Designing supramolecular architectures with uncommon geometries embedded with functional building units is of immense importance in contemporary research. In this report, we present a new water-soluble Pd 12 L 6 supramolecular coordination nanocage (1) that was synthesized via selfassembly of a tetradentate donor (L) with ditopic acceptor cis-[(en)Pd-(NO 3 ) 2 ] [en = ethylenediamine]. Self-assembly of a tetratopic donor with a cis-blocked 90°acceptor commonly produces tri/tetra-or hexagonal barreltype structures. However, the resulting cage 1 has an uncommon geometry consisting of two triangular cupolas conjoined through an irregular common hexagonal base. Incorporation of the benzothiadiazole unit in the structure helped in the photogeneration of reactive oxygen species (ROS) in water. Many nanomaterials have shown to have the ability to mimic the catalytic activity of natural enzymes (nanozymes). Majority of such nanozymes are water insoluble metal/metal-oxide nanoparticles or extended metal organic frameworks (MOFs)/metal−carbon composites, etc. The present water-soluble Pd 12 nanocage 1 has shown excellent oxidase-like activity upon irradiation with white light. The enzymatic activity of 1 is photoregulated which offers other obvious advantages, such as external control of enzymatic activity and noninvasiveness. The oxidase-like activity and exogenous ROS generation have been further exploited in photocatalytic antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) bacterial strain.

Light-harvesting is one of the key steps in photosynthesis, but developing artificial light-harvesting systems (LHSs) with high energy transfer efficiencies has been a challenging task. Here we report fluorescent hexagonal Pt­(II) metalla­cycles as a new platform to fabricate artificial LHSs. The metalla­cycles (4 and 5) are easily accessible by coordination-driven self-assembly of a triphenyl­amine-based ditopic ligand 1 with di-platinum acceptors 2 and 3, respectively. They possess good fluorescence properties both in solution and in the solid state. Notably, the metalla­cycles show aggregation-induced emission enhancement (AIEE) characteristics in a DMSO–H2O solvent system. In the presence of the fluorescent dye Eosin Y (ESY), the emission intensities of the metalla­cycles decrease but the emission intensity of ESY increases. The absorption spectrum of ESY and the emission spectra of the metalla­cycles show a considerable overlap, suggesting the possibility of energy transfer from the metalla­cycles to ESY, with an energy transfer efficiency as high as 65% in the 4 a +ESY system.

Donor−acceptor Stenhouse adducts (DASA) are new-generation photochromic compounds discovered recently. DASA exist normally in open form (blue/violet) and readily convert to cyclic (light yellow/colorless) zwitterionic form reversibly in the presence of green light in toluene/dioxane. In aqueous medium, the open form is not stable and converts to the cyclic zwitterionic form irreversibly. We report here a new selfassembled Pd 8 molecular vessel (MV) that can stabilize and store the open form of DASA even in aqueous medium. Reaction of the 90°acceptor cis-(tmeda)Pd(NO 3 ) 2 (M) [tmeda = N,N,N′,N′tetramethylethane-1,2-diamine] with a symmetric tetraimidazole donor (L, 3,3′,5,5′-tetra(1H-imidazol-1-yl)-1,1′-biphenyl) in a 2:1 molar ratio yielded a water-soluble [8+4] self-assembled M 8 L 4 molecular barrel (MV). This barrel (MV) is found to be a potential molecular vessel to store and stabilize the open forms of DASA in aqueous medium over the more stable zwitterionic cyclic form, while in the absence of the barrel the same DASA exist in cyclic zwitterionic form in aqueous medium. The hydrophobic interaction between the cavity and the open form of DASA molecules benefits reaching an out-of-equilibrium or reverse equilibrium state in aqueous medium. The presence of excess MV could even drive the conversion of the stable cyclic form to the open form in aqueous medium. The host−guest complex is stable upon irradiating with green light. To the best of our knowledge, this is the first successful attempt to stabilize the open form of DASA molecules in aqueous medium and the first report on the fate of DASA in a confined space discrete molecular architecture. Furthermore, the molecular vessel has been utilized for catalytic Michael addition reactions of a series of nitrostyrene derivatives with 1,3-indandione in aqueous medium.

