The one-dimensional inclusion complexes formed by crystallization from a solution containing urea and 1,4-diiodobuta-1,3-diene (DIBD) undergo a photochemical transformation when subjected to ultraviolet or visible irradiation. In order for this photochemical polymerization process to proceed, the terminal carbon-iodine bonds must be broken by photochemical cleavage and the iodine must leave the urea matrix after photodissociation. It has been established that there is an approximate 40% loss of mass over the course of this photopolymerization process, corresponding to complete loss of iodine in the irradiated samples. We used Raman scattering spectroscopy both to characterize the time dependence of the resulting conjugated polyene chain formation and to understand their internal π-electronic behavior. The investigation of the photopolymerization of DIBD/urea compounds reveal the appearance of three new spectral features at 1121, 1293, and 1509 cm-1. Raman spectra of the channel-confined polyenes are nearly identical to those of known polyene species and to spectra of trans-polyacetylene prepared by solution methods. The kinetic evolution of the product polyenes exhibits three distinctive phases. A comprehensive interpretation of each time phase as being due to the formation of longer urea-bound diiodopolyene chains with a high degree of regularity will be presented. Additionally, a quantum chemical simulation of these observations using density functional theory will be discussed.

Raman studies of the photopolymerization of 1,4-diiodobuta-1,3-diene in crystalline urea inclusion compounds

253rd National Meeting (2017)

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