Fingerprints of Through-Bond and Through-Space Exciton and Charge π-Electron Delocalization in Linearly Extended [2.2]Paracyclophanes

Abstract

New stilbenoid and thiophenic compounds terminally functionalized with donor-donor, acceptor-acceptor, or donor-acceptor moieties and possessing a central [2.2]paracyclophane unit have been prepared, and their properties interpreted in terms of through-bond and through space π-electron delocalization (i.e., π-conjugations). Based on photophysical data, their excited-state properties have been described with a focus on the participation of the central [2.2]paracyclophane in competition with through-bond conjugation in the side arms. To this end, two-photon and one-photon absorption and emission spectroscopy, as a function of temperature, solvent polarity, and pressure in the solid state have been recorded. Furthermore, charge delocalization through the [2.2]paracyclophane in the neutral state and in the oxidized species (radical cations, dications and radical trications) has been investigated, allowing the elucidation of the vibrational Raman fingerprint of through-space charge delocalization. Thus, a complementary approach to both "intermolecular" excitation and charge delocalizations in [2.2]paracyclophane molecules is shown which can serve as models of charge and exciton migration in organic semiconductors.

Large Conductance Variations in a Mechanosensitive Single-Molecule Junction

“… 24 The molecular motif and substitution pattern allow for flexibility by stretching of the PC; the ethynylphenylthiol building block, however, only offers limited movement upon application of a pulling force on the molecule ( Figure 1 c). High-pressure solid state absorption experiments on PC derivatives show shortened distances between 25 When the thiol groups are moved apart, the applied tensile force is relayed to the central PC unit along the axis connecting the anchoring groups ( Figure S4 ). Our DFT calculations show that the alkynes are more susceptible to compressive motions, whereas the PC subunit only stretches after these are fully extended.…”

A highly substituted pyrazinophane generated from a quinoidal system via a cascade reaction

“…2,[7][8][9]17 Additionally, [2.2]paracyclophanes have been of recent interest to the organic electronics research community as models of intramolecular charge transfer. [18][19][20][21] The p-AQM family of molecules contain quinoidal nitrogen-substituted rings that are structurally homologous to the p-AQM mentioned earlier (Scheme 1c). 12,17 The synthesis of p-AQMs produces compounds with directly conjugated aromatic and quinoidal units, yielding low band-gap organic semiconductors with varied structures.…”

Beyond Simple Substitution Patterns – Symmetrically Tetrasubstituted [2.2]Paracyclophanes as 3D Functional Materials

“…Cram and Reich were further able to elucidate the chemistry of PC, where they found remarkable transannular effects and unique behavior, for example in thermal isomerization of substituted isomers and in directing effects, which can dominate the direction of the electrophilic aromatic substitution on PC derivatives . Nowadays, the focus has shifted away from the chemical modification of PC and its application in asymmetric catalysis, and materials chemistry is now in the foreground . The extraordinary configuration of the molecule displays a face‐to‐face arrangement of a two slightly‐bent aromatic rings, with short inter‐ring distances between 2.83 and 3.09 Å.…”