Stereoelectronic Effects, Mechanism, And Synthesis In Sulfonyl Chemistry

ABSTRACT HAS BEEN ARCHIVED 09/17/93

Structural Characterization of Quaterphenyl Cation Radical: X-ray Crystallographic Evidence of Quinoidal Charge Delocalization in Poly-\u3cem\u3ep\u3c/em\u3e-phenylene Cation Radicals

Quaterphenyl derivative (QP) containing tert-butyl solubilizing groups at the terminal positions yields a stable cation radical salt that was isolated, and its structure was established by X-ray crystallography. The crystal structure of neutral QP and its cation radical (QP+•SbCl6-) provides unequivocal evidence for the quinoidal stabilization of the cationic charge or polaron by smoothing out the torsional motion of the interconnected p-phenylene rings. Such an observation of stabilization of the cationic charge in a poly-p-phenylene (PPP) derivative forms the basis for the noted high conductivities in PPP oligomers in their doped state

Structural Characterization of Quaterphenyl Cation Radical: X-ray Crystallographic Evidence of Quinoidal Charge Delocalization in Poly-\u3cem\u3ep\u3c/em\u3e-phenylene Cation Radicals

Quaterphenyl derivative (QP) containing tert-butyl solubilizing groups at the terminal positions yields a stable cation radical salt that was isolated, and its structure was established by X-ray crystallography. The crystal structure of neutral QP and its cation radical (QP+•SbCl6-) provides unequivocal evidence for the quinoidal stabilization of the cationic charge or polaron by smoothing out the torsional motion of the interconnected p-phenylene rings. Such an observation of stabilization of the cationic charge in a poly-p-phenylene (PPP) derivative forms the basis for the noted high conductivities in PPP oligomers in their doped state

From Static to Dynamic: Electron Density of HOMO at Biaryl Linkage Controls the Mechanism of Hole Delocalization

In order to extend the physical length of hole delocalization in a molecular wire, chromophores of increasing size are often desired. However, the effect of size on the efficacy and mechanism of hole delocalization remains elusive. Here, we employ a model set of biaryls to show that with increasing chromophore size, the mechanism of steady-state hole distribution switches from static delocalization in biaryls with smaller chromophores to dynamic hopping, as exemplified in the largest system, tBuHBC2 (i.e., “superbiphenyl”), which displays a vanishingly small electronic coupling. This important finding is analyzed with the aid of Hückel molecular orbital and Marcus–Hush theories. Our findings will enable the rational design of the novel molecular wires with length-invariant redox/optical properties suitable for long-range charge transfer

Hexabenzo[4.4.4]propellane: A Helical Molecular Platform for the Construction of Electroactive Materials

Helical hexabenzo[4.4.4]propellane (a relative of hexaphenylethane) and its derivatives are synthesized and their structures are established by X-ray crystallography. Isolation and X-ray crystallographic characterization of a robust trication-radical salt of hexamethoxypropellane derivative confirms that its framework is stable toward oxidative (aliphatic) C−C bond cleavage. It is also demonstrated that propellane can be easily brominated at the 4,4‘-positions of the biphenyl linkages for its usage as a molecular platform for the preparation of electroactive materials

A Versatile Synthesis of Electroactive Stilbenoprismands for Effective Binding of Metal Cations

A versatile synthesis of a new class of polyaromatic receptors (stilbenoprismands) containing a Δ-shaped cavity similar to that of the π-prismand together with an intimately coupled electroactive stilbenoid moiety was accomplished via an efficient intramolecular McMurry coupling reaction. The presence of the Δ-shaped cavity in stilbenoprismands allows an efficient binding of a single silver cation as probed by 1H NMR spectroscopy. Electron-rich stilbenoprismands undergo a ready oxidation to their highly robust cation−radical and dicationic salts. X-ray structure determination of a representative dicationic stilbenoprismand showed that the charges were largely localized on the tetraarylethylene moiety, which results in a twisting of the ethylenic C═C bond by ∼35°. Moreover, the electronic coupling among the stilbenoid and π-prismand moieties in various stilbenoprismands was briefly probed by optical methods

Electron Transfer Prompted Ejection of a Tightly Bound K\u3csup\u3e+\u3c/sup\u3e from the Ethereal Cavity of a Hexaarylbenzene-Based Receptor

Synthesis of a pair of rotamers (9u/9s) of a hexaarylbenzene derivative containing six (cofacially arranged) electroactive 2,5-dimethoxytolyl groups is described. The toroidal electronic stabilization due to the circular arrangement of aryl groups in 9u/9s leads to the observation of multiple (reversible) oxidation waves and lowering of their Eox1 by ∼250 mV relative to model compounds. The binding of K+ to symmetrical rotamer 9s was monitored by an electrochemical method and further confirmed by X-ray crystallography

A Polyaromatic Receptor with an Ethereal Fence that Directs K\u3csup\u3e+\u3c/sup\u3e for Effective Cation−π Interaction

We have designed and synthesized a HAB-based receptor with six ethereal oxygens on one face of the central benzene ring by a trimerization of a diarylacetylene in which the ethereal oxygens are tied together with a tetramethylene bridge. This unique amphiphilic receptor allows an efficient binding of a single potassium cation by a synergistic interaction with the polar ethereal fence and with the central benzene ring via cation−π interaction. Furthermore, the ready accessibility of this unique receptor with a bipolar binding pocket will allow the exploration of its usage for developing efficient sensing devices for various metal cations

A Circle Has No End: Role of Cyclic Topology and Accompanying Structural Reorganization on the Hole Distribution in Cyclic and Linear Poly‑p‑phenylene Molecular Wires

π-Conjugated organic oligomers/polymers hold great promise as long-range charge-transfer materials for modern photovoltaic applications. However, a set of criteria for the rational design of functional materials is not yet available, in part because of a lack of understanding of charge distribution in extended π-conjugated systems of different topologies, and concomitant effects on redox and optical properties. Herein we demonstrate the role of cyclic versus linear topology in controlling the redox/optical properties and hole distribution in poly-p-phenylenes (PPs) with the aid of experiment, computation, and our recently developed multistate parabolic model (MPM). It is unequivocally shown that the hole distribution in both cyclic and linear poly-p-phenylene (n ≥ 7) cation radicals is limited to seven p-phenylene units, despite the very different topologies. However, the effect of topology is evidenced in the very different trends in oxidation potentials of cyclic versus linear PPs, which are shown to originate largely from the geometrical distortion of individual p-phenylene units in cyclic PPs. The presence of additional pairwise electronic coupling element in cyclic PPs, absent in linear PPs, plays a significant role only in smaller cyclic PP5 and PP6. This study provides a detailed conceptual description of cyclic and linear poly-p-phenylene cation radicals and demonstrates the versatility and predictive power of MPM, an important new tool for the design and synthesis of novel and efficient charge-transfer materials for molecular electronics and photovoltaic applications, an area of widespread interest

Terphenyl Crowns: a New Family of Receptors Containing Ethereal Canopies that Direct Potassium Cation onto Benzenoid Platforms for Cation–π Interactions

We have synthesized three simple and versatile terphenyl crowns (TC) receptors containing ethereal canopies that direct a potassium cation for efficient cation–π interactions as established by 1H NMR spectroscopy and by isolation and X-ray crystallography of their K+ salts