Discrete π Stack of a Tweezer-Shaped Naphthalenediimide-Anthracene Conjugate.

The design and synthesis of a tweezer-shaped naphthalenediimide (NDI)-anthracene conjugate (2NDI) are reported. In the structure of the closed form (π ⋅⋅⋅π stack) of 2NDI, which was elucidated by single-crystal XRD, the existence of C-H⋅⋅⋅O hydrogen bonding involving the nearest carbonyl oxygen atom of an NDI unit was suggested. The tunability of π ⋅⋅⋅π interactions was studied by means of UV/Vis absorption, fluorescence and NMR spectroscopy and molecular modelling. This revealed that the π ⋅⋅⋅π interactions in 2NDI affect the absorption and emission properties depending on the temperature. Furthermore, in polar solvents, 2NDI prefers the stronger π ⋅⋅⋅π stack, whereas the π ⋅⋅⋅π interaction is diminished in nonpolar solvents. Importantly, the conformational variations of 2NDI can be reversibly switched by variation in temperature, and this suggests potential application for fluorogenic molecular switches upon temperature changes.