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Published May 2009 | Supplemental Material
Journal Article Open

Rigidity−Stability Relationship in Interlocked Model Complexes Containing Phenylene-Ethynylene-Based Disubstituted Naphthalene and Benzene

Abstract

Structural rigidity has been found to be advantageous for molecules if they are to find applications in functioning molecular devices. In the search for an understanding of the relationship between the rigidity and complex stability in mechanically interlocked compounds, the binding abilities of two π-electron-rich model compounds (2 and 4), where rigidity is introduced in the form of phenylacetylene units, toward the π-electron deficient tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT^(4+)), were investigated. 1,4-Bis(2-(2-methoxyethoxy)ethoxy)-2,5-bis(2-phenylethynyl)benzene 2 and 1,5-bis(2-(2-methoxyethoxy)ethoxy)- 2,6-bis(2-phenylethynyl)naphthalene 4 were synthesized, respectively, from the appropriate precursor dibromides 1 and 3 of benzene and naphthalene carrying two methoxyethoxyethoxy side chains. The rigid nature of the compounds 2 and 4 is reflected in the reduced stabilities of their 1:1 complexes with CBPQT^(4+). Binding constants for both 2 (100 M^(-1)) and 4 (140 M^(-1)) toward CBPQT^(4+) were obtained by isothermal titration microcalorimetry (ITC) in MeCN at 25 °C. Compounds 1-4 were characterized in the solid state by X-ray crystallography. The stabilization within and beyond these molecules is achieved by a combination of intra- and intermolecular [C-H· · · O], [C-H· · ·π], and [π-π] stacking interactions. The diethyleneglycol chains present in compounds 1-4 are folded as a consequence of both intra- and intermolecular hydrogen bonds. The preorganized structures in both precursors 1 and 3 are repeated in both model compounds 2 and 4. In the structures of compounds 2 and 4, the geometry of the rigid backbone is differentsthe two terminal phenyl groups are twisted with respect to the central benzenoid ring in compound 2 and roughly perpendicular to the plane central naphthalene core in compound 4. To understand the significantly decreased stabilities of these complexes toward rigid guest molecules, relative to more flexible systems, we performed density functional theory (DFT) calculations using the newly developed M06-suite of density functionals. We conclude that the reduced binding abilities are a consequence of electronic and not steric factors, originating from the extended delocalization of the aromatic system.

Additional Information

© 2009 American Chemical Society. Received October 3, 2008; Revised Manuscript Received January 6, 2009. Publication Date (Web): March 11, 2009. This work was supported by the Microelectronics Advanced Research Corporation (MARCO) and its Focus Center Research Program (FCRP), the Center on Functional Engineered Nano Architectonics (FENA), and NSF (ECS-0609128). Computational facilities were funded by grants from ARO-DURIP and ONR-DURIP. We thank Dr. Saeed I. Khan for his assistance with a Bruker SMART CCD diffractometer at UCLA. Supporting Information Available: ITC spectra (PDF) and crystallographic information in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

Attached Files

Supplemental Material - Yoon2009p2572Cryst_Growth_Des_supp.pdf

Supplemental Material - cg801106h_si_002.cif

Supplemental Material - cg801106h_si_003.cif

Supplemental Material - cg801106h_si_004.cif

Supplemental Material - cg801106h_si_005.cif

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August 20, 2023
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