Supramolecular-Surface Photochemistry: Assembly and Photochemistry of Host–Guest Capsules on Silica Surface

Host cavitands and organic guest molecules independently adsorbed on silica particles when mixed and shaken in the presence of a few drops of water underwent intra- and interparticle migration to form capsular complexes that were not formed either in water or organic solvents. Importance of cavitand migration and tumbling on silica surface was established by demonstrating that covalently linked cavitands do not form capsular complexes. The encapsulated guests exhibited selective photochemistry as they do within an organic capsule in solution

Excited State Chemistry of Capsular Assemblies in Aqueous Solution and on Silica Surfaces

Synthesis and encapsulation properties of two new water-soluble resorcinol-capped organic cavitands (tetra acid and octa acid; RTA and ROA) are reported in this Letter. Organic guest molecules template the formation of capsular assembly of the above cavitands in water. Depending upon the guest, either 1:2 (guest to host) or 2:2 capsular assemblies were formed. The excited state properties of guests such as anthracene, camphorthione, and 4,4′-dimethyl benzil were distinctly different within a capsular assembly from those when they were free in a solution. Importantly, the host–guest complexes of the above two hosts (RTA and ROA) as well as octa acid (OA) could be transferred to a silica surface. The excited state behavior of host–guest assemblies on silica surface resembled that in solution. The high cage effect in the decarbonylation products and high yield of rearrangement product obtained upon photolysis of 1-phenyl-3-tolyl-2-propanone included within RTA, ROA, and OA both in solution and on silica surface supported the conclusion that capsular assemblies of these hosts are stable on silica surface

Supramolecular Surface Photochemistry: Cascade Energy Transfer between Encapsulated Dyes Aligned on a Clay Nanosheet Surface

Three coumarin derivatives (7-propoxy coumarin, coumarin-480, and coumarin-540a, <b>2</b>, <b>3</b>, and <b>4</b>, respectively) having different absorption and emission spectra were encapsulated within a water-soluble organic capsule formed by the two positively charged ammonium-functionalized cavitand octaamine (OAm, <b>1</b>). Guests <b>2</b>, <b>3</b>, and <b>4</b> absorb in ultraviolet, violet, and blue regions and emit in violet, blue, and green regions, respectively. Energy transfer between the above three coumarin@(OAm)₂ complexes assembled on the surface of a saponite clay nanosheet was investigated by steady-state and time-resolved emission techniques. Judging from their emission and excitation spectra, we concluded that the singlet–singlet energy transfer proceeded from <b>2</b> to <b>3</b>, from <b>2</b> to <b>4</b>, and from <b>3</b> to <b>4</b> when OAm-encapsulated <b>2</b>, <b>3</b>, and <b>4</b> were aligned on a clay surface as two-component systems. Under such conditions, the energy transfer efficiencies for the paths <b>2</b>* to <b>3</b>, <b>2</b>* to <b>4</b>, and <b>3</b>* to <b>4</b> were calculated to be 33, 36, and 50% in two-component systems. When all three coumarins were assembled on the surface and <b>2</b> was excited, the energy transfer efficiencies for the paths <b>2</b>* to <b>3</b>, <b>2</b>* to <b>4</b>, and <b>3</b>* to <b>4</b> were estimated to be 32, 34, and 33%. A comparison of energy transfer efficiencies of the two-component and three-component systems revealed that excitation of <b>2</b> leads to emission from <b>4</b>. Successful merging of supramolecular chemistry and surface chemistry by demonstrating novel multi-step energy transfer in a three-component dye encapsulated system on a clay surface opens up newer opportunities for exploring such systems in an artificial light-harvesting phenomenon

Anticancer Agent with Inexplicable Potency in Extreme Hypoxia: Characterizing a Light-Triggered Ruthenium Ubertoxin

Tumor hypoxia renders treatments ineffective that are directly (e.g., radiotherapy and photodynamic therapy) or indirectly (e.g., chemotherapy) dependent on tumor oxygenation. This study introduces a ruthenium compound as a light-responsive anticancer agent that is water-soluble, has minimal dark cytotoxicity, is active at concentrations as low as 170 pM in ∼18.5% O2 normoxia and near 10 nM in 1% O2 hypoxia, and exhibits phototherapeutic indices as large as >500,000 in normoxia and >5,800 in 1% O2 hypoxia using broadband visible and monochromatic blue light treatments. These are the largest values reported to date for any compound class. We highlight the response in four different cell lines to improve rigor and reproducibility in the identification of promising clinical candidates