7,9(11)-trien-3β-ol (9,11-dehydroprovitamin D 3 , CTL) is used as a fluorescent probe to track the presence and migration of cholesterol in vivo. CTL is known to be photochemically active, but little consideration has been given to the formation efficiency and possible toxicity of its photoproducts. In degassed tetrahydrofuran (THF) solution, we isolated the photoproduct of CTL and of its 25-hydroxy derivative (HOCTL), and X-ray crystal structures were obtained for HOCTL and the photorearrangement product. The X-ray crystal structure and its 1 H NMR spectrum confirm the product structure as a pentacyclic HOCTL isomer. In the presence of air in THF, endoperoxide formation via [2+4] addition of 1 O 2 * across the B ring of CTL or HOCTL becomes the dominant photoreaction. The UV spectrum and decay kinetics of the triplet state of HOCTL, the precursor of 1 O 2 *, are determined by transient absorption spectroscopy. We confirm the proposed structure of the endoperoxide by X-ray crystallography. Kinetics analysis of quantum yields provides rate constants for photophysical and photochemical events.

We report severe distortion to the structure of β‐cyclodextrin and partial de‐encapsulation of included guest prompted by strong π‐stacking of appended pyrene moieties in the self‐assembly of inclusion complex into toroidal nanostructures. The inclusion complex formed from bis(β‐cyclodextrin)‐substituted pyrene and bis(adamantane)‐substituted methyl viologen assembled into ring‐like structures. The rings undergo further self‐assembly which involve strong face‐to‐face π‐stacking of pyrene chromophores. Close approach of the pyrenes for π‐stacking demands severe distortion of the cyclodextrin truncated cone structure and partial de‐encapsulation of the guest from the cavity. The understanding that β‐CD can be distorted severely during self‐assembly may be helpful in the design of molecular architectures.

Hierarchical self-assemblies of β-cyclodextrin-linked pyrene and N-alkyl derivatives of pyromellitic diimides are studied in detail. The charge-transfer interaction between pyrene and pyromellitic diimide is augmented by β-cyclodextrin-pyromellitic diimide binding interactions in these cases. When the alkyl group is adamantyl, a 1:1 complex was formed with a very high association constant (K =1.82×10 m ). Here, the charge-transfer interaction is reinforced by inclusion binding of the adamantyl group in the β-cyclodextrin cavity leading to the formation of 2D sheets, which undergo twisting to give twisted fibres. When the alkyl group is tert-butyl, a 1:2 complex was formed with a high association constant (K =2.91×10 m ). A detailed analysis showed that the tert-butyl pyromellitic diimide undergoes both inclusion and rim-binding interactions with the β-cyclodextrin. The charge-transfer complex further self-assembled into chiral nanostructures as evident from SEM, TEM and AFM analysis. In the case of N-methyl-substituted pyromellitic diimide, the interaction with β-cyclodextrin-linked pyrene was only through rim binding, which resulted in the formation of a weak charge-transfer complex with K =4.2×10 m . Formation of a hierarchical assembly was not observed in this case. A rational mechanism for the self-assembly, which relies on the strength of the cyclodextrin-pyromellitic diimide complexation is presented.