In previous reports, Co-DHBDC synthesized utilizing a conventional heating method is shown to be formed via the coordination of Co 2+ with the carboxyl and hydroxyl groups of DHBDC creating CoO6 octahedra connected by organic linkers (Supplementary Fig. ). In addition, Co-DHBDC is known to possess the highest density of metal sites reported to date in MOFs, and high stability due to the fully coordinated oxygen in the carboxyl and hydroxyl of the DHBDC. The rod Co-DHBDC structures obtained through conventional heating are approximately 1200 nm in length, and 140 nm in width (Fig. ). Instead, photothermal heating yielded assembly of individual nanorods into the superstructure with a length of ≈5000 nm, and width of ≈3800 nm (Fig. ). This consists of nearly 1000-1500 numbers of nanorods in a closed-pack assembly with few individual nanorods protruding outside in a hedgehog fashion as clearly observed from TEM tomography (Supplementary Fig. , and Supplementary Movie 1). Elemental analysis confirms the presence of cobalt and oxygen as the main constituents of the Co-DHBDC structures both under photothermal and conventional heating conditions (Fig. and). SEM images of the obtained assembly of nano MOFs exhibit a uniform morphological feature, and notably, the assemblies were obtained as a reasonably stable dispersion in polar solvents, and are morphologically robust for centrifugation or ultrasonication, thus suitable for practical applications (Fig. , Supplementary Fig. and). The UV-Vis absorption spectra shows that the metal precursor and Co-DHBDC both absorb throughout the visible region (≈450-730 nm), but at ≈520 nm, Co-DHBDC has higher absorption while the molecular precursor's absorption is significantly lower (Fig. ). XRD analysis further reveals the characteristic peaks of the crystalline MOF structures obtained through both of the heating methods as mentioned above (Fig. , and Supplementary Fig. ). Moreover, XPS indicated no significant change in cobalt oxidation state in the MOF structures obtained as compared to conventional heating method (Fig. ). The photothermal synthesis and assembly of Co-DHBDC thus indicate a differential heating method employed during the reaction, as compared to conventional heating, leading to a substantially different synthetic outcome. Therefore, a detailed mechanistic investigation is carried out to comprehend the photothermal synthesis, and assembly process.