The golden rule to address charge transfer in dibenzenthiols-derivates/gold nanoparticles hybrids

Organic molecule–gold nanoparticles (Au NPs) hybrids based on a luminescent small organic molecule 4,4′-((((5,6-bis((2-hexyldecyl)oxy)benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(thiophene-5,2-diyl))bis(methanylylidene))bis(azanylylidene))dibenzenethiol (BTTh) and plasmonic Au NPs, with size ranging from 30 to 120 nm, were engineered and compared with layers of BTTh on gold film and glass and characterized by spectroscopic ellipsometry, Raman spectroscopy, Photoluminescence (PL) current–voltage (CV) measurements, atomic and Kelvin probe force microscopy. We found that their optical, structural and morphological properties changed with size. Specifically, we found that Au NPs with size ≤70 nm allow formation of uniform BTTh monolayers with short and strong Au–S bond promoting charge transfer processes from Au to BTTh. Through the construction of the energy levels scheme of BTTh–Au NPs hybrids, we discussed the effects of NPs size on the relative energy position between the HOMO–LUMO levels of BTTh and the work function (WF) and localized surface plasmon resonance (LSPR) of Au NPs, rationalizing the charge transfer process occurring between Au NPs and BTTh. These findings provided a versatile tool to design appropriate combinations of organic molecules–metal nanoparticles aimed to hybrid materials for optoelectronic applications.