We report a strategic synthesis of poly(cyclosilane), a well-defined polymer inspired by crystalline silicon. The synthetic strategy relies on the design of a functionalized cyclohexasilane monomer for transition-metal-promoted dehydrocoupling polymerization. Our approach takes advantage of the dual function of the phenylsilyl group, which serves a crucial role both in the synthesis of a novel α,ω-oligosilanyl dianion and as a latent electrophile. We show that the cyclohexasilane monomer prefers a chair conformation. The monomer design ensures enhanced reactivity in transition-metal-promoted dehydrocoupling polymerization relative to secondary silanes, such as methylphenylsilane. Comprehensive NMR spectroscopy yields a detailed picture of the polymer end-group structure and microstructure. Poly(cyclosilane) has red-shifted optical absorbance relative to the monomer. We synthesize a σ-π hybrid donor-acceptor polymer by catalytic hydrosilylation.

The flexibility of σ-conjugated silanes presents new opportunities for manipulating charge generation, transport, and non-linear optical properties of materials. Recently we synthesized a series of acceptor-donor-acceptor (ADA) compounds in which a methylated oligosilane core (D) is flanked by electron-deficient cyanovinyl-substituted arenes (A). Based on a detailed characterization of the photophysics of ADA and donor-acceptor (DA) architectures using both steady state and ultrafast spectroscopic measurements we illustrate that asymmetric charge separation occurs directly following light absorption. Lippert analysis of solvatochromic emission indicates large changes in dipole moments on excitation consistent with the formation of dipolar emissive states. Time resolved absorption measurements reveal common excited-state relaxation behavior across molecular structures: spectral dynamics associated with the relaxation of nascent excited states occur on a common timescale for all structures within the same solvent environment, whereas charge recombination via excited-state decay consistently follows a common energy gap law. Ultrafast time-resolved Raman measurements reveal that reduction of the cyanovinyl moieties is instantaneous with excitation, with only minor shifts in vibrational features over the course of excited-state relaxation. We conclude that excited-state symmetry breaking that gives rise to asymmetric intramolecular charge transfer (ICT) is associated with the conformation of the central Si chain. In contrast, ultrafast solvent reorganization or solvent-controlled intramolecular dynamics only serve to stabilize nascent dipolar excited states, rather than induce charge separation from an initial quadrupolar state.

A class of hybrid oligosilane–arene materials outperforms the σ- and π-conjugated parent structures.

We show that ultrasound-induced mechanical force isomerizes an azobenzene centered within a poly(methyl acrylate) polymer from cis to trans configuration without cleaving the azo bond. The isomerization rate was not altered by the polarity of the solvent indicating that the isomerization occurs through a non-polar, inversion transition state.