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Asymmetric charge separation and recombination in symmetrically functionalized σ–π hybrid oligosilanes

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Abstract

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.

Graphical abstract: Asymmetric charge separation and recombination in symmetrically functionalized σ–π hybrid oligosilanes

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Publication details

The article was received on 01 Feb 2017, accepted on 24 Feb 2017 and first published on 24 Feb 2017


Article type: Paper
DOI: 10.1039/C7DT00384F
Citation: Dalton Trans., 2017, Advance Article
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    Asymmetric charge separation and recombination in symmetrically functionalized σ–π hybrid oligosilanes

    J. Zhou, C. P. Folster, S. K. Surampudi, D. Jimenez, R. S. Klausen and A. E. Bragg, Dalton Trans., 2017, Advance Article , DOI: 10.1039/C7DT00384F

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