Self-assembly of a cis-blocked Pd(II) 90° ditopic acceptor [ cis-(tmeda)Pd(NO)] (M) with a tetradentate donor L [benzene-1,4-di(4-terpyridine)] in 2:1 molar ratio yielded two isometric molecular barrels MB1 and MB3 in DMSO [tmeda = N, N, N' N'-tetramethylethane-1,2-diamine]. Exclusive formation of the symmetrical tetrafacial barrel (MB1) was achieved when the self-assembly was performed in aqueous medium. The presence of a large confined cavity makes MB1 a potential molecular container. Spiropyran (SP) compounds exist in stable closed spiro form in visible light and convert to transient open merocyanine (MC) form upon irradiation with UV-light or upon strong heating. The transient MC form readily converts to the stable closed SP form in visible light. MB1 has been employed as a safe container to store the planar and unstable merocyanine isomers (MC1/2) of different spiropyran molecules (SP1/2) [SP1/2 = 6-bromo-spiropyran and 6-nitrospiropyran] for several days. The transient MC forms (MC1 and MC2) were found to be stable inside the molecular container MB1 under visible light and even in the presence of different stimuli such as heat and UV light for a long time. Such stabilization of MC forms inside the confined cavity of MB1 is noteworthy. This phenomenon was generalized by utilizing a carbazole-based molecular barrel (MB2) as a host, which also showed a similar stabilization of transient MC form in visible light at room temperature. Moreover, reverse thermochromism was observed as a result of heating of the MC1 ⊂ MB2 complex, which de-encapsulates the guest in the form of SP1 to give a colorless solution. Moreover, both the host molecules (MB1, MB2) were capable of stabilizing transient MC2 even in the solid state. Such stabilization of transient MC forms in the solid state and transformation of SP forms to MC forms in the solid state in the presence of molecular barrel are remarkable, and these properties have been employed in developing a magic ink.

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.

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.

Four new metal–carbene based metallacycles and metallocages have been obtained using non-AIE active 1,4-dihydropyrrolo[3,2-b]pyrrole based imidazolium ligands. These final assemblies show linkage induced enhanced emission via rigidification.

A tetraphenylethylene (TPE)-based flexible imidazolium (L) salt was used to develop a di-nuclear silver(I)−tetracarbene (1) complex. Coordination-induced rigidity upon formation of 1 exhibited a 6-fold increase in emission intensity in acetonitrile compared to starting L. Despite TPE being a well-known aggregation-induced emissive moiety, Ag I −N-heterocyclic carbene (NHC) complex 1 had a remarkably higher fluorescence emission (4-fold) in dilute solution when compared with L in its aggregated state. Finally, this enhanced emission was used to institute a new platform for an artificial light-harvesting system. 1 acted as an energy donor and efficiently transferred energy to Eosin Y (ESY) with a high saturation at a 67:1 (1/ESY) molar ratio. Use of rigidification-induced emission of the Ag I −NHC complex to fabricate a light-harvesting scaffold is a new approach and can greatly impact the generation of smart materials.

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.

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