The growing realization that photoinduced bending of slender photoreactive single crystals is surprisingly common has inspired researchers to control crystal motility for actuation. However, new mechanically responsive crystals are reported at a greater rate than their quantitative photophysical characterization; a quantitative identification of measurable parameters and molecular-scale factors that determine the mechanical response has yet to be established. Herein, a simple mathematical description of the quasi-static and time-dependent photoinduced bending of macroscopic single crystals is provided. This kinetic model goes beyond the approximate treatment of a bending crystal as a simple composite bilayer. It includes alternative pathways for excited-state decay and provides a more accurate description of the bending by accounting for the spatial gradient in the product/reactant ratio. A new crystal form (space group P21/n) of the photoresponsive azo-dye Disperse Red 1 (DR1) is analyzed within the constraints of the aforementioned model. The crystal bending kinetics depends on intrinsic factors (crystal size) and external factors (excitation time, direction, and intensity).

There is rapidly developing interest in the potential of macrocyclic host molecules to modify the effective pK a values of included guests. Following early reports of small pK a shifts of included guests in cyclodextrins (DpK a % 1) [1,2] and cucurbit[6]uril [3] (DpK a % 1), we have used cucurbit [7]uril (CB7, DpK a % 2-3) [4,5] and sulfonatocalixarenes (DpK a % 2) as additional hosts and proposed structure-reactivity relationships.

UV–vis and NMR spectroscopic techniques were employed to demonstrate the ability of the synthetic macrocyclic host cucurbit[7]uril (CB7) to solubilize and stabilize widely used fungicides and anthelmintic drugs of the benzimidazole family in water, namely, albendazole (ABZ), carbendazim (CBZ), thiabendazole (TBZ), fuberidazole (FBZ), and the parent benzimidazole (BZ). CB7 binds the protonated forms of these guests very strongly (e.g., K = 2.6 × 107 L/mol for ABZ) but their neutral forms significantly more weakly (e.g., K = 6.5 × 104 L/mol for ABZ), which reflects a complexation-induced increase of their pKa values by 2.6 units for ABZ, 2.5 units for CBZ, 4.0 units for TBZ, 3.8 units for FBZ, and 3.5 units for BZ. The absolute drug solubilities increased upon complexation from 0.003 to 0.300 mmol/L for ABZ, from 0.160 to 1.12 mmol/L for CBZ, from 0.110 to 1.11 mmol/L for TBZ, and from 0.25 to 0.75 mmol/L for FBZ (for BZ, the solubility enhancement was found to be insignificant). Complexation by CB7 further improves the photostability of the drugs and alters their photophysical properties.

Non-toxic covalent organic nanosheet-based fluorescent nuclear stains.