Copolymers and homopolymers containing silicon atoms connected to three and four other silicon atoms have been prepared and characterized. We report the first evidence of dendritic polymers with silicon backbones. Copolymers made from RSiCl3 and R1R2SiCl2 resemble hybrid materials of polysilyne and polysilanes. Polymers, which contain tetrasilyl‐substituted Si atoms, [(SiMe2)4Si]n and (Si)m(Me2Si)n, have also been synthesized. These molecules appear to be the first hyperbranched polymers, which have applications based on their electronic properties. The properties of these molecules fit into the hierarchy of 1‐D to 3‐D topologies known for Si materials.
Two new π* indicators of solvent dipolarity and polarizability were synthesized and characterized with respect to their solvatochromic and acid‐base properties. The new dyes, N,N‐dipropyl‐p‐nitroaniline and N,N‐dibutyl‐p‐nitroaniline, are part of a homologous structural series of indicators with increasing lipophilic character, ranging from N,N‐dimethyl‐p‐nitroaniline to N,N‐dibutyl‐p‐nitroaniline. The new indicators are designed as specific polarity probes for the characterization of aqueous‐organic interfacial systems. Visible absorption spectra for N,N‐dipropyl‐p‐nitroaniline and N,N‐dibutyl‐p‐nitroaniline show solvent‐dependent bandshapes in a manner similar to that of the previously characterized diethyl species. Values of ‐s decrease slightly from N,N‐diethyl‐p‐nitroaniline to N,N‐dipropyl‐p‐nitroaniline, leveling off with increasing alkyl chain length. The trend in pK BH + for the p‐nitroanilinium ions over the range from N,N‐dimethyl‐ to N,N‐dibutyl‐ is consistent with known trends for the corresponding anilinium ions. © 1997 John Wiley & Sons, Ltd.
An investigation of the UV absorption and emission properties of n-Si16Me34 in room-and low-temperature solutions revealed a striking similarity to the photophysical behavior of high molecular weight peralkylated poly silanes. The absorption is that expected for a statistical collection of chromophoric segments. Room-temperature emission is that expected from the lowest excitation energy conformations of approximately 16-silicon chains, presumably all-trans. Their excited states are believed to be generated by energy transfer in the polymer and by adiabatic conformational transformations in the hexadecasilane. The latter process is suppressed in 3-methylpentane glass, where many spectrally distinct conformers are observed to behave independently. Three of them dominate and have been characterized spectrally. At concentrations of 5 X 6 M and higher, 3-methylpentane solutions of Si16Me34 formed dimeric or oligomeric species upon fast cooling and precipitated a microcrystalline solid upon slow cooling. These, too, have been spectrally characterized.
Solvent-sensitive probes have wide application in the study and characterization of interfacial systems. This work presents some new, more hydrophobic versions of the solvatochromic π* indicators of solvent dipolarity−polarizability. The new dyes form a homologous series of N,N-dialkyl-p-nitroanilines. The indicators are designed to act as improved probes of micelles and lipid bilayers in polar and aqueous solutions. UV−vis studies of the N,N-dipentyl- and N,N-dihexyl-p-nitroanilines show the two indicators to be strongly solvatochromic; values of − s estimated from two-point correlation are 3.081and 3.110, respectively. UV−vis spectra of N,N-dipentyl- and N,N-dihexyl-p-nitroanilines obtained at variable indicator concentration in cyclohexane and dimethyl sulfoxide, within the 10-5 M concentration range, display no concentration-dependent spectral shifting and no evidence of indicator aggregation in accordance with Beer's law. Studies of the indicator series in aqueous solutions of varying concentration of the anionic surfactant sodium dodecyl sulfate (SDS) suggest that N,N-dipropyl-p-nitroaniline probes micelles of SDS more deeply than the commonly used N,N-dimethyl- and N,N-diethyl-p-nitroanilines. Of the three indicators in the series, N,N-dimethyl-, N,N-diethyl-, and N,N-dipropyl-p-nitroaniline, the dipropyl species is most responsive to the critical micelle concentration of SDS. The longer chain dyes N,N-dibutyl-, N,N-dipentyl-, and N,N-dihexyl-p-nitroaniline are more effective probes of larger micelles of the nonionic surfactant Triton X-114. UV−vis studies of N,N-dihexyl-p-nitroaniline in micellar solutions of Triton X-114 and model systems suggest that the longest chain indicator probes the outer polyoxyethylene portion of the Triton X-114 micelle.
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