The observed redshift is also consistent with the decrease in the HOMO-LUMO energy gap as the cluster size increases (see section 3.2), indicating that smaller energy is required for electronic transitions. Furthermore, the changes observed in the UV-Vis spectra are consistent with the surface plasmon resonance (SPR) efect, which is characteristic of metal nanoparticles. The SPR efect results from the collective oscillation of electrons in response to light, which is stronger for larger clusters due to increased electron delocalization and interactions between Pt3 units. This efect contributes to the significant redshift and broadening of the absorption bands as the cluster size increases.