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Paper
Org. Biomol. Chem., 2009, 7, 3222 - 3229, DOI: 10.1039/b905945h
Planar chiral asymmetric naphthalenediimide cyclophanes: synthesis, characterization and tunable FRET properties
Sandro Gabutti, Silvia Schaffner, Markus Neuburger, Matthias Fischer, Gabriel Schäfer and Marcel Mayor
A series of planar chiral asymmetric naphthalenediimide (NDI) cyclophanes ( 1–4) consisting of two different NDIs interlinked by rigid meta-dimethylenebenzene spacers was synthesized. A modular synthetic strategy based on the dichloro cyclophane 1 as common precursor gave a straightforward access to racemic mixtures of the NDI cyclophane dyes 2–4. In particular the substitution of both chlorine atoms of 1 by tert-butylsulfanyl-, methoxy- and piperidinyl-groups provided racemic mixtures of the fluorescent NDI cyclophane dyes 2, 3 and 4 respectively. Fluorescence spectroscopy revealed chemically tuneable intramolecular FRET properties, as the spectral overlap between the emission of the unsubstituted NDI and the absorption of the core-substituted NDI subunit of the cyclophane could be adjusted by the core substituents. The racemic nature of the samples of cyclophanes 2–4, and in the case of the di-tert-butylsulfanyl functionalized cyclophane 2 the enrichment of both enantiomers, was demonstrated by HPLC using a chiral stationary phase. The solid state structure of 2 was determined by X-ray analysis. A periodic arrangement of both enantiomers of the planar chiral cyclophane 2 in pillars such that NDI- and 2,6-core substituted NDI chromophores alternate periodically was observed.
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