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A new photocleavable analog of BAPTA chelating ligand has a high affinity towards Ca2+ ions (K = 2.5 × 106 M−1). The use of photolabile 3-(hydroxymethyl)-2-naphthol core in the design of photo-BAPTA allows for the efficient (Φ = 0. 63) and very fast (τ < 12 μs) release of Ca2+ ions upon 300 or 350 nm irradiation.

We report the occurrence of efficient energy transfer reaction in a novel host–guest assembly composed of an anionic clay nanosheet, cationic porphyrin, and neutral aromatic molecule encapsulated within a cationic organic cavitand. The supramolecular assembly was prepared by the coadsorption of tetracationic Zn–porphyrin (acceptor) and 2-acetylanthracene (donor) enclosed within cationic organic cavitand (octaamine in its protonated form) on anionic clay nanosheets. In this arrangement under the interguest distance of 2.4 nm, almost 100% efficiency of singlet–singlet energy transfer was achieved. Detailed time-resolved fluorescence measurements revealed that the energy transfer rate constant could be attributed to a single component (1.9 × 109 s–1). This strongly suggests that the adsorption distribution of porphyrin and cavitand is rather uniform, not segregated. This is a progress from our previous study that involves energy transfer between two encapsulated neutral molecules. The use of Zn–porphyrin as ...

Our long-range objective of developing surface anchored supramolecular assemblies as artificial light harvesting systems led us to explore the intercalation of guest molecules confined within octaamine hydrochloride (OAm·HCl) in the 2-dimensional galleries of layered inorganic material α-Zr(IV)phosphate (α-ZrP). Photophysical properties of 4,4'-dimethylbenzil, camphorthione, 4,4'-dimethylstilbene, pyrene and coumarin-1 were used to probe the intercalation behavior of OAm capsules within the galleries of α-ZrP. (1)H NMR and emission spectral investigations suggested the inclusion of guests within OAm and also confirmed the stability of host-guest complexes under acidic conditions in water. Stirring guest encapsulated OAm capsule with exfoliated α-ZrP nanosheets resulted in intercalation of the host-guest assembly as a whole in the case of 4,4'-dimethylbenzil, camphorthione, and 4,4'-dimethylstilbene as guests. According to powder X-ray diffraction and emission data these capsules are stable in the galleries of α-ZrP. The fact that the capsules are stable and can be included in α-ZrP nanosheets opens up further opportunities to explore inclusion of two different capsules, one with a donor and the other with an acceptor, and study the energy and electron transfer phenomenon between neutral molecules in α-ZrP galleries.

Optically pure α-alkyl deoxybenzoins resulting in products of Norrish Type I and Type II reactions upon excitation has been investigated within the octa acid (OA) capsule in water. The product distribution was different from that in an organic solvent and was also dependent on the length of the α-alkyl chain. Most importantly, a rearrangement product not formed in an organic solvent arising from the triplet radical pair generated by Norrish Type I reaction was formed, and its yield was dependent on the alkyl chain length. In an organic solvent, since the cage lifetime is shorter than the time required for intersystem crossing (ISC) of the triplet radical pair to the singlet radical pair the recombination with or without rearrangement of the primary radical pair (phenylacetyl and benzyl) does not occur. Recombination without rearrangement within the capsule as inferred from monitoring the racemization of the optically pure α-alkyl deoxybenzoins suggesting the capsule's stability for at least 10(-8) s (the time required for ISC) is consistent with our previous photophysical studies that showed partial opening and closing of the capsule in the time range of microseconds.

Nanocapsules, made up of the deep cavitand octa amine and several guests, were prepared in aqueous acidic solution and were found to be stable in the gas phase as detected by electrospray ionization mass spectrometry (ESI-MS). The observed gas phase host-guest complexes contained five positive charges and were associated with several acid molecules (HCI or HBr).

With the help of (1)H NMR and EPR techniques, we have probed the dynamics of guest molecules included within a water-soluble deep cavity cavitand known by the trivial name octa acid. All guest molecules investigated here form 2:1 (host/guest) complexes in water, and two host molecules encapsulate the guest molecule by forming a closed capsule. We have probed the dynamics of the guest molecule within this closed container through (1)H NMR and EPR techniques. The timescales offered by these two techniques are quite different, millisecond and nanosecond, respectively. For EPR studies, paramagnetic nitroxide guest molecules and for (1)H NMR studies, a wide variety of structurally diverse neutral organic guest molecules were employed. The guest molecules freely rotate along their x axis (long molecular axis and magnetic axis) on the NMR timescale; however, their rotation is slowed with respect to that in water on the EPR timescale. Rotation along the x axis is dependent on the length of the alkyl chain attached to the nitroxide probe. Overall rotation along the y or z axis was very much dependent on the structure of the guest molecule. The guests investigated could be classified into three groups: (a) those that do not rotate along the y or z axis both at room and elevated (55 degrees C) temperatures, (b) those that rotate freely at room temperature, and (c) those that do not rotate at room temperature but do so at higher temperatures. One should note that rotation here refers to the NMR timescale and it is quite possible that all molecules may rotate at much longer timescales than the one probed here. A slight variation in structure alters the rotational mobility of the guest molecules.

A supramolecular host-guest assembly composed of a cationic organic cavitand (host), neutral aromatic molecules (guests), and an anionic clay nanosheet has been prepared and demonstrated that in this arrangement efficient singlet-singlet energy transfer could take place. The novelty of this system is the use of a cationic organic cavitand that enabled neutral organic molecules to be placed on an anionic saponite nanosheet. Efficient singlet-singlet energy transfer between neutral pyrene and 2-acetylanthracene enclosed within a cationic organic cavitand (octa amine) arranged on a saponite nanosheet was demonstrated through steady-state and time-resolved emission studies. The high efficiency was realized from the suppression of aggregation, segregation, and self-fluorescence quenching. We believe that the studies presented here using a novel supramolecular assembly have expanded the types of molecules that could serve as candidates for efficient energy-transfer systems, such as in an artificial light-harvesting system.

In this report, we present methods of functionalization of AuNP's with deep-cavity cavitands that can include organic molecules. Two types of deep-cavity cavitand-functionalized AuNP's have been synthesized and characterized, one soluble in organic solvents and the other in water. Functionalized AuNP soluble in organic solvents forms a 1:1 host–guest complex where the guest is exposed to the exterior solvents. The one soluble in water forms a 2:1 host–guest complex where the guest is protected from solvent water. Phosphorescence from thiones and benzil included within heterocapsules attached to AuNP was quenched by gold atoms present closer to the guests included within deep-cavity cavitands. During this investigation, we have synthesized four new deep-cavity cavitands. Of these, two thiol-functionalized hosts allowed us to make stable AuNP's. However, AuNP's protected with two amine-functionalized cavitands tended to aggregate within a day.

Synthesis, inclusion properties, and ability to control excited-state properties of two water-soluble hosts are presented. These hosts surround the guest molecule(s) by forming a capsular assembly. By constraining the guest and by providing very little free space, the host is able to alter the excited-state behavior of guest molecules. The excited-state chemistry and physics of guest molecules are distinctly different from those in organic solvents.

The rotational mobility of organic guest molecules when included within a confined capsule is restricted and this feature could be translated into product selectivity as established with the photochemical behavior of cyclohexyl phenyl ketones.