We have been exploring the use of a deep cavity cavitand known by the trivial name 'octa acid' as a photochemical reaction cavity for manipulating photochemical and photophysical properties of organic molecules. In the current study, we have monitored the micropolarity of the interior of the cavitand by recording the fluorescence of five different organic probes. They all indicate that the interior of octa acid capsuleplex (2:1, H/G complex) is nonpolar and does not contain water molecules in spite of the complex being present in water. The nature of the octa acid-probe complex in each case has been characterized by 1H NMR data to be a 2:1 capsuleplex. Photophysical and 1H NMR experiments were employed to probe the factors that control the structure of the complex, 2:2, 2:1, and 1:1. The data we have on hand suggest that the structure of the host/guest complex depends on the size and hydrophobicity of the guest molecule.

The synthesis and properties of a new class of photoresponsive coumarin polyesters are described. Incorporation of the coumarin chromophore in the polymer chain provides interesting properties such as polymer chain crosslinking upon irradiation at 350 nm and chain un-cross-linking when irradiated at 254 nm. In addition, irradiation at 254 nm also results in polymer chain scission. The cross-linking, uncross-linking, and chain scission properties were studied by ssNMR, ATR-IR, and GPC measurements. These properties enable the fabrication of 2D surfaces having complementary micropatterned features. Also, initial biocompatibility profiles of the polymers and their irradiation products were demonstrated using MTT assays.

With the view to establishing the generality of cucurbit[8]uril as a template, the photodimerization of hydrochloride salts of eight azastilbenes has been investigated in an aqueous medium. Whereas in solution upon excitation all of these olefins yield products of geometric isomerization, cyclization, and hydration, in the presence of cucurbit[8]uril the predominant product is that of dimerization. Such a change in product distribution is attributed to the localization of the olefins by the host cucurbit[8]uril. Most importantly, instead of a mixture of dimers, predominantly a single dimer was obtained in each case. The nature of the dimer that was formed could be rationalized on the basis of the principles of "best fit" and "minimization of electrostatic repulsion". The superior ability of cucurbit[8]uril compared to micelles to act as a templating agent is attributed to its ability to provide a reaction cavity that is tight and time-independent.

Supramolecular complexation behavior of cucurbiturils with paramagnetic nitroxide spin probes was examined by (1)H NMR, X-ray diffraction studies of crystals, computation, and EPR. Both cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) form a 1:1 complex with 4-(N,N,N-trimethylammonium)-2,2,6,6-tetramethylpiperidinyl-N-oxy bromide (CAT1). The structure of the complex in the solid state was inferred by X-ray diffraction studies and in the gas phase by computation (B3LYP/6-31G(d)). Whereas ESI-MS data provided evidence for the existence of the complex in solution, indirect evidence was obtained through (1)H NMR studies with a structural diamagnetic analogue, 4-(N,N,N-trimethylammonium)-2,2,6,6-tetramethyl-N-methylpiperidine iodide (DCAT1). The EPR spectrum of the CAT1@CB7 complex consisting of three lines suggested that probe CAT1 is associated with host CB7 such that the nitroxide part is exposed to water. The spectral pattern was independent of the concentration of the complex and the presence of salt such as NaCl. The most interesting observation was made with CB8 as the host. In this case, in addition to the expected three-line spectrum, an additional spectrum consisting of seven lines was recorded. The contribution of the seven-line spectrum to the total spectrum was dependent on the concentration of the complex and added salt (NaCl) to the aqueous solution. The coupling constant for the seven-line spectrum for (14)N-substituted CAT1 is 5 G, and that for the four-line spectrum for (15)N-substituted CAT1 is 7.15 G. The only manner by which we could reproduce the observed spectra by simulation for both (14)N- and (15)N-substituted CAT1@CB8 was by assuming a spin exchange among three nitroxide radicals. To account for this observation, we hypothesize that three CAT1 molecules included within CB8 interact in such a way that there is an association of three supramolecules of CAT1@CB8 (i.e., [CAT1@CB8](3)) in a triangular geometry that leads to spin exchange between the three radical centers. We have established, with the help of 13 additional examples, that this is a general phenomenon. We are in the process of understanding this unusual phenomenon.

Thiocarbonyl compounds possess unusual photophysical properties: they fluoresce from S 2 , phosphoresce from T 1 only at extremely low concentrations in solution at room temperature, have unit quantum yield of intersystem crossing from S 1 to T 1 , undergo self-quenching at diffusion-controlled rates, and are quenched by ground-state oxygen leading to self-destruction. In this article, we are concerned with finding a new method to observe phosphorescence from thioketones at room temperature in aqueous solution at high concentrations. To achieve this goal, one needs to find ways to eliminate diffusion-limited self-quenching and oxygen quenching. We present here a general strategy that has allowed us to record phopshorescence from a number of thioketones in aqueous solution at room temperature. The method involves encapsulation of thioketone molecules within a "closed nanocontainer" made up of two cavitand molecules known by its trivial name as octa acid. In these supramolecular complexes, despite two thiocarbonyl compounds being present in close proximity, no self-quenching occurs within the confined space due to curtailment of their rotational freedom. Although phosphorescence could also be observed when these thioketones are included in open containers, such as cucurbiturils and cyclodextrines, the closed container made up of octa acid is found to be the best medium to observe phosphorescence from thioketones whose excited state chemistry is essentially controlled by self-quenching.