Medium Effect on the Geometric Isomerism of a Centrosymmetrically Disubstituted Naphthalene Derivative with Flexible Methoxytriethylene Glycol Chains

The geometric isomeric diversity of a centrosymmetrically disubstituted naphthalene derivative with flexible methoxytriethyleneglycol chains has been investigated both in the liquid and the solid state. Owing to the fact that the exocyclic C-Aryl-O linking appears to be essentially a double bond, the material can exist in discrete geometric isomers. Variable temperature ultraviolet absorption and fluorescence spectroscopy combined with single crystal X-ray diffraction reveal the nature of the various stereoisomers present in the liquid and solid phase. Computational support is also given wherever possible. In solution, the material exists predominantly as a mixture of two rapidly interconverting stereoisomers; namely, the thermodynamically preferred cis, cis and the energetically closest lying cis, trans configuration. In the solid state, optical spectroscopic methods provide evidence for the presence of a small amount of the energetically highly unstable trans, trans stereoisomer, kinetically trapped in the lattice defined by the scaffold of the predominant cis, cis isomeric form. Unlocking of the seemingly frozen cis, cis trans, trans equilibrium was observed in the molten state.