N. Fernández-Labandeira, P. Remón, R. Castellano, M. Touriño-Pardo, M. D. García, U. Pischel, A. Blanco-Gómez, C. Peinador. Org. Chem. Front., 2026
https://doi.org/10.1039/d6qo00793g
Enforced chromophore proximity provides a powerful molecular design principle to reshape excited-state interactions and tune emission. In this work, we report the optical properties of two self-assembled cyclophanes in which the interplanar distance between the longitudinal bispyridinium chromophores is sufficiently short to promote intramolecular interactions. Both cyclophanes were efficiently synthesized through acid-catalyzed hydrazone condensation in water without the need for a templating effect, highlighting their high preorganization for cyclization. Photophysical studies in acetonitrile revealed clear excited-state interchromophoric interactions in both systems. The cyclophane containing the more conjugated bispyridinium unit (o–REx4+) displayed a pronounced red-shifted emission (91 nm) and a nearly ninefold increase in emission efficiency relative to its monomeric counterpart. In contrast, chromophoric interaction in the less conjugated cyclophane (o–R4+) induced fluorescence of an otherwise non-emissive bispyridinium chromophore. The emissions are strongly quenched in water, however, complexation with cucurbit[8]uril (CB[8]) restores the fluorescence of both cyclophanes through the formation of stable ring-in-ring host–guest complexes. These results highlight an efficient synthetic approach to highly preorganized cyclophanes and demonstrate how solvent effects and CB[8] complexation can be exploited to modulate and recover the fluorescence of intramolecular chromophore dimers.
