Single-electron delocalization in spiroconjugated systems

Novel spiroconjugated compounds capable of exhibiting {dollar}pi{dollar}-electron delocalization in orthogonal planes have been designed and prepared. The interactions between the two identical halves connected by the spiro link in acceptor and donor molecules have been investigated. The fate of the unpaired electron in the radical ions of these compounds, generated by redox chemistry, has been studied by UV/Vis and ESR spectroscopy, and cyclic voltammetry.; The interactions between the subsystems are governed by the symmetry of the interacting frontier orbitals. The extent of these interactions is mainly influenced by the size of the of the orbital coefficients on the four atoms connected to the spiro center. Substituents on the two halves of the molecules affect the size of these coefficients and consequently the extent of spiro interactions.; All the neutral spiroconjugated acceptor molecules investigated (spirobiindantetraones) exhibit delocalization of their frontier {dollar}pi{dollar}-electron density over the entire molecule. The single electron in the spiroconjugated radical anions is delocalized over both halves of the molecule in polar solvent systems. The electron can be localized on one half of the molecule by ion-pairing effects seen in solvent systems of low polarity. The equilibrium between localized and delocalized behavior can be influenced by changes in solvent polarity and temperature.; The investigation of spiroconjugation effects in radical cations of donor systems (spirobiperimidines and spirobifluorenes) reveals that the unpaired electron in these systems tends to be localized on one half of the molecule. Spirointeractions, if present are weak.; This study showed that spiroconjugated molecules can exhibit delocalization of electrons in mutually perpendicular planes. It may be possible to prepare materials capable of long range three-dimensional electronic communication by appropriate assembly of the spiroconjugated molecules. These charge-transfer components, therefore, have potential to serve as building blocks for molecular materials with increased dimensionality.