Control over the stimuli-responsive behavior of smart molecular systems can influence their capability to execute complex functionalities. Herein, we report the development of a suite of spiropyran-based multi-stimuli-responsive self-assembled platinum(II) macrocycles (5−7), rendering coordination-assisted enhanced photochromism relative to the corresponding ligands. 5 showed shrinking and swelling during photoreversal, while 6 and 7 are fast and fatigue-free supramolecular photoswitches. 6 turns out to be a better fatigue-resistant photoswitch and can retain an intact photoswitching ability of up to 20 reversible cycles. The switching behavior of the macrocycles can also be precisely controlled by tuning the pH of the medium. Our present strategy for the construction of rapid stimuli-responsive supramolecular architectures via coordination-driven self-assembly represents an efficient route for the development of smart molecular switches.

Fullerene extracts obtained from fullerene soot lack their real application due to their poor solubility in common solvents and difficulty in purification. Encapsulation of these extracts in asuitable host is an important approach to address these issues.W ep resent an ew Pd 6 barrel (1), whichi s composed of three 1,4-dihydropyrrolo[3,2-b]pyrrole panels, clipped through six cis-Pd II acceptors.L arge open windows and cavity make it an efficient host for alarge guest. Favorable interactions between the ligand and fullerene (C 60 and C 70 ) allows the barrel to encapsulate fullerene efficiently.Thorough investigation reveals that barrel 1 has as tronger binding affinity towards C 70 over C 60 ,r esulting in the predominant extraction of C 70 from am ixture of the two.F inally,t he fullerene encapsulated barrels C 60 &1 and C 70 &1 were found to be efficient for visible-light-induced singlet oxygen generation. Such preferential binding of C 70 and photosensitizing ability of C 60 &1 and C 70 &1 are noteworthy.

Development of photosensitizer-based self-assembled metallosupramolecular architectures with important applications is an emerging trend in supramolecular chemistry. In this study, we report a new benzothiadiazole-based tetra-pyridyl ligand (L), which upon self-assembly with a cis-block 90° Pt­(II) acceptor generated an unprecedented tetrafacial Pt­(II)8 photoactive tubular molecular cage (PMB1). This cage could bring an extraordinary photosensitizer, benzothiadiazole, into water which is otherwise insoluble. PMB1 is fluorescent and shows photogeneration of singlet oxygen in an aqueous medium. These features make PMB1 a potent antimicrobial agent in water in both the presence and absence of light. In comparison to its building blocks and water-soluble alkylated charged ligand ([L Me4 ]­[4NO 3 ]), the cage shows much enhanced photoinduced antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) as a representative of Gram-positive bacteria and Pseudomonas aeruginosa (PA) as a representative of Gram-negative bacteria. PMB1 is successful at inactivating the bacterial growth via both photoactivation of molecular oxygen and membrane depolarization mechanisms, thus proving to be a dual warhead. Inactivation of bacteria in water using such a supramolecular architecture is noteworthy and can shed light on the generation of new antimicrobial supramolecular systems.

A new triphenylamine-based tetraimidazolium salt L was developed for silver(I)−carbene bond-directed synthesis of tetranuclear silver(I) octacarbene ([Ag 4 (L) 2 ](PF 6 ) 4 ) metallacage 1. Interestingly, after assembly formation, metallacage 1 showed a nine-fold emission enhancement in dilute solution while ligand L was weakly fluorescent. This is attributed to the rigidity induced to the system by metal− carbene bond formation where the metal center acts as a rigidification unit. The enhanced emission intensity in dilute solution and the presence of the triphenylamine core made 1 a potential candidate for recognition of picric acid (PA). This recognition can be ascribed to the dual effect of ground-state charge-transfer complex formation and resonance energy transfer between the picrate and metallacage 1. For metallacage 1, a considerable detection limit toward PA was observed. The use of such metal−carbene bond-directed rigidification-induced enhanced emission for PA sensing is noteworthy.

Developing artificial light-harvesting scaffolds with a cascade energy transfer process is significant for better understanding of photosynthesis. Here, we report [3+3] self-assembled Pt II fluorescent macrocycles (3 a and 3 b) as light-harvesting platforms with cascade energy transfer. The Pt II macrocycles aggregate into nanospheres and show emission-enhancement characteristics upon increasing water content in acetone medium. These aggregates (3a a and 3b a ) serve as energy donors when mixed with the hydrophobic dye Eosin-Y (ESY). In the presence of a second dye, Nile Red (NiR), an unusual sequential two-step energy transfer takes place from the macrocycles to NiR. In this case, ESY acts as a bridge in the relay mode. Additionally, a unique strategy to control such an energy transfer process by tuning the chain length of the alkyl group attached to the periphery of the macrocycles is demonstrated.