepared by a stepwise procedure based on copper-promoted cross-coupling reactions. The X-ray structure of the [2-(p-tolyl)ethynyl][4-{2-(p-tolyl)ethynyl}-6-phenyl-2,2'-bipyridyl)]platinum(II) complex revealed a coplanar arrangement of all residues bound to platinum, although the tolylethynyl groups exhibit position-dependent bending in the solid state. The complexes exhibit charge-transfer absorption in the visible region. All except two of the complexes also exhibit charge-transfer emission, typically from an excited state that has a submicrosecond lifetime at room temperature in deoxygenated dichloromethane solution. In accordance with the presence of a carbometalated polypyridine ligand, the emitting state is assumed to have a mixture of metal-to-ligand charge-transfer (MLCT) and intra-ligand charge-transfer (ILCT) character. However, spectral comparisons and electrochemical data suggest that the emissive state also exhibits interligand charge-transfer (LLCT) character when an electron-rich ethynylaryl group is bound to platinum. In keeping with altered orbital parentage in the latter systems, the emission occurs at longer wavelength. The excited-state lifetime is also shorter, evidently due to vibronic interactions. The decay is so efficient when an ethynyltrialkoxygallate group binds to platinum that there is no detectable emission in fluid solution, although the complexes do emit in a frozen glass. The excited states are subject to associative (exciplex) quenching by Lewis bases, but the admixture of ILCT and/or LLCT character diminishes efficiency, except for relatively strong bases like dimethyl sulfoxide and dimethylformamide.

This paper focuses on DNA-binding interactions exhibited by Pt(dma-T)CN(+), where dma-T denotes 4'-dimethylamino-2,2':6',2''-terpyridine, and includes complementary studies of the corresponding pyrr-T complex, where pyrr-T denotes 4'-(N-pyrrolidinyl)-2,2':6',2''-terpyridine. The chromophores are useful for understanding the interesting and rather intricate DNA-binding interactions exhibited by these and related systems. One reason is that the terpyridine ligands employed provide intense visible absorption and enhanced photoluminescence signals. Incorporating cyanide as a coligand further aids analysis by suppressing covalent binding. Physical methods utilized include X-ray crystallography for structures of the individual inorganic complexes. Viscometry as well as spectral studies of the absorbance, emission, and circular dichroism (CD) yield information about interactions with a variety of DNA hosts. Although there is no sign of covalent binding under the conditions used, most hosts exhibit two phases of uptake. Under conditions of high loading (low base-pair-to-platinum ratios), the dma-T complex preferentially binds externally and aggregates on the surface of the host, except for the comparatively rigid host [poly(dG-dC)]2. Characteristic signs of the aggregated form include a bisignate CD signal in the charge-transfer region of the spectrum and strongly bathochromically shifted emission. When excess DNA is present, however, the complex shifts to intercalative binding, preferentially next to G[triple bond]C base pairs if available. Once the complex internalizes into DNA it becomes virtually immune to quenching by O2 or solvent, and the emission lifetime extends to 11 micros when [poly(dI-dC)]2 is the host. On the other hand, the host itself becomes a potent quenching agent when G[triple bond]C base pairs are present because of the reducing strength of guanine residues.

The morphological development of cellular polyimide microstructures from poly(amic acid) powders has been shown to depend on the processing conditions throughout the inflation process and the morphological characteristics of the precursor particles. In an earlier publication the authors presented a numerical study of the preliminary stages prior to particle inflation when the processing temperature is below the glass transition temperature, Tg. In the present article, a second numerical scheme is presented for behavior above Tg in which bubble growth is modeled to account for the effect of multiple phenomena in the final stages of morphological development. The bubble growth kinematics and subsequent cessation of growth are predicted as a function of process parameters and material properties. Morphological characteristics of the precursor particles have also been shown to influence the kinematics of inflation. These results provide a clearer understanding of the solid‐state foaming processes for polyimide cellular materials. POLYM. ENG. SCI., 47:572–581, 2007. © 2007 Society of Plastics Engineers.

Several concurrent phenomena occur during the thermal inflation of poly(amic acid) precursor particles leading to polyimide foams as part of the solid-state powder foaming process. The precursor experiences bubble growth from within while volatiles desorb and the polymer itself increases its molecular weight and changes its backbone structure. These changes affect the transport properties of the material by modifying significantly the effective glass transition temperature, T g . By studying the chemical transformations that take place during the inflation process (amidation and imidization reactions), a complete understanding of the material's molecular changes can be obtained and corresponding property changes can be followed. This article is the third of a series where the inflation of precursor materials for polyimide foams has been studied. The two previous articles in the series present numerical models that simulate the inflation process from first principles. In this article, the authors discuss the experimental and analytical methodologies employed to accurately characterize and incorporate the changes in material and transport properties as a function of the glass transition temperature. POLYM. ENG. SCI.,

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