Design, syntheses, and study of electron communication through conformationally-adaptable and cofacially arrayed polybenzenoid structures; "Search of new molecular motifs for molecular wires"
Abstract
Intermolecular noncovalent binding of silver cations by synthetic macromolecular receptors continues to attract considerable attention. Importantly, the focus has been to design molecular systems that bear two or more aromatic groups in cofacially-oriented arrays (such as cis -diarylalkenes, cyclophanes, triptycenes, deltaphanes, cylinderophanes, etc.) as electron donors for the preparation of metal ion-aromatic donor-acceptor complexes for the potential applications in area of electrical conductors and photoresponsive devices. Despite numerous ingenious designs of novel receptors, including the ones containing fluorescent sensing units, need remains for a readily-available and versatile receptor that can bind silver cations effectively and should allow its eventual incorporation into a polymeric backbone for practical applications in the emerging area of molecular electronic and nanotechnology. We have thus designed and synthesized a versatile fluorene-based receptor Z1 , which adapts a deltaphane-like conformer via a simple C-C bond rotation. Such a conformational adaptability allows the receptor to bind a single silver cation with remarkable efficiency (K ∼ 15,000 M-1 ) as monitored by 1 H NMR or UV-vis spectroscopy. From this inspiration we have prepared fluorene p -xylene oligomers that undergo ready folding into structures that contain multiple deltaphane-like receptor sites in the presence of silver cations and each cavity accommodates a single silver cation with efficiency equivalent to that of Z1 as gauged by 1 H NMR spectroscopic titrations with Ag+ . We have also designed and synthesized a polymeric-supported material where receptor Z1 was woven onto the backbone of polystyrene. This polymeric-supported receptor binds quantitatively a single silver cation per receptor site with remarkable efficiency that exceed the binding abilities of the well-known tris [2.2.2]-p-cyclophane by at least a factor of 100 as monitored by 1 H NMR spectroscopy. We have also designed and synthesized a hexarylbenzene-based multidentate silver receptor (HH ) constructed from the core of hexaphenylbenzene (HPB ), capable of effectively binding up to 3 equiv. of Ag + (K ∼ 33,000 M-1 ) as monitored by 1 H NMR and UV-vis Spectroscopy. The 1:3 stoichiometry of the complexation [HH , 3 Ag+ ] was confirmed by a Job's plot analysis as well as by a competition experiments with tris [2.2.2]paracyclophane (or deltaphane 2 )--a well known receptor for silver cation.
This paper has been withdrawn.