Novel Molecular Weight and Solvatochromisms in Poly(methyl-3,3,3-trifluoropropylsilane) Induced by Cooperative Through-Space Si···F−C Interactions

Abstract

Novel helical poly(methyl-3,3,3-trifluoropropylsilane) (1) has been synthesized via Wurtz coupling by taking advantage of noncovalent Si···F−C intramolecular interactions. Such weak Si···F−C interactions make the conformation of the polysilane unique and controllable by proper choice of solvent and molecular weight. We have studied the conformation of polysilane by means of UV absorption, photoluminescence, NMR spectra, and viscosity measurements. Polysilane displayed a 73 helical rodlike conformation in noncoordinating solvents (e.g., toluene and decane) but a globule-like conformation in coordinating solvents (with N, O, or F as donor) at room temperature. The coordinating nature of solvents played an important role for solvatochromic transition rather than the solvent polarity, as such interactions are competitive in the presence of solvents with donor atoms. On the other hand, an analogous nonfluorinated polysilane, poly(n-propylmethylsilane) (2), revealed a disordered conformation in coordinating as ...