Strong Intermolecular Electronic Coupling of Chromophores Confined in Hydrogen-Bonded Frameworks

Guanidinium organodisulfonate (GDS)
hydrogen-bonded frameworks
constructed from “tetris-shaped” ortho-substituted disulfonated
stilbene derivatives display crystal architectures in which the stilbenes
serve as pillars that connect opposing guanidinium sulfonate (GS)
sheets in a continuously layered architecture while guiding the organization
of the stilbene residues into packing motifs that produce unique optical
properties. The constraints imposed by ortho-substitution result in
a heretofore unreported topology of the pillars projecting from the
two-dimensional GS sheet, while the dense packing of stilbene constituents,
confined between the GS sheets, results in strong intermolecular electronic
coupling. Stilbene 420 (2,2″-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)­bis-benzenesulfonate)
pillars pack in a face-to-face brickwork motif, producing a large
bathochromic shift (∼100 nm) of the absorbance and emission
spectra relative to stilbene 420 in methanol. The distyrylbenzenedisufonate
(2,2′-((1E,1′E)-1,4-phenylenebis­(ethene-2,1-diyl))­dibenzenesulfonate)
pillars, which pack in a face-to-face herringbone motif between the
GS sheets, afford both hypsochromic and bathochromic shifts in their
absorption spectrum, indicative of an unusually large Davydov splitting.
The observation of both bathochromic and hypsochromic shifts can be
attributed to the herringbone arrangement, in which both transitions
are allowed due to the nonzero vector sum of the transition dipoles
in both states. The large magnitude of the Davydov splitting reflects
the strong intermolecular coupling between the chromophores, enforced
by confinement in the GS framework. The newly discovered GS architectures
evoke a new design rule that permits prediction of GS topologies in
the case of longer tetris-shaped pillars.