Effect of surface modification of hydrophilic organic molecules on the energy gap of Si nanoparticles

The effects of surface modification with hydrophilic molecules on the electronic structure of silicon nanoclusters were investigated by using Density Functional Theory (DFT), with the aim of tuning the HOMO-LUMO gap for potential bio-labeling applications. We performed DFT calculations performed on Si10, Si39, and Si62 clusters terminated with representative acids like propionic and maleic acid. Results revealed that while most acids caused only minor HOMO-LUMO gap reductions, maleic acid termination led to a markedly greater reduction. This is attributed to a significant lowering of the LUMO energy level via interaction with its conjugated π-system. This effect was consistently observed and largely independent of the Si cluster size or number of attached maleic acid molecules. These findings suggest this is a highly promising strategy for enabling the long-wavelength emission required for advanced applications.