Investigations of Opto-Electronically Interesting Materials Featuring Phosphorus-Carbon Double Bonds

Molecules and polymers featuring π-conjugation have garnered much attention due to their applications in opto-electronic materials. The electronic properties of organic polymers can be “tuned” by altering the band gap between the HOMO and LUMO through doping, changing the length of conjugation, grafting functional groups and side chains onto the building blocks of the polymers, or incorporating elements that are active participants in the conjugation. The introduction (n-type) or removal (p-type) of electrons into the π-conjugated system of the polymer is critical for the formation of new materials having practical applications as molecular switches, photovoltaics, sensors, and organic light emitting diodes.

Due to the similarities between phosphorus and carbon (based on electronegativity), phosphorus is often referred to as a “carbon copy” and the introduction of phosphorus into carbon-based systems is seen in many examples throughout the literature. Phosphaalkenes are analogous to alkenes and feature a double bond between the phosphorus and carbon atoms. Phosphaalkenes, of the form 4-R-2,6-Mes₂C₆H₂P=C(H)C6H4-4-R' (where R = H or MeO and R′ = H or CN), with potential use in nonlinear optical materials, were studied using cyclic voltammetry to determine the effects of electron-withdrawing and electron-donating substituents on the reduction potential.

Incorporation of phosphorus into the main chain of an oligomeric or polymeric material has met some challenges because of the lack of stability in air, due to the reactive P=C bond, and the lack of planarity, due to steric hindrance, which causes a loss in the π-conjugation between the P=C π-system and aromatic π-system of the phenyl ring. The next step in designing compounds which overcome these issues was by incorporating the P=C unit into a ring structure, thus preventing rotation and loss of conjugation. Heterophospholes, specifically 1,3-benzoxaphospholes and benzobisoxaphospholes, present such an option for study. In this report, detailed efforts to synthesize, characterize, and determine the redox behavior of these two systems has been investigated.