Air-stable poly(3,3,3-trifluoropropylsilyne) homo- and copolymers

Abstract

A soluble Si-Si bonded polymer (polysilyne, SNP) bearing n-butyl groups (BSNP) has been reported to exhibit a green photoluminescence (PL) at 540 nm (2.30 eV). However, BSNP gradually changed to a colorless solid because of auto-oxidation within a few weeks when the polymer was stored in the absence of light without special care. Herein, we demonstrate the photophysical properties of SNP carrying 3,3,3-trifluoropropyl (TFP) side groups (FSNP), which remains unaffected by autooxidation. This stability against oxidation may be possibly attributable to intra-and inter-molecular CF-Si interactions between the electron-donating Si-Si main chain and the electron withdrawing TFP side groups. FSNP in polar tetrahydrofuran (THF) exhibited an almost pure-blue PL peak at 450 nm (2.76 eV), whereas in non-polar n-octane, it emitted a near-UV peak at 337 nm (3.68 eV), possibly, because of the CF-Si interactions. Additionally, thin films of FSNP exposed to air and in THF exhibited excellent resistance to air oxidation for at least one month, as determined by the lack of any changes in its PL, IR, and Raman spectra. From Gaussian03 calculations (TD-DFT, 6-31G* basis set, B3LYP) of trans-perhydrosiladecaline partially substituted with TFP and n-butyl groups as models of FSNP and BSNP, the most essential roles of TFP groups suggested that (i) the lowest Sis-Sis* transition state becomes the allowed transition by introducing strong polarity to the SNP skeleton and (ii) both the HOMO and LUMO energy levels are significantly stabilized, which provides the observed stability toward air oxidation. The air stability was effective in copolymers carrying TFP and n-butyl groups (FBSNP). However, FSNP and FBSNP that had been pyrolysed at temperatures greater than 500 C exhibited no such air stability because of the loss of the TFP groups.

Preparation and Photocurrent Generation of Silicon Nanosheets with Aromatic Substituents on the Surface

“…Silicon catenation with high dimensions is also of interest. However, a bottom-up process analogous to the preparation of linear polysilanes, such as reduction of organotrichlorosilanes, provided not two-dimensional polysilynes having a regular sheetlike structure but three-dimensional randomly branched polymers. − An exception is the synthesis of ladder polysilanes by well-designed reactions of 1,1,2,2-tetrachlorodisilanes . The top-down process is a candidate for the production of highly organized and well-defined two-dimensional organosilicon sheets having many kinds of substituents.…”