Metal−ligand coordination driven self-assembly has evolved as a very powerful approach to construct discrete nanometer-sized molecular architectures which uses molecular building blocks with rigid geometries. many aesthetically elegant ‘container molecules’ possessing cavities of well-defined shape, size and functionality have been synthesised by this approach which found potential applications in guest encapsulation, separation, catalysis, drug delivery, stabilisation of reactive species etc. the hydrophobic nature of their cavities can potentially mimic the substrate binding site buried under protein molecules in enzymes. interestingly, a very large number of such three dimensional host molecules have closed-shell topology hence; they possess comparatively smaller windows with respect to their cavities, which in turn restrict bigger guest molecules to go inside. cylindrical or barrel shaped architectures are exceptions as they possess apertures similar to their cavity size. even in biology, barrel-shaped proteins, viz. β-barrels have immense importance in the diffusion of small molecules and ions through cell membranes. however, the synthesis of discrete molecular barrels by metal-ligand self-assembly remains very challenging and scarcely reported in the literature. to construct a molecular barrel, we introduced a novel less-symmetric tetraimidazole donor l (1,3,6,8-tetra(1h-imidazol-1-yl)-9-methyl-9h-carbazole) based on carbazole backbone; although the imidazole based donors are difficult to handle due to the rotational flexibility of the imidazole moiety. moreover, the non-symmetric nature of the donor enormously increases the complexity of the self-assembly process. l was synthesised from its tetrabromo analogue- 1,3,6,8-tetrabromo-9-methyl-9h-carbazole via a cui catalysed c-n coupling reaction with imidazole and was completely characterised by nmr spectroscopy, esi-ms spectrometry and single crystal x-ray diffraction analysis (scxrd). the imidazoles moieties closer to the n-methyl group are found severely twisted out of the carbazole plane compared to the rest due to steric repulsion. the self-assembly was performed by overnight heating a clear solution of l and cis-[(tmeda)pd(no3)2] (tmeda = n,n,n′,n′-tetramethylethane-1,2-diamine) in dmso in 1:2 stoichiometry. the product (psmbr-1), which is highly soluble in water was isolated as off-white solid in quantitative yield by treating the final solution with excess etoac. nmr spectroscopy (1h, 1h-1h cosy, dosy) suggested the formation of a single product. the composition of the assembly was precisely determined by high resolution esi-ms spectrometry which confirmed the formation of a pd8l4 species. finally, the structure of psmbr-1 was unambiguously established by the scxrd analysis of its coronene encapsulated complex, showing its tetrafacial open barrel topology where four panel-like ligand units are connected together in head-to-head fashion by eight pd(ii) acceptors. the dimension of the cavity is found to be 11.7 × 11.4 × 10.5 Å3 which is occupied by two coronene molecules. interestingly, the crystal structure also showed that the opposite ligand panels of the centrosymmetric molecular barrel are identical and related to each other by a center of symmetry, however, different from the adjacent ones. the distances between the two sets of opposite walls of the cavity differ by ∼2.7 Å. the newly engineered molecular barrel was found to be excellent host for water insoluble polyaromatic hydrocarbons (pahs). the encapsulations were carried out by stirring excess guest molecules with clear aqueous solution of psmbr-1 and the encapsulated complexes were characterised by various spectroscopic techniques including nmr, uv-vis and fluorescence spectroscopy. finally, when hela cells were incubated with the aqueous solution of perylene encapsulated psmbr-1 complex for 30 min and fluorescent microscopy images were recorded for the treated cells, brilliant blue emission from the cytoplasm part was observed, while the cells appeared to be healthy without any morphological change. very less toxicity observed from the facs analysis at experimental concentration of the fluorophore complex clearly suggested that psmbr-1 can be used safely as a potential vehicle to carry insoluble payloads inside live cells.