Jason R. Cox

Synthesis, Reactivity, and Electronic Properties of 6,6-Dicyanofulvenes

A series of 6,6-dicyanofulvene derivatives are synthesized starting from masked, dimeric, or monomeric cyclopentadienones. The reactivities of 6,6-dicyanofulvenes relative to their parent cyclopentadienones are discussed. 6,6-Dicyanofulvenes are capable of undergoing two consecutive, reversible, one-electron reductions and are presented as potential n-type small molecules.

Interrupted energy transfer: highly selective detection of cyclic ketones in the vapor phase.

We detail our efforts toward the selective detection of cyclic ketones, e.g. cyclohexanone, a component of plasticized explosives. Thin films comprised of a conjugated polymer are used to amplify the emission of an emissive receptor via energy transfer. We propose that the energy transfer is dominated by an electron-exchange mechanism to an upper excited state of the fluorophore followed by relaxation and emission to account for the efficient energy transfer in the absence of appreciable spectral overlap. Exposure to cyclic ketones results in a ratiometric fluorescence response. The thin films show orthogonal responses when exposed to cyclic ketones versus acyclic ketones. We demonstrate that the exquisite selectivity is the result of a subtle balance between receptor design and the partition coefficient of molecules into the polymer matrix.

Photoalignment Layers for Liquid Crystals from the Di-π-methane Rearrangement

Photoalignment of nematic liquid crystals is demonstrated using a di-π-methane rearrangement of a designed polymer. The alignment mechanism makes use of the strong coupling of the liquid crystal directors to dibenzobarrelene groups. The large structural changes that accompany photoisomerization effectively passivate segments of the polymer, allowing the remaining dibenzobarrelene groups to dominate the director alignment. Photoisomerization requires triplet sensitization, and the polymer was designed to have a uniaxially fixed rigid structure and rapid triplet energy transfer from the proximate benzophenone units to the dibenzobarrelene groups. The isomerization was observed to be regiospecific, and thin films showed alignment.