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Three new pharmaceutical co-crystals: 1 PZA-MA (malonic acid), 2 PZA-SA (succinic acid, a new polymorph of a reported one), and 3 PZA-GA (glutaric acid) have been prepared and characterized by differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), and single-crystal X-ray diffraction. Wherein, PZA formed 1:1 co-crystals with MA and GA by acid–amide and acid–py heterosynthon, while it formed 2:1 co-crystal with SA by amide–amide homosynthon in addition to acid–amide and acid–py heterosynthon. Their melting points follow the order, PZA-GA < PZA-MA < PZA-SA, which are lower than the melting points of the individual components. Hirshfeld surface analysis revealed that N–H···O hydrogen bonding and π···π interactions for PZA in them follow the order: PZA-MA > PZA-SA > PZA-GA, while H–H and O–O interactions follow the order: PZA-MA < PZA-SA < PZA-GA. We also compared the Hirshfeld surfaces of the present co-crystals with the nine reported PZA co-crystals, which obtained important results. The studies of the solubility and dissolution showed a semiempirical inverse relationship with the melting point: the solubility follows the order, PZA-SA < PZA-GA < PZA-MA and dissolution rate follows the order, PZA-SA < PZA-MA < PZA-GA.

Numerous emerging applications require precise monitoring of humidity that is not only sensitive and miniaturized but also durable and portable. However, except for the existing sensing mechanisms, such as resistive, capacitive, impedance, and voltage-based devices, little attention has been paid to exploiting dual readout modes with novel properties that can meet the requirements of simplicity and convenience. In this work, an example of color/fluorescence dual-switching by using an aggregator building block of naphthalenediimide with a porous hygroscopic polymer matrix is proposed. With an increase in the water fraction, there are obvious variations in fluorescence, driven by H-aggregation of the aggregator, and in color, driven by intramolecular-charge transfer, which facilitate the monitoring of external humidity. More importantly, the prepared humidity-sensitive switch demonstrated excellent cycling stability and reversibility. This work may shed light on the precise fabrication of aggregation-activated materials for potential applications in humidity-sensitive systems and switching devices.