Photochemistry and Photophysics of Cholesta-5,7,9(11)-trien-3β-ol in Ethanol.

Cholesta-5,7,9(11)-trien-3β-ol (9,11-dehydroprovitamin D, CTL) is used as a fluorescent probe to track the presence and migration of cholesterol in vivo. We recently described the photochemistry and photophysics of CTL in degassed and air-saturated tetrahydrofuran (THF) solution, an aprotic solvent. The zwitterionic nature of the singlet excited state, CTL* is revealed in ethanol, a protic solvent.

α-Methylstilbene Isomers: Relationship of Structure to Photophysics and Photochemistry.

Significant differences in the photochemical and photophysical behavior of -α-methylstilbene and -stilbene have been attributed to structural changes caused by the steric requirements of the methyl group. We present here the X-ray structures of - and -α-methylstilbene (- and -MeSt). This is the first X-ray structure of a -stilbene.

Photochemistry and photophysics of cholesta-5,7,9(11)-trien-3β-ol: a fluorescent analogue of cholesterol.

Cholesta-5,7,9(11)-trien-3β-ol (9,11-dehydroprovitamin D, 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.

Generation of Long-Lived Photoinduced Charge Separation in a Supramolecular Toroidal Assembly.

Efficiencies of artificial photosynthetic and photocatalytic systems depend on their ability to generate long-lived charge-separated (CS) states in photoinduced electron transfer (PET) reactions. PET, in most cases, is followed by an ultrafast back electron transfer, which severely reduces lifetime and quantum yield of CS states. Generation of a long-lived CS state is an important goal in the study of PET reactions.

Translational Diffusion and Unstable Conformer Trapping in Glassy Isopentane at 77 K.

Diffusional quenching in isopentane (IP) glass at 77 K is demonstrated by the reduction of triphenylene phosphorescence lifetimes in the presence of 1,3-pentadiene and/or molecular oxygen. Fluorescence spectra and lifetimes of - and -1,2-di(1-methyl-2-naphthyl)ethene in IP glass at 77 K reveal that the → photoisomerization leads to the trapping of unstable conformers of the isomer. The claim that IP at 77 K is not sufficiently viscous to trap unstable photoproduct conformers is invalidated.

Effect of N-Alkyl Substituents on the Hierarchical Self-Assembly of β-Cyclodextrin-Linked Pyrene-Pyromellitic Diimide Charge-Transfer Complexes.

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.

Observation of Supramolecular Chirality in a Hierarchically Self-Assembled Mixed-Stack Charge-Transfer Complex.

Supramolecular chirality was observed in a charge-transfer (CT) complex formed by self-assembly of β-cyclodextrin-linked pyrene and adamantane-linked pyromellitic diimide in water. In the complex, the pyrene-pyromellitic diimide CT interaction is reinforced several-fold by the strong β-cyclodextrin-adamantane inclusion binding interaction, as confirmed by H NMR, absorption, fluorescence and isothermal titration calorimetry studies. The CT complex exhibited high stability, as inferred from the temperature-dependent absorption and NMR studies.