Role of Free Space and Conformational Control on Photoproduct Selectivity of Optically Pure α‑Alkyldeoxybenzoins within a Water-Soluble Organic Capsule

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

Supramolecular-Surface Photochemistry: Supramolecular Assembly Organized on a Clay Surface Facilitates Energy Transfer between an Encapsulated Donor and a Free Acceptor

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 an energy acceptor in this study enables to connect this energy transfer system to charge separation processes in the same manner as natural photosynthetic systems do; moreover, the efficiency of energy transfer reaction improved to almost 100% from 85% in the previous system between two cavitands

Gold Nanoparticles Functionalized with Deep-Cavity Cavitands: Synthesis, Characterization, and Photophysical Studies

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

Capsular Complexes of Nonpolar Guests with Octa Amine Host Detected in the Gas Phase

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 (HCl or HBr)