Exclusion complexes of γ-cyclodextrin with conjugation-extended viologens displaying photochromic and fluorescent properties in solid-state

The search for multifunctional molecular materials continues to be one of the most exciting research topics due to their broad range of applications. Herein, we report two multifunctional supramolecular host−guest exclusion complexes, formed through exo-binding of γ-CD with two conjugation-extended viologen guests, namely, N,N′-di(3-carboxy-propyl)-4,4′-(1,4-phenylene)-bipyridinium dichloride (PV·Cl₂) and N,N′-di(3-carboxy-propyl)-4,4′-(1,4-naphthalene)-bipyridinium dichloride (NV·Cl₂). The exclusion complexes PV²⁺∩γ-CD₂ and NV²⁺∩γ-CD₂ exhibited photochromic behavior and photomodulable fluorescence simultaneously in the solid-state. In particular, NV²⁺∩γ-CD₂ showed fluorescence activity under both 365 nm and 430 nm light excitation. Benefiting from their concurrent dual readout signals, the exclusion complexes can be applied to multiple anti-counterfeiting as well as multi-level information encryption. This study provides a host−guest exo-binding strategy for constructing multifunctional molecular materials.