Following a comprehensive investigation of the photothermal mechanism governing the assembly process, our next objective was to test how the addition of an external PTA would affect the dynamics of the system. To achieve this goal, we opted for palladium nanoparticles as their absorption spectrum closely resembles that of Co-DHBDC and which could form interesting materials in the case composite formation. Thus, we synthesized cubic palladium nanoparticles (PdNP) measuring between ≈10-12 nm that exhibited absorption across the visible region with an increase towards shorter wavelengths (Fig. and). Initially a 0.5 OD (OD at 520 nm) concentration of PdNPs was introduced to the standard photothermal synthesis of Co-DHBDC previously described and irradiated at 520 nm. This resulted in MOF assembly akin to previous observations, with the nanoparticles found to be incorporated to the MOF assemblies in a composite manner (Fig. , and Supplementary Figs. ). When utilizing 660 nm light to initiate the same reaction, thick rod-like structures were obtained with palladium predominantly on the surface of the MOF particles (Fig. , and Supplementary Figs. ). Further examination of the temperature profile revealed that at a concentration of 0.5 OD PdNPs, the system underwent approximately 14 heating cycles (each lasting an average of 189±9 s) under 520 nm light irradiation during a 1 h reaction period (Fig. , and Supplementary Fig. ). Increasing the palladium concentration to 1 OD (OD at 520 nm) resulted in 32 heating cycles under 520 nm light (each lasting approximately 61±3 s) bringing its photothermal capacity to be comparable with the Co-DHBDC in the solution (Fig. , and Supplementary Fig. ). Interestingly, in presence of 1 OD of palladium NPs under 520 nm LED, no assemblies of Co-DHBDC were observed, as confirmed by SEM (Fig. , and Supplementary Fig. ). These observations demonstrate that under photothermal conditions at 520 nm, the presence of high concentrations of palladium nanoparticles suppresses the assembly of Co-DHBDC. A photo-switching experiment also attempted in presence of 0.5 OD Pd with sequential activation using 660 nm and then 520 nm light. However, in this case, a complete uniform assembly of the palladium-Co-DHBDC larger rods formed using 660 nm light, were not isolated after irradiation with 520 nm light (Supplementary Fig. ). This observation also points to the requisite of optimum size, and surface functionality of the initial MOF structure generated in situ for the assembly process. These experiments not only reinforce the proposed photothermal activation mechanism and the concept of dominant photothermal heating but also lead to the synthesis of nanoparticle-MOF composites. These composites have potential applications in diverse disciplines , and the developed concept could be further leveraged to create a variety of morphologies, impacting the intended applications.